The main malfunctions of armature windings are electrical breakdown of insulation on the body or bandage, short circuit between turns and sections, mechanical damage ration. When preparing the armature for repair by replacing the winding, clean it from oil dirt, remove the old bands and, having soldered the collector, remove the old winding, having previously recorded all the data necessary for the repair.
In micanite-insulated armatures it is often very difficult to remove the winding sections from the slots. If the sections cannot be removed, heat the armature in an oven to 120–150 degrees, maintaining the temperature for 40–45 minutes, and then remove them.
For electric cars DC, coming in for repair, most often the coils of additional poles wound with a rectangular copper busbar are damaged or on an edge. It is not the coil's copper bus itself that is damaged, but the insulation between its turns. Repairing a coil comes down to restoring the interturn insulation by rewinding the coil.
Armature windings made of round wire are usually replaced during repairs. The armature windings of low-power machines are wound manually directly into the grooves of the core. The grooves, the ends of the core and the section of the shaft adjacent to the core are pre-insulated; grooves are milled in the collector.
According to the markings, install the wire into the slot of the collector plate (the beginning of the section) and manually insert it into the corresponding grooves, making the required number of turns. The end of the section is inserted into the slot of the corresponding collector plate.
The coil windings of the armatures of medium power electric machines are wound on templates. Each coil is wound separately. If the coil consists of several sections, then all sections are wound at once.
In industrial enterprises, the repair of armature windings from a rectangular drive, as a rule, includes the repair of individual or replacement of one or more failed coils.
When repairing pole windings, they are usually removed from the poles. To do this, unscrew the bolts securing the poles to the housing, remove the poles from the housing and remove them from the winding. When repairing the windings of additional poles, they find the location of the damage and, if it is a breakdown in the housing, clean it of damaged insulation and apply new one. If the intact insulation has served for quite a long time, then it needs to be replaced. When there is a turn short circuit, the body insulation is removed from the coil, the turns are moved apart and new turn insulation is laid between them. As a rule, the insulation is coated with adhesive varnishes and dried. The insulated winding is coated with enamel several times and dried.
Topic 3.3. Repair of ballasts
Types and causes of damage to ballasts. Repair of contacts and mechanical parts of contactors, starters, circuit breakers. Repair of coils.
Starter control equipment has the following types of damage: excessive heating of starter coils, contactors and automatic machines, interturn short circuits and short circuits to the coil body; excessive heating and wear of contacts; poor insulation; mechanical problems. The reason for dangerous overheating of AC coils is the jamming of the electromagnet armature in its open position and the low supply voltage to the coils. Interturn short circuits can occur due to climatic influences on the coil, as well as due to poor winding of the coils. A short circuit to the housing occurs when the frameless coil does not fit tightly on the iron core, as well as due to vibrations. The heating of contacts is affected by current load, pressure, size and contact opening, cooling conditions and oxidation of their surface and mechanical defects in the contact system. Contact wear depends on the current, voltage and duration of the electric arc between the contacts, the frequency and duration of switching on, the quality and hardness of the material. Mechanical problems in devices arise as a result of the formation of rust, mechanical breakdowns of axles, springs, bearings and other structural elements.
Before repairs, all major parts of the contactor are inspected to determine which parts need to be replaced and rebuilt. If the contact surface is slightly burned, it is cleaned of soot and deposits with an ordinary personal file and glass paper. When replacing contacts, they are made from copper cylindrical or shaped rods made of solid copper, grade M-1.
When repairing contactors, adhere to the rated contact pressure values. Deviation from them in one direction or another can lead to unstable operation of the contactor, causing it to overheat and weld the contacts.
A special feature of the repair of magnetic starters is the replacement of faulty coils and thermal elements. When making a new coil, it is necessary to maintain its design. Thermal elements of starters, as a rule, are replaced with new factory ones, because It is difficult to repair them in a workshop.
In A-series circuit breakers and other structurally similar switches, damage is mainly caused to the contacts that disconnect the mechanism and mechanical springs. Depending on the nature of the damage, circuit breakers are repaired in an electrical repair shop or at the place of their installation. Sooty copper-coated steel plates of the grate are carefully cleaned with a wooden stick or a soft steel brush, freeing them from a layer of carbon deposits, and then wiped with clean rags and washed.
The manufacturing process of coils consists of the operations of winding, insulating, impregnation, drying and monitoring. The coils can be wound on a winding template, on a frame or directly on an insulated pole.
Page 12 of 14
Basic information about windings.
In this section, information about windings and methods for their repair is given only to the extent that an electrician should know about them in order to competently carry out electrical plumbing operations for repairing electrical machines.
The winding of an electric machine is formed from turns, coils and coil groups.
A turn is the name given to two conductors connected in series, located under adjacent opposite poles. The required (total) number of turns of the winding is determined by the rated voltage of the machine, and the cross-sectional area of the conductors is determined by the current of the machine; the cue ball can consist of several parallel conductors.
A coil is several turns, laid with corresponding sides in two grooves and connected to each other in series. The parts of the coil lying in the grooves of the core are called slotted or active, and those located outside the grooves are called frontal.
The coil pitch is the number of slot divisions enclosed between the centers of the slots into which the sides of the turn or coil fit. The coil pitch can be diametrical or shortened. The diametrical pitch is the coil pitch equal to the pole division, and the shortened pitch is somewhat less than the diametrical pitch.
A coil group consists of several series-connected coils of the same phase, the sides of which lie under two adjacent poles.
The winding is several coil groups placed in grooves and connected according to a certain pattern.
An indicator characterizing the winding of an alternating current electric machine is the number of slots q per pole and phase, indicating how many coil sides of each phase there are. per one pole of the winding. Because, reel-to-reel
the sides of one phase lying under two adjacent poles of the winding form a coil group, then the number q shows the number of coils that make up the coil groups of a given winding.
The windings of electrical machines are divided into loop, wave and combined. According to the method of filling the slots, the windings of electrical machines can be single-layer or double-layer. With a single-layer winding, the side of the coil occupies the entire slot along its height, and with a double-layer winding, only half of the slot; its other half is filled by the corresponding side of the other coil.
The methods of laying the windings in the grooves depend on the shape of the latter. The grooves of stators, rotors and armatures of electrical machines can be of the following types: closed - into which the coil wires are inserted from the end of the core; semi-closed - into which the coil wires are inserted (“poured in”) one at a time through a narrow slot of the groove; semi-open - into which rigid coils are inserted, divided into two in each layer; open - into which rigid coils are placed.
In machines of older designs, the windings are held in grooves by wedges made of wood, and in modern machines by wedges made of various solid insulating materials or bandages. Various slot shapes of electrical machines have been shown in Fig. 98.
The windings of electrical machines are made in accordance with the drawing, in which their circuits are shown conventionally and represent a graphical representation of the scan of the circumference of the stator, rotor or armature. Such schemes are called expanded. These diagrams can be used to depict the windings of electrical machines of all types, both direct and alternating current, however, in repair practice, to depict the diagrams of double-layer windings of stators of alternating current electric machines, in recent years, predominantly end diagrams have been used, which are characterized by ease of execution and greater clarity. The end diagram of a two-layer stator winding of a four-pole machine is shown in Fig. 139, a, and the corresponding expanded diagram is in Fig. 139.6.
Winding diagrams are usually depicted in one projection. To make it easy to distinguish the location of the coils in the slots of the core in the circuits of two-layer windings, the sides of the coils in the slot part are depicted by two adjacent lines - solid and dotted (dash-dotted); The solid line represents the side of the coil laid in the top of the groove, and the dotted line represents the bottom side of the coil laid in the bottom of the groove. The breaks in the vertical lines indicate the numbers of the core grooves. The lower and upper layers of the frontal parts are depicted with dotted and solid lines, respectively. 
Rice. 139. Schemes of a two-layer three-phase winding: a - end, b - unfolded
Arrows on the winding elements, placed on some diagrams, show the direction of the EMF. or currents in the corresponding winding elements at a certain (the same for all phases of the winding) moment in time.
The beginnings of the first, second and third phases are designated C/, C2 and S3, and the ends of these phases are respectively ~C4, C5 and Sb. The diagram indicates the type of winding, as well as its parameters: z - number of slots; 2p - number of poles, y - winding pitch along the slots; a is the number of parallel branches in phase; t - number of phases; Y (star) or D (triangle) - methods of connecting phases.
Schemes and designs of windings.
Stator windings. There are various schemes and designs of stator windings. Below we consider only those that are most often
Rice. 140. Location of the frontal parts of a single-layer winding 
were used in electrical machines old designs and are currently in use.
Single-layer windings, used in machines of old designs, are widely used in modern machines due to their high manufacturability, which allows windings to be wound mechanized - on special winding machines. The total number of coils in a single-layer winding is equal to half the number of stator slots, since one side of the coil occupies the entire slot, and therefore both sides of the coil occupy two slots.
Single layer coils have various shapes, and the frontal parts of the coils of one coil group have the same shape, but different sizes. In order to place the winding in the slots of the stator core, the frontal parts of the coils are placed around the circumference in two or three rows (Fig. 140).
Of the single-layer windings, the most common are concentric two- and three-plane windings. They are called concentric because of the concentric arrangement of the coils of the coil group, and two- and three-plane because of the way the frontal parts of the winding are arranged in two or three levels.
The diagram of a three-phase single-layer concentric two-plane stator winding is shown in Fig. 141, a. There are arrows on the groove lines indicating the directions of the EMF and current in each groove depending on its location under the poles in the magnetic field of the winding at a certain point in time. In a single-layer three-phase winding, the number of coil groups of the entire winding is equal to 3p (ip - the number of groups in each phase).
With an even number of pairs of stator poles (2p = 4, 8, 12, etc.), the number of coil groups will also be even and they can be divided equally into two types; small coil groups - with the frontal parts located in the first plane; large coil groups - with the frontal parts located in the second plane. In this case, the entire two-plane winding can be distributed into three phases with an equal number of small and large coil groups in each phase. If the number of stator pole pairs is odd (2/7 = 6, 10, 14, etc.), the two-plane single-layer winding cannot be phased with the same number of large and small coil groups. One of the coil groups is obtained with skewed frontal parts, since its halves are located in different planes.
Rice. 141. Schemes of stator windings of electrical machines: a - single-layer concentric two-plane, 6 - single-layer two-plane with an adapter coil group, c - two-layer loop
Such a coil group is called a transition group.
The diagram of a single-layer two-plane stator winding of a six-pole machine with an adapter coil group is shown in Fig. 14Cb. The production of single-layer windings with soft coils of round wires and with transition front parts is technologically simple. Winding rigid single-layer coils from rectangular wires is associated with a number of difficulties - the use of special templates and the complexity of molding the frontal parts of the transition group coils. If such a winding is used in a rotor, then due to the different mass (imbalance) of the frontal parts of the winding, balancing of the rotor becomes difficult, and the presence of imbalance causes vibration of the machine.
In double layer winding total number coils is equal to the total number of slots in the stator core, and the total number of coil groups in a phase is the number of poles of the machine. Double-layer windings are made in one or several parallel branches. The diagram of a two-layer loop winding, made in two parallel branches (a = 2) with single-turn coils, is shown in Fig. 141, v. There are no additional inter-coil jumpers, since the inter-coil connections are made directly by the frontal parts.
All coil groups included in any parallel branch are concentrated on one part of the stator circumference, therefore this method of forming parallel branches is called concentrated, in contrast to the distributed method, in which all coil groups are distributed along the entire circumference of the stator by the desire of a parallel branch. To perform a parallel connection in a distributed manner, it is necessary to include in series the odd coil groups (1,7, 13 and 19) of the circuit in the first parallel branch of the first phase, and the even coil groups (4, 10,16 and 2V2) of this circuit in the second parallel branch schemes. The possible number of parallel branches of a two-layer loop winding with an integer number of slots per pole and phase is determined by the ratio of the number of pole pairs to the number of parallel branches, equal to an integer and equal to an integer).
The main advantage of double-layer windings compared to single-layer windings is the ability to choose any shortening of the winding pitch that improves the characteristics of the electric machine:
Rotor windings. The rotors of asynchronous electrical machines are made with a short-circuited or phase winding.
The short-circuited windings of electrical machines of old designs were made in the form of a “squirrel cage”, consisting of copper rods, the ends of which were sealed in holes drilled in copper short-circuit rings (see Fig. 97, a). 
Rice. 142. Wave windings: a - rotor, b - armature
In modern asynchronous electric machines with a power of up to 100 kW, the short-circuited rotor winding is formed by filling its slots with molten aluminum.
In phase rotors of asynchronous electric motors, two-layer wave or loop windings are most often used. The most common are wave windings, the main advantage of which is the minimum number of intergroup connections.
The main element of the wave winding is usually a rod. A two-layer wave winding is made by inserting two rods from the end of the rotor into each of its closed or semi-closed grooves. The diagram of the wave winding of a four-pole rotor with 24 slots is shown in Fig. 142, a. Two rods are placed in each winding groove, and the rods of the upper and lower layers are connected by soldering using clamps placed on the ends of the rods.
The pitch of a wave type winding is equal to the number of slots divided by the number of poles. In the diagram shown in Fig. 142, i, winding pitch along the slots = 24:4 = 6. This means that the upper rod of groove 1 is connected to the lower rod of groove 7, which, with a winding pitch of six, is connected to the upper rod of groove 13 and the lower 19. To continue winding in steps equal to six, it is necessary to connect the lower rod of the groove with the upper groove 7, i.e., close the winding, which is unacceptable. To avoid short-circuiting the winding when approaching the groove from which it began, shorten or lengthen the winding pitch by one groove. Wave windings made with a reduction in pitch by one slot are called windings with shortened transitions, and those made with an increase in pitch by one slot are called windings with extended transitions.
In the winding diagram, the number of slots q per pole and phase is two, so it is necessary to bypass the rotor twice, and to create a four-pole winding there are not enough connections on the opposite side of the rotor, which can be obtained by bypassing it, but in the opposite direction. In wave windings, a distinction is made between the front winding pitch on the side of the leads (slip rings) and the rear winding pitch on the side opposite to the slip rings.
Bypassing the rotor in the opposite direction, in this case the transition to the rear step, is achieved by connecting the lower rod of the groove 18 c. the lower rod, one step away from it. Next, two rounds of the rotor are made. Continuing to go around the rotor with the rear step, the lower rod of groove 12 is connected to. the upper rod of the groove 6. Further connections are made as follows. The lower rod of groove G is connected to the upper rod of groove 19, which (as can be seen from the diagram) is connected to the lower rod of groove 13, and the latter, in turn, to the upper rod of groove 7. The other end of the upper rod of groove 7 goes to the output, making end of the first phase.
Windings of phase rotors asynchronous motors, are connected mainly in a “star” configuration with the three ends of the winding leading out to the slip rings. The terminals of the ends of the rotor winding are designated from the first phase P1, from the second P2 and from the third P39, and the ends of the winding phases are designated P4, P5 and P6, respectively. The jumpers connecting the beginnings and ends of the rotor winding phases are indicated in Roman numerals, for example, in the first phase, the jumper connecting the beginning of P1 and the end of P4 is designated by the numbers I - IV, P2 and P5 - II-V, RZ and P6 - III - VI.
Anchor windings. A simple armature wave winding (Fig. 142.6) is produced by connecting the output ends of the sections to two collector plates AC and BD, the distance between which is determined by double pole division (2t). When making a winding, the end of the last section of the first bypass is connected to the beginning of the section adjacent to the one from which the bypass began, and then the bypasses continue along the armature and collector until all the slots are filled and the winding is closed.
Rice. 143. Machine for manual winding of stator winding coils:
A - general view, b - view from the template side; 1 - template pads, 2 shaft, 3 - disk, 4 - revolution counter, 5 - handle
Winding repair technology.
Long-term practice of operating repaired electrical machines with partially replaced windings has shown that they, as a rule, fail after a short time. This is caused by a number of reasons, including a violation during repair of the integrity of the insulation of the undamaged part of the windings, as well as a discrepancy in the quality and service life of the insulation of the new and old parts of the windings. The most appropriate method when repairing electrical machines with damaged windings is; replacement of the entire winding with full or partial use of its wires. Therefore, this section provides descriptions of repairs in which damaged windings of stators, rotors and armatures are replaced completely with newly manufactured ones at a repair plant.
Repair of stator windings.
The manufacture of the stator winding begins with the preparation of individual coils on a template. To correctly select the template size, you need to know the main dimensions of the coils, mainly their straight and frontal parts. The dimensions of the winding coils of repaired machines can be determined by measuring the old winding.
Coils of stator random windings are wound on simple or universal templates with manual or mechanical drive.
When manually winding coils on a simple template, both of its pads 1 (Fig. 143, e, b) are spread to a distance determined by the dimensions of the winding, and they are secured in the cutouts of disk 3 mounted on shaft 2. Then one end of the winding wire is secured to the template and , rotating handle 5, wind the required number of turns of the coil.
The number of turns in the wound coil is shown by counter 4, installed on the frame of the machine and connected to shaft 2. Having finished winding one coil, transfer the wire to the adjacent template cutout and wind the next coil.
Winding coils by hand on a simple template requires a lot of labor and time. To speed up the winding process, as well as reduce the number of solders and connections, mechanized winding of coils is used on machines with special hinged templates (Fig. 144,a), which allow sequential winding of all coils per one coil group or the entire phase. The kinematic diagram of the machine for mechanized winding of coils is shown in Fig. 144.6.
To wind a coil group on a hinged template with a mechanical drive, insert the end of the wire into the template and turn on the machine. Having wound the required number of turns, the machine automatically stops. To remove the wound spool group, the machine is equipped with a pneumatic cylinder
which, through a rod passing inside the hollow spindle, acts on the hinge mechanism 9 of the template, while the template heads move to the center and the released coil group is easily removed from the template. The finished coil group is placed in the grooves.
Before winding coils or coil groups, you should carefully read the winding calculation note of the electrical machine being repaired, which indicates: power, rated voltage and rotor speed of the electrical machine; type and design features of the winding; the number of turns in the coil and wires in each turn; brand and diameter of the winding wire; winding pitch; number of parallel branches in phase; number of coils in a group; the order of alternating coils; the class of insulation used in terms of heat resistance, as well as various information related to the design and method of manufacturing the winding.
Often, when repairing motor windings, it is necessary to replace missing wires of the required grades and cross-sections with existing wires. For the same reasons, winding a coil with one wire is replaced by winding it with two or more parallel wires, the total cross-section of which is equivalent to the required one. When replacing the wires of the windings of electric motors being repaired, the slot fill factor is first checked (before winding the coils), which should be within 0.7 -. 0.75. If the coefficient is more than 0.75
a - hinge template of the machine, 6 - kinematic diagram; 1 - clamping nut, 2 - locking bar, 3 - hinge bar, 4 - mandrel, 5 - pneumatic cylinder, b-gear, 7 - band brake, 8 - template, 9 - template hinge mechanism, 10 - automatic machine stop engagement mechanism , I - machine switch pedal, 12 - electric motor
Rice. 144. Machine for mechanized winding of coil groups of stator windings: 
laying the winding wires in the grooves will be difficult, and with less than 0.7, the wires will not fit tightly in the grooves and the power of the electric motor will not be fully used.
Rice. 145. Laying loose winding coil wires in the grooves of the core 
The coils of a two-layer winding are placed in the grooves of the core in groups, as they were wound on the template. Distribute the wires in one layer and insert the sides of the coils adjacent to the groove (Fig. 145); the other sides of these coils are left not inserted into the grooves until the lower sides of the coils are laid in all the grooves covered by the winding pitch. The following coils are laid simultaneously with their lower and upper sides. Between the upper and lower sides of the coils, insulating gaskets made of electrical cardboard, bent in the form of brackets, are installed in the grooves, and between the frontal parts - made of varnished fabric or sheets of cardboard with pieces of varnished fabric glued to them.
When repairing electrical machines of old designs with closed slots, it is recommended that before dismantling the winding, it is recommended to take from life its winding data (wire diameter, number of wires in the slot, winding pitch along the slots, etc.), and then make sketches of the frontal parts and mark the stator slots. This data may be necessary when restoring the winding.
Making electrical machine windings with closed slots has a number of features. The groove insulation of such machines is made in the form of sleeves made of electrical cardboard and varnished fabric. To produce sleeves, a steel mandrel 1, which consists of two opposing wedges, is first made according to the dimensions of the machine grooves (Fig. 146). The dimensions of the mandrel should be smaller than the dimensions of the groove by the thickness of the sleeve 2. 
Rice. 146.Method of manufacturing insulating sleeves of electrical machines with closed core grooves:
1 - steel mandrel, 2 - insulating sleeve
Then, according to the size of the old sleeve, blanks from electric cardboard and varnished fabric are cut into a complete set of sleeves and they begin to manufacture them. Heat the mandrel to 80 - 100 °C and tightly wrap it with a workpiece impregnated with varnish. A layer of cotton tape is tightly overlapped over the workpiece. After the time required to cool the mandrel to temperature environment, spread the wedges and remove the finished sleeve. Before winding, insert the sleeves into the grooves of the stator, and then fill them with steel knitting needles, the diameter of which should be 0.05 - OD mm larger than the diameter of the insulated winding wire.
From the coil of winding wire, measure and cut a piece of wire necessary for winding one coil. When using pieces of wire that are too long, winding becomes more difficult, takes more time, and often damages the insulation due to the frequent pulling of the wire through the groove.
Pull winding is a labor-intensive manual job, which is usually performed by two winders located on both sides of the stator (Fig. 147). Before the winding begins, steel spokes are installed in the stator slots in accordance with the diameter and number of winding wires placed in its slots. The winding process consists of the operations of pulling the wire through sleeves inserted into grooves, previously cleaned of dirt and remnants of old insulation, and laying the wire in the grooves and frontal parts. Winding usually begins from the side where the coils will be connected, and is carried out in this sequence. The first wrapper strips the end of the wire to a length that is 10-12 cm longer than the length of the groove, and then, having removed the knitting needle in the first groove, inserts the stripped end of the wire in its place and pushes it until it exits the groove on the opposite side of the core. The second wrapper rolls up the end of the wire protruding from the groove with pliers and pulls it to its side, and then, removing the knitting needle from the corresponding groove, following the step of the winding, inserts the end of the elongated wire in its place and pushes it towards the first wrapper. The further winding process involves repeating the operations described above until the groove is completely filled.
Pulling the wires of the last turns of the coils is difficult, since you have to pull the wire through the filled groove with great force. To make drawing easier, the wires are rubbed with talcum powder. In repair practice, winders often use paraffin instead of talc, which is not recommended, since cotton wire insulation coated with a layer of paraffin does not absorb impregnating varnishes well, as a result of which the conditions for impregnation of the insulation of the groove part of the winding wires worsen, and this can lead to turn short circuits in the repaired winding cars.
When winding coils in pull, the inner coil is wound first, the frontal part of which is laid according to the template, and to wind the remaining coils, spacers made of electrical cardboard are placed on the wound frontal part. These gaskets are necessary to create gaps between the frontal parts that serve for insulation, as well as better cooling of the heads during operation of the machine. 
Rice. 1.47. Winding stator coils of an electric machine with closed core slots
Insulation of the frontal parts of the windings of machines for voltages up to 660 V, intended for operation in a normal environment, is carried out with LES glass tape, with each subsequent layer half-overlapping the previous one. Each coil of the group is wound, starting from the end of the core, in this way. First, tape the part of the insulating sleeve protruding from the groove, and then the part of the coil to the end of the bend. The middles of the group heads are wrapped with a common layer of glass tape, completely overlapping. The end of the tape is secured to the head with adhesive or firmly sewn to it. The winding wires lying in the groove must be firmly held in it, for which groove wedges are used, made mainly from dry beech or birch. Wedges are also made from various insulating materials of appropriate thickness, for example, plastic, textolite or getinax, and are produced on special machines.
The length of the wedge should be 10 - 15 mm greater than the length of the stator core and equal to or 2 - 3 mm less than the length of the slot insulation. The thickness of the wedge depends on the shape of the top of the groove and its filling. Wooden wedges must be at least 2 mm thick. To make wooden wedges moisture resistant, they are boiled for 3-4 hours in drying oil at 120-140 °C, and then dried for 8-10 hours at 100-110 °C.
The wedges are driven into the grooves of small and medium-sized machines using a hammer and a wooden extension, and into the grooves of large machines with a pneumatic hammer. Having finished laying the coils in the stator slots and wedging the windings, assemble the circuit. If the winding phase is wound with separate coils, the assembly of the circuit begins by connecting the coils in series into coil groups.
The beginnings of the phases are taken to be the conclusions of the coil groups coming out of the grooves, which are located near the terminal panel. These leads are bent towards the stator housing and the coil groups of each phase are pre-connected by twisting the ends of the wires of the coil groups, stripped of insulation.
After assembling the winding circuit, the electrical strength of the insulation between the phases and on the housing is checked by applying voltage, as well as the correct connection of the circuit. To check the correct assembly of the circuit, use the simplest method - briefly connect the stator to a 127 or 220 V network, and then apply a steel ball (from a ball bearing) to the surface of its bore and release it. If the ball rotates around the circumference of the bore, the circuit is assembled correctly. This check can also be done using a pinwheel. A tin disc is punched in the center and secured with a nail at the end of a wooden plank so that it can rotate freely, and then the spinner made in this way is placed in the bore of the stator connected to the network. If the circuit is assembled correctly, the disk will rotate.
To check the correct assembly of the circuit and the absence of turn short circuits in the windings of the machines being repaired, the EL-1 apparatus is used (Fig. 148, a), which also serves to locate the groove with short-circuited turns in the windings of stators, rotors and armatures, to check the correct connection of the windings according to the diagram and marking the output ends of phase windings of machines. It has high sensitivity, allowing it to detect the casting of one short-circuited turn for every 2000 turns.
The EL-1 portable device is placed in a metal casing1 with a carrying handle. On the front panel of the device there are control knobs, clamps for connecting the windings under test or devices for finding a groove with short-circuited turns, and a cathode-ray indicator screen. On back wall There is a fuse and a block for connecting the cord and connecting the device to the network.
There are five clips at the bottom of the front panel. The rightmost clamp is used to connect the ground wire, the “Out. imp." - for connecting series-connected windings under test or an exciting electromagnet of a device, the “Signal” clamps. yavl." - to connect a moving electromagnet of a device or connect the midpoint of the windings being tested.
The weight of the device is 10 kg.
Testing of windings using EL-1 is carried out following the instructions supplied with the device. To identify defects, two identical windings or sections are connected to the device, and then voltage pulses are periodically applied from both windings under test using a synchronous switch to the cathode ray tube of the device: if there is no damage in the windings and they are identical, the voltage curves are shown on the screen 
Rice. 148. Electronic apparatus EL-1 for control tests of windings (a) and a device for detecting a groove with short-circuited turns (b)
cathode ray tubes will overlap each other, and if there are defects, they will bifurcate.
To identify the grooves in which the short-circuited turns of the winding are located, use a device with two U-shaped electromagnets for 100 and 2000 turns (Fig. 148.6). A fixed electromagnet coil (100 turns) is connected to the “Out” terminals. imp". device, and the coil of a moving electromagnet (20 turns) - to the “Signal” terminals. phenomenon”, while the middle handle should be placed in the extreme left position “Working with the device”.
When moving both electromagnets of the device from groove to groove along the stator bore, a straight or curved line with small amplitudes will be observed on the screen of the cathode ray tube, indicating the absence of short-circuited turns in the groove, or two curved lines with large amplitudes (inverted relative to each other). friend), indicating the presence of short-circuited turns in the groove. Using these characteristic curves, a groove with short-circuited turns of the stator winding is found. Similarly, by moving both electromagnets of the device along the surface of the phase rotor or armature of a DC machine, grooves with short-circuited turns are found in them.
When performing winding work, along with conventional tools (hammers, knives, pliers), a special tool is used (Fig. 149, a h), which facilitates such work as laying and sealing wires in grooves, trimming insulation protruding from the groove, bending copper winding rods anchors and a number of other winding operations. 
Rice. 149h Set of special tools for wrapping electrical machines:
a - plate, b - “tongue”, c - reverse wedge, d - corner knife, d - drift, f - hatchet, g and h - wrenches for bending rotor rods
Repair of rotor windings.
In wound-rotor asynchronous motors, two main types of windings are common: bobbin and bar. The methods for manufacturing random and drawn coil windings of rotors are almost no different from the methods described above for manufacturing the same stator windings. When manufacturing rotor windings, it is necessary to evenly position the frontal parts of the winding to ensure balanced rotor masses, especially for high-speed electric motors.
In machines with a power of up to 100 kW, rod-type double-layer wave rotor windings are predominantly used. In these windings, made of copper rods, it is not the rods themselves that are damaged, but only their insulation due to frequent and excessive heating, during which the slot insulation of the rotors is often damaged.
When repairing rotors with rod windings, the copper rods of the damaged winding are, as a rule, reused, so the rods are removed from the grooves in such a way as to save each rod and, after restoring the insulation, place it in the same groove in which it was located before disassembly. To do this, the rotor is sketched and notes are made on the following winding elements: bandages - the number and location of bandages, the number of turns and layers of bandage wire, the diameter of the bandage wire and the number of staples (locks), the number of layers and material of the bandage insulation; to the frontal parts - the length of the overhangs, the direction of bending of the rods, the winding steps (front » back), transitions (jumpers), which grooves the beginnings and ends of the phases belong to; groove parts - the dimensions of the rod (insulated and non-insulated), the length of the rod within the groove and the total length of the straight section; insulation - material, size and number of insulation layers of the rods, groove box, gaskets in the groove and frontal parts, design of the winding holder insulation, etc.; balancing weights - their quantity and location; diagram, a sketch of the winding circuit with the numbering of the grooves and an indication of its distinctive features. These sketches and notes must be made especially carefully when repairing machines of older designs.
To remove the rotor winding rods, first unbend the bandage locks and remove the bands; mark (in accordance with the numbering of the grooves in the drawing of the winding diagram) all the grooves, which include the beginnings and ends of the phases, as well as transition jumpers; remove the wedges from the rotor grooves, then unsolder the solders in the heads and remove the connecting clamps.
Using a special key (see Fig. 1\49, h), you should straighten the bent frontal parts of the rods of the upper layer located on the side of the slip rings, remove these rods from the groove, and on each rod you need to knock out the number of the groove and layer, after which in the same remove the rods of the bottom layer in order. Then you should clean the rods from the old insulation, straighten (straighten) them, removing burrs and irregularities, and clean the ends with a wire brush.
At the end of the operation, it is necessary to clean the grooves of the rotor core, winding holders and pressure washers from insulation residues and check the condition of the grooves. If there are any malfunctions, fix them.
The rods removed from the rotor grooves, the insulation of which cannot be removed mechanically, are fired in special furnaces at 600 - 650 ° C, without allowing the firing temperature to exceed 650 ° C, which worsens the electrical and mechanical properties of the copper rods due to burnout. You can also remove insulation from copper rods chemically by immersing them for 30 - 40 minutes in a bath with a 6% sulfuric acid solution. The rods removed from the bath should be washed in an alkaline solution and water, and then wiped with clean napkins and dried. The ends of the rods are tinned with POS 30 or POS 40 solder.
For rods that are free from old insulation and straightened, the insulation is restored; New insulation in terms of heat resistance, method of execution and insulating properties must correspond to the factory design. The groove insulation is also restored by laying insulating spacers on the bottom of the grooves and installing the groove boxes so that their uniform protrusion from the grooves on both sides of the rotor core is ensured.
Upon completion of the preparatory operations, they begin to assemble the winding.
The assembly of the rotor core winding consists of three main types of work - laying the rods in the grooves of the rotor core, bending the frontal part of the rods, and connecting the rods of the upper and lower rows by lacing or welding.
Insulated rods that are reused are supplied into slots with only one curved face. The second ends of these rods are bent using special keys after being placed in the grooves. First, the rods of the bottom row are placed in the grooves, inserting them from the side opposite to the slip rings. Having laid the entire lower row of rods, their straight sections are placed on the bottom of the grooves, and the curved frontal parts are placed on an insulated winding holder. The ends of the curved frontal parts are firmly tied together with a temporary bandage made of... soft steel wire, pressing them tightly against the winding holder. A second temporary wire bandage is wound in the middle of the frontal parts. Temporary bands serve to prevent displacement of the rods during further bending operations.
After securing the rods with temporary bands, they begin bending the frontal parts. The rods are bent using two special keys (see Fig. 1499g,h): first in step and then along the radius, ensuring the required axial extension and their tight fit to the winding holder. To bend the rod, take it in left hand the key (see Fig. 149,g) and put it on the straight part of the rod coming out of the core hole. Holding in right hand key (see Fig. 149; l), put it on the frontal part of the rod with its throat and bring it close to the key shown in Fig. 149,g, and then use the previous key to bend the rod at the required angle.
The straight parts of adjacent rods do not allow the first rods to be bent immediately to the required angle, so the first rod can only be bent by the distance between the rods, the second by double the distance, the third by triple, and so on until the rods are bent, taking two or three winding steps, after which you can bend the rod to the required angle. The last (additionally) to bend are those rods from which bending began.
Using special keys, the ends of the rods are also bent, onto which the connecting clamps will then be put on, after which the temporary bandages are removed and interlayer insulation is applied to the frontal parts, and gaskets are inserted into the grooves between the rods of the upper and lower layers.
The phase rotor of an asynchronous electric motor in the process of assembling the rod winding is proven in Fig. 150. After laying the rods of the lower row, they proceed to installing the rods of the upper row of the winding, inserting them into the grooves on the side opposite to the rotor slip rings. Having laid all the rods of the top row, temporary bandages are placed on them, and their ends are connected with copper wire to check the insulation of the winding (no short circuits to the body).
Rice. 150. Phase rotor of an asynchronous electric motor during the assembly of the rod winding:
1 - rotating device stand, 2 - roller, 3 and 4 - lower and upper rows of rods, 5 - insulation between the upper and lower rows of rods
If the insulation test results are satisfactory, continuing the winding assembly process, bend the ends of the upper rods using techniques similar to those for bending the rods of the lower layer, but in the opposite direction. The curved frontal parts of the upper rods are also secured with two temporary bands.
After laying the rods of the upper and lower rows, the rotor winding is dried at 80-100 °C in an oven or drying cabinet equipped with supply and exhaust ventilation. The dried winding is tested by connecting one electrode from a high-voltage test transformer to any of the rotor rods, and the other to the rotor core or shaft, and, since all the rods were previously connected to each other with copper wire, the insulation of all rods is tested simultaneously.
The final operations in the manufacture of the rod winding of the rotor of the machine being repaired are connecting the rods, driving wedges into the grooves and bandaging the winding.
The rods are connected with tinned clamps placed on their ends, and then soldered with POS 40 solder. The clamps can be made of thin strip copper or thin-walled copper tube required diameter. Self-locking clamps made from copper strip 1 - 1.5 mm thick are also used. One end of such a clamp has a figured protrusion, and the other has a corresponding cutout. When bending the clamp, the protrusion enters the cutout and forms a lock that prevents the clamp from unbending.
The clamps are put (according to the diagram) on the ends of the rods, one copper contact wedge is hammered between them *, and then the connection is soldered with a soldering iron using POS 40 solder, or the ends of the rods of the assembled rotor winding are immersed in a bath of molten solder. In order to save expensive tin-lead solder, they also use electric welding to connect copper rods, but this method has a number of disadvantages, for example, it reduces the maintainability of the machine, since disassembling rods connected by welding requires a lot of labor to separate and clean up the welded areas during subsequent repairs. To increase the reliability of machines, they use jointing of rods by soldering with hard (copper-phosphorus, copper-zinc and others) solders.
*Contact wedges are used to create reliable contact between the ends of the rods, since the layers of the rods are separated by insulation and therefore their ends are not. can fit tightly to each other.
The windings of phase rotors of asynchronous electric motors are connected mainly in a star configuration.
After completing the assembly, soldering and testing of the winding rods and connecting its wires to the slip rings, they begin to bandage the rotor.
When repairing electrical machines with wound rotors, it is sometimes necessary to make new rods. Such a need may be caused by damage not only to the insulation, but also to the winding rods themselves, replacement of an existing damaged coil winding with a rod winding, etc.
The production of new rods requires large-scale bending operations. In large electrical repair shops and electrical repair plants, bending operations of newly manufactured rotor rods are carried out using special devices or bending machines.
A simple pneumatic machine for bending (forming) rotor rods and armatures is shown in Fig. 151, d, b. The molding of rods on this machine is carried out as follows. The workpiece to be molded is placed in the groove of the lower part of the replaceable die, consisting of a movable 5 and a stationary part 6, moving (under the influence of a pneumatic cylinder 9) up and down. The fixed part has a concave, and the movable part has a convex shape of curvature, corresponding to the shape of the curvature of the frontal part of the rod. When the pneumatic crane is turned on, the pneumatic cylinder 9 begins to move, under the action of which the upper half of the stamp bends the frontal part 4 of the rod along the radius, and the levers 3 bend the output end and the grooved part of the workpiece. Levers 3 are driven by leads 2, mounted on a gear wheel 7, which rotates from a rack 8 connected to the rod of the pneumatic cylinder 2. After bending, the rods are isolated.
Rice. 151. Pneumatic mill for bending rotor rods and armatures of electrical machines:
a - general view, 6 - kinematic diagrams 1 and 9 - pneumatic cylinders, 2 - driver, 3 - bending lever, 4 - frontal part of the rod 5 and b - movable and stationary parts of the die, 7 - gear wheel, 8 - rack
To obtain a monolithic rod with precisely specified dimensions, the grooved part of the rod is pressed in special presses. The pressed rods fit tightly into the grooves of the rotor core and at the same time have good heat transfer.
The vast majority of asynchronous electric machines with a power of up to 100 kW are produced by industry with squirrel-cage rotors, in which the windings have the form of a “squirrel cage” made of aluminum by casting.
Damage to a squirrel-cage rotor most often manifests itself in the appearance of cracks and broken rods, and less often in the breakage of fan blades. The appearance of cracks and broken rods are a consequence of violations of the technology of filling the rotor grooves with aluminum, allowed by the manufacturer.
Repairing a rotor with a damaged rod involves refilling it after melting aluminum from the rotor and cleaning the grooves. In small electrical repair shops, the rotor is filled with aluminum in special form- a chill mold (Fig. 152), consisting of the upper 4 and lower 7 halves, in which there are annular grooves and recesses for the formation of short-circuit rings and ventilation blades when pouring.
To prevent aluminum from leaking out of the grooves during pouring, a cast iron detachable jacket 5 is used. Before pouring, the rotor package 6 is assembled onto a technological mandrel 2, and then pressed on a press and locked on the mandrel with a ring 1. 
Rice. 152. Chill for filling a squirrel-cage rotor with aluminum:
1 - ring, 2 - mandrel, 3 - bowl, 4 and 7 - upper and lower halves of the mold, 5 - jacket, 6 - rotor package
In this form assembled package installed in the prepared chill mold. The rotor is filled with molten aluminum through the sprue bowl 3.
After the aluminum has cooled, the chill mold is disassembled. The sprue is separated (using a chisel and hammer) from the rotor, and then the technological mandrel is pressed out on the press.
A rotor installed for casting must have a normally compressed core package, heated to 550-600 °C for better adhesion (adhesion) of aluminum to the steel rotor core package.
At large electrical machine-building and electrical repair plants, squirrel-cage rotors are filled with aluminum by centrifugal or vibration methods, as well as by injection molding
Filling the rotor with aluminum under low pressure is most effective, since the aluminum melt is fed into the mold directly from the furnace, which eliminates the possibility of metal oxidation that occurs with other filling methods.
Another advantage of this method is that when pouring, the mold is filled with aluminum from below and therefore the conditions for removing air from the mold are improved.
The filling process is carried out as follows. Aluminum, cleared of films and gas, is poured into crucible b of furnace 8 (Fig. 153), and the crucible is hermetically sealed. Plastic bag. 4 rotors, mounted on a mandrel 3, are inserted into the stationary part 5 of the mold. The moving part 2 of the mold, going down, further presses the rotor package with the necessary force.
When the pneumatic valve (not shown in the figure) is turned on, compressed air is smoothly supplied through air line 1 to the upper part of the crucible. Pure metal rises up through the metal pipeline 7 and fills the mold.” The rate of rise of the metal can be adjusted by changing the pressure of the compressed air. After the aluminum in the mold has hardened, the pneumatic valve is switched and the upper cavity of the crucible communicates with the atmosphere, the pressure in it drops to normal. 
Rice. 153. Scheme of filling rotors with aluminum using low pressure casting:
1 - air duct 2 and 5 - movable and stationary parts of the mold, 3 - mandrel, 4 - rotor package, b - crucible 7 - metal duct, 8 - furnace
Liquid aluminum from the metal pipe is lowered into the crucible. The mold is opened and the filled rotor is removed from it. The structure of the cast metal with this method is dense, and the quality of the casting is high.
The method of filling the rotor under low pressure is effective, but needs further improvement in order to reduce labor intensity and increase the productivity of the process.
Repair of armature windings.
The main malfunctions of armature windings are electrical breakdown of insulation on the housing or bandage, short circuit between turns and sections, and mechanical damage to soldering. When preparing the armature for repair with replacement of the winding, clean it of dirt and oil, remove the old bands and, having soldered the collector, remove the old winding, having previously recorded all the data necessary for the repair.
In micanite-insulated armatures it is often very difficult to remove the winding sections from the slots. If the sections cannot be removed, heat the armature in an oven to 120-150 ° C, maintaining this temperature for 40 - 50 minutes, and after that they are removed using a thin ground wedge, which is driven between the upper and lower sections to lift the upper sections , and for raising the lower ones - between the lower Section and the bottom of the groove. The grooves of the armature, freed from the winding, are cleaned of remnants of old insulation and processed with files, and then the bottom and walls of the grooves are coated with BT-99 electrical insulating varnish.
In DC machines, rod and template windings of armatures are used. The core windings of the armatures are made similarly to the core windings of the rotors described above. To wind sections of a template winding, use insulated wires, as well as copper busbars insulated with varnished cloth or mycalente.
Template winding sections are wound on universal templates, which allow winding and then stretching of a small section without removing it from the template. Stretching of armature sections of large machines is performed on special mechanically driven machines. Before stretching, the section is held together by temporarily braiding it with cotton tape in one layer to ensure the correct formation of the section when stretched. The coils of template windings are insulated manually, and at large repair enterprises - on special insulating machines. When inserting a template coil, you must ensure its correct position in the groove: the ends of the coil facing the collector, as well as the distance from the edge of the core steel to the transition of the straight (groove) part to the frontal part must be the same. After laying all the coils and checking the correctness of the operations performed, connect the winding wires to the collector plates by soldering using POS 40 solder.
Connecting the armature winding wires to the collector plates by soldering is one of the most important repair operations; Soldering performed poorly causes a local increase in resistance and increased heating of the connection area during operation of the machine, which can lead to its emergency failure.
To perform soldering operations, first protect the armature winding by covering it with sheets of asbestos cardboard, then install the armature with the collector in an inclined position to prevent solder from flowing into the space between the plates during soldering. Next, put the stripped ends of the winding wires into the slots of the plates or cockerels, sprinkle with rosin powder, heat (with the flame of a blowtorch or gas burner) evenly the collector up to 180 - 200 °C and, melting the solder rod with a soldering iron, solder the winding wires to the plates.
The quality of soldering is checked by external inspection, measuring the transition resistance between adjacent pairs of plates, and passing the operating current through the armature winding. 
Rice. 154. Machines for making pole coils:
a - for winding a coil of strip copper, 6 - for insulating / wound coil; 1 - copper busbar, 2 and 4 - micanite and keeper tapes, 3 - template, 5 - pole coil
There should be no frozen drops of solder on the surface of the plates or between them. With high-quality soldering, the contact resistance between all pairs of collector plates should be the same. Passing the rated operating current through the armature winding for 25 - 30 minutes should not cause increased local heating, indicating unsatisfactory soldering.
Repair of pole coils. In DC electric machines coming in for repair, the coils of the additional poles, wound flat or on the edge with a rectangular copper busbar, are most often damaged. It is not the coil's copper bus itself that is damaged, but the insulation between its turns. Repairing a coil comes down to restoring the interturn insulation by rewinding the coil.
The coil is rewound on a winding machine (Fig. 154, a), and then insulated on an insulating machine (Fig. 154,6). The insulated coil is pulled together with cotton tape and pressed, for which an end insulating washer is put on the mandrel, the coil is installed on it and covered with a second washer, and then the coil is compressed on the mandrel and attached to welding transformer, is heated to 120 °C and, additionally compressing it, is finally pressed, after which it is cooled in the pressed position on the mandrel to 25 °C. The cooled coil removed from the mandrel is coated with air-drying varnish and kept for 10-12 hours at -25 °C.
The outer surface of the pressed coil is insulated with asbestos and then micanite tapes and varnished. The finished coil is placed on an additional pole and secured to it with wooden wedges.
Drying and impregnation of windings.
Some insulating materials (electric cardboard, cotton tapes) used in windings are capable of absorbing moisture contained in the environment. Such materials are called hygroscopic. The presence of moisture in electrical insulating materials prevents the deep penetration of impregnating varnishes into the pores and capillaries of the insulating parts when impregnating the windings, so the windings are dried before impregnation.
Drying (before impregnation) of the windings* of stators, rotors and armatures is carried out in special ovens at 105 - 200 °C. Recently, it has been performed using infrared rays, the sources of which are special incandescent lamps.
*Drying of windings before impregnation may not be carried out when the winding is made of wires with moisture-resistant insulation (enameled windings or with fiberglass insulation), and the insulation of the grooves is made of fiberglass or other non-hygroscopic materials similar to it in their electrical insulating properties.
Dried windings are impregnated in special impregnation baths installed in a separate room, which is equipped with supply and exhaust ventilation and necessary means fire extinguishing
Impregnation is carried out by immersing parts of the electrical machine in a bath filled with varnish, so the dimensions of the bath must be designed for the overall dimensions of the machines being repaired. To increase the penetrating ability of the varnish and improve the conditions of impregnation, the baths are equipped with a device for heating the varnish. Baths for impregnation of stators and rotors of large electrical machines are equipped with a pneumatic lever mechanism, which allows you to smoothly and effortlessly open and close the heavy bath lid by turning the handle of the distribution valve.
For impregnation of windings, oil and oil-bitumen impregnating varnishes of air or oven drying are used, and in special cases - organosilicon varnishes. Impregnating varnishes should have low viscosity and high penetrating ability. The varnish should not contain substances that have an aggressive effect on the insulation of wires and windings. Impregnating varnishes must withstand operating temperatures for a long time without losing their insulating properties.
The windings of electrical machines are impregnated 1, 2 or 3 times depending on their operating conditions, electrical strength requirements, environment, operating mode, etc. When impregnating the windings, the viscosity and thickness of the varnish in the bath are continuously checked, since the varnish solvents gradually evaporate and varnishes thicken. At the same time, their ability to penetrate into the insulation of the winding wires located in the grooves of the stator core or rotor is greatly reduced, especially with thick varnishes when dense. laying wires in grooves. Insufficient winding insulation under certain conditions can lead to electrical breakdown of the insulation. To maintain the required thickness of the varnish, solvents are periodically added to the soaking bath.
Windings After impregnation, electrical machines are dried in special chambers with heated air. According to the heating method, drying chambers are distinguished with electric, gas or steam heating, according to the principle of circulation of heated air - with natural or artificial (forced) circulation, according to the operating mode - periodic and continuous.
To reuse the heat of heated air and improve the drying mode in the chambers, a recirculation method is used, in which 50 - 60% of the exhaust hot air is returned to the drying chamber. For drying windings. most electrical repair plants and electrical shops industrial enterprises Electrically heated drying chambers are used.
This chamber is a welded frame structure made of steel mounted on concrete. semi. The walls of the chamber are lined with brick and a layer of slag. The air supplied to the chamber is heated by electric heaters consisting of a set of tubular heating elements. Loading and unloading of the chamber is carried out using a trolley, the movement of which (forward and backward) can be controlled from the control panel. The starting and switching devices of the fan and heating elements of the chamber are interlocked so that heating elements can only be turned on after the fan has started. The movement of air through the heater into the chamber occurs in a closed cycle.
During the first drying period (1 - 2 hours after the start), when the moisture contained in the windings quickly evaporates, the exhaust air is completely released into the atmosphere; During the subsequent drying hours, part of the exhaust heated air, containing small amounts of moisture and solvent vapor, is returned to the chamber. The maximum temperature maintained in the chamber depends on the design and heat resistance class of the insulation, but usually does not exceed 200 °C, and the useful internal volume is determined by the overall dimensions of the electrical machines being repaired.
During drying of the windings, the temperature in the drying chamber and the air leaving the chamber are continuously monitored. The drying time depends on the design and material of the impregnated windings, the overall dimensions of the product, the properties of the impregnating varnish and the solvents used, the drying temperature and the method of air circulation in the drying chamber, and the thermal power of the heater.
The windings are installed in the drying chamber in such a way that they are better washed with hot air. The drying process is divided into heating the windings to remove solvents and. baking varnish film.
When heating the windings to remove the solvent, increasing the temperature to more than 100 -110 °C is undesirable, since partial removal of the varnish from the pores and capillaries can occur, and most importantly, partial baking of the varnish film with incomplete removal of the solvent. This usually causes the film to become porous and makes it difficult to remove residual solvent.
Intensive air exchange accelerates the process of removing solvents from the windings. The air exchange rate is usually selected depending on the design, winding insulation composition, impregnating varnishes and solvents. To reduce the drying time, it is allowed at the second stage of drying the windings, i.e. during baking of the varnish film, to briefly (no more than 5-6 hours) increase the drying temperature of windings with class A insulation to 130-140°C. If the winding cannot be dried (the insulation resistance remains low after several hours of drying), the machine is allowed to cool to a temperature 10-15°C higher than the ambient temperature, and then the winding is dried again. When cooling the machine, make sure that its temperature does not drop to the ambient temperature, otherwise moisture will settle on it and the winding will become damp.
At large electrical repair enterprises, the impregnation and drying processes are combined and mechanized. For. For this purpose, a special impregnation and drying conveyor installation is used.
Winding testing. The main indicators of the quality of winding insulation, which determine the reliability of the operation of an electrical machine, are resistance and dielectric strength. Therefore, in the process of manufacturing the windings of repaired machines, the necessary tests are carried out at each transition from one technological operation to another, as the winding manufacturing operations are completed and moving towards the final stage, the test voltages decrease, approaching the permissible ones provided for by the relevant standards. This is because after performing several separate operations, the insulation resistance may decrease each time. If the test voltages are not reduced at certain stages of the repair, an insulation breakdown may occur at such a moment when the winding is ready, when eliminating the defect will require redoing all the work done previously.
The test voltages must be such that the testing process reveals defective areas of the insulation, but at the same time does not damage its serviceable part. Test voltages during the winding repair process are given in Table. 7.
Table 7. Test voltage during winding repair
Repair process | Test voltage, V, at rated voltage of the machine, V |
||
Making or re-insulating a coil after laying it in grooves and wedges, but before connecting the circuit | |||
The same, after soldering connections and insulating the circuit | |||
Testing a coil not removed from the slots - | |||
Testing the entire winding after connecting the circuit with partial repair of the windings | |||
Note. Test duration 1 min.
The list of winding tests includes measuring the insulation resistance of the windings before impregnation and after impregnation and drying. In addition, the electrical strength of the winding insulation is tested by applying high voltage.
After impregnation and drying, the insulation resistance of the windings of electric motors with voltages up to 660 V, measured with a 1000 V megohmmeter, must be no lower than: 3 MOhm - for the stator winding and 2 MOhm - for the rotor winding (after complete rewinding); 1 MOhm for the stator winding and 0.5 MOhm for the rotor winding (after partial rewinding). The indicated winding insulation resistances are not standardized, but are recommended based on the practice of repair and operation of repaired electrical machines.
All electrical machines after repair must be subjected to appropriate tests. When testing, selecting measuring instruments for them, assembling a measurement circuit, preparing the machine being tested, establishing test methods and standards, as well as evaluating test results, you should be guided by the relevant GOSTs and instructions.
4-6. SOLDERING OF WINDINGS, COLLECTORS, BANDAGES
Connecting conductors by soldering is done using solder. According to the melting temperature, solders are divided into soft (tin - lead) with a melting point of up to 230 ° C and hard (copper - silver) with a melting point of 700 ° C and above. There is also an intermediate group of solders. Among the soft tin-lead For solders, solders of the POS-30-POS-90 grades are used (the number indicates the percentage of tin) with a melting point of 180 ° C. Good results are obtained by soldering with pure tin (melting point 230 ° C), however, due to the scarcity of this metal, soldering with pure tin is carried out only in small quantities. especially
|
For anchor |
For anchor |
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in critical electrical machines in the presence of elevated temperatures.
Cadmium-zinc-silver solders (PKDTs Sr 31) with a melting point of 250 ° C are used for soldering the bandages of machines with class H insulation, and lead-silver solders (PSSr 2.5) with a melting point of 280 ° C are used for soldering the collectors of these cars
Among the hard ones, silver solders are used (P Av 45-70) with a melting temperature of 660-730 ° C and copper-phosphorus (PMF7, MF-3) with a melting temperature of 710-850 ° C. There are a number of requirements for solders: they must in molten form, penetrate well enough into the cracks between the surfaces being soldered, i.e., have sufficient fluidity, should not soften at temperatures as close as possible to the melting temperature, and provide sufficient mechanical strength of the solder at these temperatures. The soldering area should not be fragile. The soldering must have a sufficiently low electrical resistance and, in addition, over time, this resistance, as well as mechanical properties, should not deteriorate due to oxidation and aging.
It should be noted that solders with a high lead content are more prone to oxidation, and copper-phosphorus solders produce slightly more brittle compounds than silver ones.
In order for solder to provide a strong connection to the surfaces, in addition to their cleanliness, it is necessary that there is no film of oxides on them. At soldering temperature, the surfaces of any metal are covered with such a film. Fluxes are used to destroy the oxide film: rosin for soft rations and borax for hard rations. Pickling of soldered surfaces with acid when soldering live parts in electrical machines is not allowed, since acid destroys insulating materials.
Rosin can be used in solid form or in the form of an alcohol solution. Borax is used in the form of a powder or an aqueous solution. Soldering is done with a hot lamp or soldering iron. To speed up soldering, it is advisable to use electric soldering irons. For hard soldering, electrically heated pliers (Fig. 4-20) and graphite jaws are used,
Soft solders are used to solder collectors and bandages of all machines, stator and rotor busbars and connections for machines insulated according to class A with low operating temperatures.
It is recommended to use pure tin solder for soldering commutators and bandages of critical machines where significant overloads are possible. For normal machines, soldering of collectors and bands can be done with POS-30-POS-60 solder with a 30-6E% tin content (GOST 1499-42).
Rice. 4-20. Welding pliers.
Hard solder is used to solder: tires (rods) of windings of machines that have high overheating and are insulated by class B-H, non-insulated windings of squirrel-cage rotors, damper cages, etc. Hard solder is also used to connect copper busbars during the winding of coils. Thin wires are soldered with soft solders to avoid burnout.
Soldering technology soft solders involves the following operations: 1) cleaning the surface of the soldering area; 2) heating the soldering site to a temperature at which the solder melts upon touching the soldering site; 3) generous application of rosin; 4) introducing a stick of solder by pressing it against the gap between the surfaces to be soldered; 5) removing (with a rag) excess solder while hot; 6) cooling and washing off the remaining rosin with alcohol.
For better connection Soldered surfaces are recommended to be pre-tinned.
Soldering of collectors It is done in an inclined position so that the tin does not flow behind the cockerels. Warming up the collector blowtorch must be done very carefully so as not to let go of the plates. The winding is covered with asbestos fabric or
cardboard. For small collectors, it is enough to warm up the cockerels with a soldering iron.
The same applies to soldering wires into tape cockerels (Fig. 4-21). The slot in the plate, the cock and the end of the winding wire must be pre-tinned.
The best results are obtained by soldering the collectors in a bath. In this case, the anchor is installed vertically with the collector down. The end part of the cockerels is placed on an asbestos pad lying on the side of a steel ring. The ring and the collector are heated using electric heating to a temperature of 250 ° C, after which the cockerels are generously coated with rosin and molten tin or solder is poured into the groove between them and the side of the ring.
This soldering method ensures good penetration of tin into all areas to be soldered.
Tin, naturally, should not be poured above the level of the cockerels so that it does not flow into the winding.
To perform soldering using this method, the repair shop must have a heating installation and a set of replacement rings for different collector diameters.
A very convenient method (especially in repair conditions) is the method of heating the cockerels when soldering collectors, according to which the collector is covered with a copper clamp or wire, ensuring good contact with the plates. One end from the welding transformer is connected to this clamp, and the other end is connected to a soldering iron, which is a copper rod with a graphite plate mounted in a handle made of insulating material. By touching the graphite pad to the cockerel, it is heated to the desired temperature.
Rice. 4-21. Soldering cockerels.
Soldering Shin double-layer winding involves preparation, i.e., covering the busbars with a staple and wedging them with a copper wedge (Fig. 4-22). The rotor is given a slight tilt to prevent tin from flowing into the winding.
If the tires have a large cross-section and the bracket is long, then to facilitate soldering of the entire surface, slots are made in the bracket or round holes(Fig. 4-"23). Soldering can only be done well
Rice. 4-22. Preparation
rotor rods
windings for soldering.
Figure 4-23. Bracket with holes.
only in the case that there are no voids left inside the bracket with wedged tires. Otherwise, the solder will leak out and the soldering will be weak.
Soldering bandages after winding them, it consists of uniformly soldering adjacent turns of bandage wire with a thin layer of tin, so that a continuous belt is formed, as it were. In this case, there should be no places where the tin is applied in such a thick layer that it covers the turns of the bandage wire.
Soldering wires Hard solder is produced in the following sequence: 1) preparation of the ends; 2) heating until dark red-crimson; 3) sprinkling with borax until the ends of the wire are completely covered with a layer of molten borax; 4) further heating until the solder melts, after which it is necessary to stop heating; 5) inspection and filing of the soldering area; checking its bending strength. Solder in the form of a leaf is placed between the ends of the wire. For large-section rectangular copper, the joint is made obliquely (angle 65°). The ends are placed in clamps and one is secured tightly, the other loosely. The soldering area is heated with a blowtorch, autogenous torch or electric tongs (Fig. 4-20).
Soldering tires can be produced using similar pliers with carbon jaws. Solder in the form of a leaf is placed under the bracket, which is compressed with pliers. The current is turned on for the short time required to melt the solder.
Good results are obtained by soldering with MF-3 phosphorous copper solder (melting point 720-740° C).
The surfaces to be soldered are cleaned with sandpaper and pressed with electric pliers. By turning on the current, the soldering area is heated to 750-800 ° C, and at the same time the edges of the surfaces to be soldered are coated with solder. Due to the high fluidity of this solder, it is distributed over the entire surface. For better solder spreading, it is advisable to position the junction plane obliquely or vertically.
Soldering aluminum wires and busbars complicated by the fact that aluminum is highly susceptible to oxidation. For soldering aluminum wires to each other and to copper wires special solders have been developed [L. 1] with a melting point of 160-450 ° C, containing mainly zinc, tin and additives: aluminum, copper, silver, cadmium.
Aluminum can be soldered with tin using an ultrasonic soldering iron. Such a soldering iron has, in addition to the heater, a winding powered by a current with a frequency of 20,000 Hz, covering a steel core made of a special alloy. At the same time, the working end of the soldering iron makes high-frequency oscillations that destroy the oxide strips.
The most difficult and important issue in repairing electric motors is determining the suitability of serviceable windings for further work and establishing the type and required scope of repair of faulty windings.
Determination of winding suitability
Typical damage to windings is insulation damage and loss of integrity electrical circuits. The insulation condition is judged by indicators such as insulation resistance, high voltage insulation test results, deviations of the DC resistance values of individual windings (phases, poles, etc.) from each other, from previously measured values or from factory data, as well as by the absence of signs of interturn short circuits in individual parts of the winding. In addition, the assessment takes into account the total operating time of the electric motor without rewinding and its operating conditions.
Determination of the degree of wear of winding insulation is carried out on the basis of various measurements, tests and assessment of the external condition of the insulation. In some cases, the winding insulation in appearance and based on test results has satisfactory results and the engine after repair is put into operation without its repair. However, after working for a short time, the machine breaks down due to an insulation breakdown. Therefore, assessing the degree of wear of the machine insulation is a crucial point in determining the suitability of the windings.
A sign of thermal aging of insulation is its lack of elasticity, fragility, tendency to crack and break under fairly weak mechanical stress. The greatest aging is observed in areas of increased heating, remote from the outer surfaces of the insulation. In this regard, to study the thermal wear of winding insulation, it is necessary to open it locally to its full depth. For the study, small areas are selected, located in the areas of greatest aging of the insulation, but accessible for reliable restoration of the insulation after opening. To ensure the reliability of the study results, there must be several places where the insulation was opened.
When opening, the insulation is examined layer by layer, repeatedly bending the removed sections and examining their surface through a magnifying glass. If necessary, compare identical samples of old and new insulation from the same material. If the insulation breaks, peels off, or develops multiple cracks during such tests, it must be replaced in whole or in part.
Signs of unreliable insulation are also the penetration of oil contaminants into the thickness of the insulation and loose pressing of the winding into the groove, which can cause vibration movements of the conductors or sides of the sections (coils).
To determine winding faults, use special devices. Thus, to identify turn short circuits and breaks in the windings of machines, to check the correct connection of the windings according to the diagram, to mark the output ends of the phase windings of electrical machines, an EL-1 electronic device is used. It allows you to quickly and accurately detect a fault during the manufacturing of windings, as well as after laying them in the grooves; The sensitivity of the device allows you to detect the presence of one short-circuited turn for every 2000 turns.
If only a small part of the windings have faults and damage, then partial repairs are prescribed. However, in this case it must be possible to remove faulty parts of the winding without damaging serviceable sections or coils. Otherwise, a major overhaul with a complete replacement of the winding is more appropriate.
Repair of stator windings
Repair of stator windings is carried out in cases of insulation friction, short circuit between wires of different phases and between turns of the same phase, winding short circuit to the housing, as well as breaks or poor contacts in solder joints of windings or sections. The scope of repair depends on general condition stator and the nature of the fault. After determining the stator malfunction, partial repairs are carried out with the replacement of individual winding coils or a complete rewinding is carried out.
In the stators of asynchronous motors with a power of up to 5 kW of a single series, single-layer random windings are used. The advantages of these windings are that the wires of one coil are laid in each half-closed groove, laying the coils in the grooves is a simple operation, and the groove filling ratio with wires is very high. In the stators of electric machines with a power of 5-100 kW, two-layer random windings are used with a semi-closed groove shape. For asynchronous motors with a power above 100 kW, the windings are made with coils of rectangular wire. Stators of machines with voltages above 660 V windings are wound with rectangular wires.
Rice. 103. Hinged template for winding coils:
1 - clamping nut; 2 - fixing bar; 3 - hinged bar.
The methods of manufacturing and laying stators in the grooves are different for windings made of round or rectangular wires. Coils of round wire are wound on special templates. Manually winding bobbins is time-consuming and labor-intensive. More often, mechanized winding of coils is used on machines with special hinged templates (Fig. 103), with which coils can be wound various sizes. The same templates allow you to wind sequentially all the coils intended for one coil group or for the entire phase.
The windings are made from wires of the brand PELBO (wire enameled with oil-based varnish and covered with one layer of threads of cotton yarn), PEL (wire enameled with oil-based varnish), PBB (wire insulated with two layers of threads of cotton yarn), PELLO (wire insulated with oil varnish and one layer of lavsan threads).
Having wound the coil groups, they are tied with tape and begin to be laid in the grooves. To insulate the windings from the housing in the grooves, groove sleeves are used, which are a single-layer or multi-layer U-shaped bracket made of material selected depending on the insulation class. Thus, for insulation class A, electric cardboard and varnished fabric are used, for heat-resistant windings - flexible micanite or glass micanite.
Production of insulation and laying of soft random winding of an asynchronous electric motor
Algorithm flowchart and technological map repair of the random winding of an asynchronous electric motor is given below.
Winding manufacturing technology:
- Cut a set of strips of insulating material according to the dimensions of the winding data. Fold the cuff over the cut strips on both sides. Make a set of groove sleeves.
- Clean the stator grooves from dust and dirt. Insert groove insulation over the entire length into all grooves.
- Cut a set of strips of insulating material and prepare gaskets to size. Make a set of gaskets for the frontal parts of the windings.
- Place two plates into the groove to protect the wire insulation from damage when laying them. Insert a coil group into the stator bore; straighten the wires with your hands and place them in the grooves. Remove the plates from the groove. Distribute the wires evenly in the groove with a fiber stick. Place an interlayer insulating spacer into the groove. Use a hammer (hatchet) to place the laid coil on the bottom of the groove. For double-layer winding, place the second coil in the groove.
- Use ready-made wedges from plastic materials (PTEF films, etc.) or make wooden ones. Cut wooden blanks to the dimensions of the winding data. Determine their relative humidity and dry to a relative humidity of 8%. Soak wooden wedges in drying oil and dry.
- Place the wedge into the groove and use a hammer to wedge it.
Using needle-nose pliers, cut off the ends of the wedges protruding from the ends of the stator, leaving 5 - 7 mm ends on each side. Cut off the protruding parts of the insulating gaskets. - Place insulating spacers in the frontal parts of the windings between adjacent coils of two groups of different phases laid side by side.
Bend the frontal parts of the winding coils by 15-18° with hammer blows towards the outer diameter of the stator. Observe the smooth bend of the coil wires where they exit the groove.
The procedure for making insulation and laying winding wires may be different. For example, the manufacture of groove sleeves, interlayer spacers, and the manufacture of wooden wedges can be carried out before laying the windings, and then the order of work remains according to this scheme.
In the winding manufacturing technology, some generalizations regarding details have been made.
Rice. 104. Laying and insulating the double-layer stator winding of asynchronous motors:
slot (a) and frontal parts of the winding (b):
1 - wedge; 2, 5 - electric cardboard; 3 - fiberglass; 4 - cotton tape; 6 - cotton stocking.
The coils of a two-layer winding are placed (Fig. 104) in the grooves of the core in groups as they were wound on the template. The coils are laid in the following sequence. The wires are distributed in one layer and those sides of the coils that are adjacent to the groove are inserted. The other sides of the coils are inserted after the lower sides of the coils of all grooves covered by the winding pitch have been inserted. The following coils are laid simultaneously with their lower and upper sides with a gasket in the grooves between the upper and lower sides of the coils of insulating spacers made of electrical cardboard, bent in the form of a bracket. Between the frontal parts of the windings, insulating pads made of varnished fabric or sheets of cardboard with pieces of varnished fabric glued to them are laid.
Rice. 105. Device for driving wedges into grooves
After laying the winding in the grooves, the edges of the groove sleeves are bent and wooden or textolite wedges are driven into the grooves. To protect the wedges 1 from breakage and protect the frontal part of the winding, a device is used (Fig. 105), consisting of a bent sheet steel frame 2, into which a steel rod 3 having the shape and size of a wedge is freely inserted. The wedge is inserted with one end into the groove, the other into the cage and driven with hammer blows on the steel rod. The length of the wedge should be 10 - 20 mm greater than the length of the core and 2 - 3 mm less than the length of the sleeve; Wedge thickness - at least 2 mm. The wedges are boiled in drying oil at a temperature of 120-140 C for 3-4 hours.
After placing the coils in the grooves and wedging the windings, the circuit is assembled, starting with the serial connection of the coils into coil groups. The beginnings of the phases are taken to be the conclusions of the coil groups coming out of the grooves located near the input panel of the electric motor. The terminals of each phase are connected after stripping the ends of the wires.
Having assembled the winding diagram, check the electrical strength of the insulation between the phases and on the housing. The absence of turn short circuits in the winding is determined using the EL-1 apparatus.
Replacing a coil with damaged insulation
Replacing a coil with damaged insulation begins with removing the insulation of the inter-coil connections and bandages that attach the frontal parts of the coils to the bandage rings, then remove the spacers between the frontal parts, unsolder the coil connections and knock out the groove wedges. The coils are heated with direct current to a temperature of 80 - 90 °C. The upper sides of the coils are lifted using wooden wedges, carefully bending them inside the stator and tying them to the frontal parts of the laid coils with keeper tape. After this, the coil with damaged insulation is removed from the grooves. The old insulation is removed and replaced with new.
If the coil wires are burnt out as a result of turn short circuits, it is replaced with a new one wound from the same wire. When repairing windings made from rigid coils, it is possible to save the rectangular winding wires for restoration.
The technology for winding rigid coils is much more complex than loose coils. The wire is wound onto a flat template, and the grooved parts of the coils are stretched to an equal distance between the grooves. The coils have significant elasticity, therefore, to obtain precise dimensions, their grooved parts are pressed, and the frontal parts are straightened. The pressing process involves heating under pressure coils coated with bakelite or glypthal varnish. When heated, the binders soften and fill the pores of the insulating materials, and after cooling they harden and hold the wires of the coils together.
Before laying in the grooves, the coils are straightened using devices. The finished coils are placed in the grooves, heated to a temperature of 75 - 90 ° C and pressed with light blows of a hammer on a wooden sediment strip. The front parts of the coils are also straightened. The lower sides of the frontal parts are tied to the bandage rings with a cord. Gaskets are hammered between the frontal parts. The prepared coils are lowered into the slots, the slots are jammed and the inter-coil connections are connected by soldering.
Repair of rotor windings
In asynchronous motors, the following types of windings are used: “squirrel cages” with the rods filled with aluminum or welded from copper rods, coil and rod. The most widely used are “squirrel cages” filled with aluminum. The winding consists of rods and closing rings on which the fan wings are cast.
To remove a damaged “cage,” use smelting it or dissolving aluminum in a 50% caustic soda solution for 2–3 hours. Fill a new “cage” with molten aluminum at a temperature of 750–780 °C. The rotor is preheated to 400-500 °C to avoid premature solidification of aluminum. If the rotor is weakly pressed before casting, then during casting aluminum can penetrate between the iron sheets and short them, increasing losses in the rotor from eddy currents. It is also unacceptable to press the iron too hard, as breaks of the newly poured rods may occur.
Repairs to copper rod squirrel cages are most often done using old rods. After sawing the connection of the “cage” rods on one side of the rotor, remove the ring, and then do the same operation on the other side of the rotor. Mark the position of the ring relative to the grooves so that the ends of the rods and the old grooves coincide during assembly. The rods are knocked out by carefully hitting the aluminum chocks with a hammer and straightened.
The rods should fit into the grooves with a light blow of a hammer on the textolite tamper. It is recommended to simultaneously insert all the rods into the grooves and tap diametrically opposite rods. The rods are soldered one by one, after preheating the ring to a temperature at which copper-phosphorus solder easily melts when brought to the joint. When soldering, make sure to fill the gaps between the ring and the rod.
In asynchronous motors with a wound rotor, the methods of manufacturing and repairing rotor windings are not much different from the methods of manufacturing and repairing stator windings. The repair begins with removing the winding circuit, fixing the locations of the beginning and ends of the phases on the rotor and the location of the connections between the coil groups. In addition, sketch or record the number and location of the bands, the diameter of the bandage wire and the number of locks; number and location of balancing weights; insulation material, number of layers on the rods, gaskets in the groove, in the frontal parts, etc. Changing the connection diagram during the repair process can lead to imbalance of the rotor. A slight imbalance in the balance, while maintaining the circuit after repair, is eliminated by balancing weights, which are attached to the winding holders of the rotor winding.
After establishing the causes and nature of the malfunction, the issue of partial or complete rewinding of the rotor is decided. The bandage wire is unwound onto a drum. After removing the bandages, solder the solders in the heads and remove the connecting clamps. The frontal parts of the rods of the upper layer are bent from the side of the contact rings and these rods are removed from the groove. Clean the rods from old insulation and straighten them. The grooves of the rotor core and winding holder are cleaned of insulation residues. The straightened rods are insulated, impregnated with varnish and dried. The ends of the rods are tinned with POS-ZO solder. The groove insulation is replaced with a new one, placing boxes and gaskets on the bottom of the grooves with even protrusion from the grooves on both sides of the core. After graduation preparatory work start assembling the rotor windings.
Rice. 106. Laying the rotor winding coil:
a - coil; b - open rotor slot with winding installed.
In a single series A of asynchronous motors with a power of up to 100 kW with a wound rotor, loop double-layer rotor windings made of multi-turn coils are used (Fig. 106, a).
When repairing, the windings are placed in open grooves (Fig. 106, b). The previously removed rotor winding rods are also used. The old insulation is first removed from them and new insulation is applied. In this case, the winding assembly consists of placing the rods in the grooves of the rotor, bending the front part of the rods and connecting the rods of the upper and lower rows by soldering or welding.
After laying all the rods or finished windings, temporary bands are applied to the rods and tested for absence of short circuit to the body; The rotor is dried at a temperature of 80-100 °C in a drying cabinet or oven. After drying, the winding insulation is tested, the rods are connected, the wedges are driven into the grooves and the windings are bandaged.
Often in repair practice, bandages are made of fiberglass and baked together with the winding. The cross-section of a fiberglass bandage is increased by 2 - 3 times relative to the cross-section of a wire bandage. The end turn of fiberglass is attached to the underlying layer during the drying process of the winding during sintering of the thermosetting varnish with which the fiberglass is impregnated. With this bandage design, elements such as locks, brackets and under-bandage insulation are eliminated. The devices and machines for winding fiberglass bandages are the same as for winding wire ones.
Repair of armature windings
Faults in the armature windings of DC machines can be in the form of a connection between the winding and the housing, interturn short circuits, wire breaks, and unsoldering of the ends of the winding from the collector plates.
To repair the winding, the armature is cleaned of dirt and oil, the bandages are removed, the connections to the commutator are unsoldered, and the old winding is removed. To facilitate the removal of the winding from the grooves, the armature is heated at a temperature of 80 - 90 ° C for 1 hour. To lift the upper sections of the coils, a ground wedge is driven into the groove between the coils, and to lift the lower sides of the coils, between the coil and the bottom of the groove. The grooves are cleaned and coated with insulating varnish.
In the armatures of machines with a power of up to 15 kW with a semi-closed slot shape, random windings are used, and for machines of higher power with an open slot shape, coil windings are used. The coils are made of round or rectangular wire. The most widely used are template armature windings made of insulated wires or copper bars insulated with varnished cloth or mica tape.
Sections of the template winding are wound onto a universal boat-shaped template and then stretched, as it must lie in two grooves located around the circumference of the armature. After giving the final shape, the coil is insulated with several layers of tape, soaked twice in insulating varnishes, dried and tinned at the ends of the wires for subsequent soldering in the collector plates.
The insulated coil is placed into the grooves of the armature core. They are secured in them with special wedges and the wires are connected to the collector plates by soldering with POS-30 solder. The wedges are pressed from heat-resistant plastic materials - isoflex-2, trivolterma, PTEF (polyethylene terephthalate) films.
Connecting the ends of the winding by soldering is carried out very carefully, since poor soldering will lead to a local increase in resistance and increased heating of the connection during operation of the machine. The quality of soldering is checked by inspecting the soldering area and measuring the contact resistance, which should be the same between all pairs of collector plates. Then the operating current is passed through the armature winding for 30 minutes. If there are no defects at the joints, there should be no increased local heating.
All work on dismantling bandages, applying bandages made of wire or glass tape on the armatures of DC machines is carried out in the same order as when repairing the windings of phase rotors of asynchronous machines.
Repair of pole coils
Pole coils are called excitation windings, which, according to their purpose, are divided into coils of the main and additional poles of DC machines. The main shunt coils consist of many turns of thin wire, and the series coils have a small number of turns of heavy gauge wire, wound from bare copper bars laid flat or on edge.
After identifying the faulty coil, it is replaced by assembling the coil at the poles. New pole coils are wound on special machines using frames or templates. Pole coils are made by winding insulated wire directly onto an insulated pole, previously cleaned and coated with glypthal varnish. Lacquered fabric is glued to the pole and wrapped in several layers of micafolium impregnated with asbestos varnish. After winding, each layer of micafolia is ironed with a hot iron and wiped with a clean cloth. A layer of varnished fabric is glued onto the last layer of micafolia. Having insulated the pole, put the lower insulating washer on it, wind the coil, put on the upper insulating washer and wedge the coil onto the pole with wooden wedges.
The coils of additional poles are repaired, restoring the insulation of the turns. The coil is cleaned of old insulation and placed on a special mandrel. The insulating material is asbestos paper 0.3 mm thick, cut into frames according to the size of the turns. The number of gaskets must be equal to the number of turns. On both sides they are coated with a thin layer of bakelite or glypthal varnish. The coil turns are spread apart on a mandrel and spacers are placed between them. Then they tighten the coil with cotton tape and press it. The coil is pressed on a metal mandrel, onto which an insulating washer is placed, then the coil is installed, covered with a second washer and the coil is compressed. By heating the welding transformer to 120 C, the coil is further compressed. Cool it in the pressed position to 25 - 30 °C. After removal from the mandrel, the coil is cooled, coated with air-drying varnish and kept at a temperature of 20 - 25 ° C for 10 - 12 hours.
Rice. 107. Options for insulating pole cores and pole coils:
1, 2, 4 - getinax; 3 - cotton tape; 5 - electric cardboard; 6 - textolite.
The outer surface of the coil is insulated (Fig. 107) alternately with asbestos and micanite tapes, secured with taffeta tape, which is then varnished. The coil is placed on an additional pole and wedged with wooden wedges.
Drying, impregnation and testing of windings
The manufactured windings of stators, rotors and armatures are dried in special ovens and drying chambers at a temperature of 105-120 °C. By drying, moisture is removed from hygroscopic insulating materials (electrical cardboard, cotton tapes), which prevents deep penetration of impregnating varnishes into the pores of insulating parts when impregnating the winding.
Drying is carried out in the infrared rays of special electric lamps, or using hot air in drying chambers. After drying, the windings are impregnated with varnishes BT-987, BT-95, BT-99, GF-95 in special impregnation baths. The premises are equipped with supply and exhaust ventilation. Impregnation is carried out in a bath filled with varnish and equipped with heating for better penetration of the varnish into the insulation of the wire winding.
Over time, the varnish in the bath becomes more viscous and thick due to the volatilization of varnish solvents. As a result, their ability to penetrate the insulation of the winding wires is greatly reduced, especially in cases where the winding wires are tightly packed into the grooves of the cores. Therefore, when impregnating the windings, constantly check the thickness and viscosity of the impregnating varnish in the bath and periodically add solvents. The windings are impregnated up to three times depending on their operating conditions.
Rice. 108. Device for impregnation of stators:
1 - tank; 2 - pipe; 3 - pipe; 4 - stator; 5 - cover; 6 - cylinder; 7 - rotary traverse; 8 - column.
To save varnish, which is consumed due to adhesion to the walls of the stator frame, another method of impregnating the winding is used using a special device (Fig. 108). The stator with winding 4, ready for impregnation, is installed on the lid of a special tank 1 with varnish, having previously closed the stator terminal box with a plug. A seal is placed between the end of the stator and the tank cover. In the center of the lid there is a pipe 2, the lower end of which is located below the varnish level in the tank.
To impregnate the stator winding, compressed air with a pressure of 0.45 - 0.5 MPa is supplied to the tank through pipe 3, with the help of which the varnish level is raised until the entire winding is filled, but below the upper part of the edge of the stator frame. At the end of impregnation, turn off the air supply and leave the stator for about 40 minutes (to drain the remaining varnish into the tank), remove the plug from the terminal box. After this, the stator is sent to the drying chamber.
The same device is also used to impregnate the stator windings under pressure. The need for this arises in cases where the wires are laid very tightly in the stator grooves and with normal impregnation (without varnish pressure) the varnish does not penetrate into all the pores of the insulation of the turns. The pressure impregnation process is as follows. Stator 4 is installed in the same way as in the first case, but is closed on top with a lid 5. Compressed air is supplied to tank 1 and cylinder b, which presses the lid 5 to the end of the stator frame through the installed seal gasket. The rotating crossbeam 7, mounted on the column 8, and the screw connection of the cover with the cylinder make it possible to use this device for impregnation of stator windings of various heights.
The impregnating varnish is supplied to the reservoir from a container located in another, non-fire hazardous room. Varnish and solvents are toxic and fire hazardous and, in accordance with labor protection rules, work with them must be carried out in safety glasses, gloves, and a rubber apron in rooms equipped with supply and exhaust ventilation.
After impregnation is completed, the machine windings are dried in special chambers. The air supplied into the chamber by forced circulation is heated by electric heaters, gas or steam heaters. During drying of the windings, the temperature in the drying chamber and the temperature of the air leaving the chamber are continuously monitored. At the beginning of drying the windings, the temperature in the chamber is created slightly lower (100-110 ° C). At this temperature, solvents are removed from the winding insulation and the second drying period begins - baking the varnish film. At this time, the winding drying temperature is increased to 140 °C for 5-6 hours (for insulation class L). If after several hours of drying the insulation resistance of the windings remains insufficient, then turn off the heating and allow the windings to cool to a temperature 10-15 °C higher than the ambient temperature, after which the heating is turned on again and the drying process continues.
The processes of impregnation and drying of windings at energy repair enterprises are combined and, as a rule, mechanized.
In the process of manufacturing and repairing machine windings, the necessary tests of coil insulation are carried out. The test voltage must be such that during testing defective areas of insulation are identified and the insulation of serviceable windings is not damaged. Thus, for coils with a voltage of 400 V, the test voltage of a coil not removed from the grooves for 1 minute should be equal to 1600 V, and after connecting the circuit during partial repair of the winding - 1300 V.
The insulation resistance of electric motor windings with voltages up to 500 V after impregnation and drying must be at least 3 MOhm for the stator windings and 2 MOhm for the rotor windings after complete rewinding and 1 MOhm and 0.5 MOhm, respectively, after partial rewinding. These winding insulation resistance values are recommended based on the practice of repair and operation of repaired electrical machines.
2.12. Repair of electrical machine windings
The winding is one of the most important parts of an electrical machine. The reliability of machines is mainly determined by the quality of the windings, therefore they are subject to requirements for electrical and mechanical strength, heat resistance, moisture resistance, etc. All winding conductors must be insulated from each other and from the machine body. The role of interturn insulation is performed by the insulation of the wire itself, which is applied to it during the manufacturing process at the factory. The insulation that separates the winding conductors from the housing is called housing insulation.
Closed grooves (Fig. 2.22, a) are used in both phase and squirrel-cage rotors of asynchronous motors. In modern machines, closed slots have slots to reduce slot dispersion (these slots cannot be used for laying wires, which is why the slots are called closed). Conductors are placed in such grooves from the end of the core.
Rice. 2.22. :
a - closed; b - semi-closed; e - half-open; g - open with a bandage; d - open with wedge
Semi-closed grooves (Fig. 2.22, b) are used in stators of AC machines with power up to 100 kW and voltage up to 660 V, as well as in rotors and armatures of machines with power up to 15 kW. Winding conductors round section lowered into the grooves one at a time through a narrow slot.
Half-open slots (Fig. 2.22, c) are used in the stators of alternating current machines with a power of 120 - 400 kW and a voltage not exceeding 660 V. Rigid coils are placed in them, two in each layer.
Open grooves with winding fastening with a wire band (Fig. 2.22, d) are used in armatures of DC machines with a power of up to 200 kW.
Open slots with fastening, wedge windings (Fig. 2.22, e) are used in armatures of DC machines with a power of more than 200 kW, rotors of synchronous machines with a power of 15-100 kW, stators of asynchronous machines with a power of over 400 kW and large synchronous machines.
Body insulation can be sleeve or continuous.
With semi-open and open groove forms, the straight part of the wires or coils with sleeve insulation is wrapped in several layers of insulating material, and to fasten the layers they are braided with insulating tapes. With a semi-closed groove shape, sleeves from several layers are placed in the grooves before laying the winding. Sleeve insulation is simple to make and takes up little space in the groove, but it can be used in machines with an operating voltage of no higher than 660 V. This is explained by the fact that at the joints between the sleeves and the tape insulation of the front parts of the coils there can be an insulation breakdown. Therefore, the windings of all machines with voltages above 1000 V have continuous insulation.
In this case, the coils or winding rods are braided with insulating tape along the entire circuit. The tape material is selected depending on the heat resistance class of the winding, the number of layers is determined by the operating voltage of the machine.
There are several ways to wrap conductors and winding coils with insulating tape.
Wrapping the tape staggered (Fig. 2.23, a) - no insulating layer is formed, so this method is used only for tightening the turns of the coil or holding layers of sleeve insulation.
Wrapping tape end-to-end (Fig. 2.23, b) - a continuous layer of insulation is not possible, since there may be bare sections of the coil at the joints. Such insulation is used only to protect the grooved parts of the coil.
IN 
Rice. 2.23. : a - staggered; b - butt; c - overlap
Wrapping tape with an overlap (Fig. 2.23, c) - the main insulation of the coil or rod is formed. In this case, the previous turn of the tape is overlapped by 1/3, 1/2 or 2/3 of its width. Most often, an overlap of 1/2 the width of the tape is used. In this case, the actual insulation thickness is twice as large as the calculated one.
In addition to the interturn and body insulation of the coils, additional insulating gaskets are used in the windings: at the bottom of the groove, between the layers of the windings, under the wire bands, between the frontal parts. These pads are made from electric cardboard, varnish cloth and insulating films, and in machines with heat-resistant insulation from fiberglass, mikafoliya, flexible micanite, etc.
The heat resistance of insulation is one of its most important properties. Depending on this parameter, insulating materials are divided into seven classes: Y (90 °C), A (105 °C), E (120 °C), B (130 °C), F (155 °C), N (180 °C), C (more than 180 °C).
The dielectric properties of insulation are characterized by its electrical strength and the amount of electrical losses. Mica-based materials have high electrical strength. For example, the electrical strength of mica tape, depending on the brand and thickness, is 16 - 20 kV/mm, of unimpregnated cotton tape - only 6, and of glass tape - 4 kV/mm.
The electrical strength of insulating materials can be significantly reduced as a result of deformation during the manufacture of windings. After impregnation with appropriate solutions, the electrical and mechanical strength of some insulating materials increases.
For the windings of electrical machines, wires with fiber, enamel and combined insulation and bare wires of round, rectangular and shaped sections are used.
Round and rectangular enamel-insulated wires are increasingly being used instead of fiber-insulated wires because enamel insulation is thinner than fiber insulation.
The winding of an electric machine consists of turns, coils and coil groups.
A turn is two conductors connected in series, placed under adjacent opposite poles. A turn can consist of several parallel conductors. The number of turns depends on the rated voltage of the machine, and the cross-sectional area of the conductors depends on its current.
A coil is several turns, laid with corresponding sides in two grooves and connected to each other in series. The parts of the coil that lie in the grooves of the cores are called slotted or active, and those located behind the grooves are called frontal.
Coil pitch is the number of slot divisions enclosed between the centers of the slots into which the sides of the turn or coil fit. The coil pitch can be diametrical or shortened. A pitch equal to the pole division is called diametrical, and a pitch slightly smaller than the diametrical pitch is shortened.
A coil group consists of several series-connected coils of the same phase, the sides of which lie under two adjacent poles.
Winding - several coil groups laid in grooves and connected according to a certain pattern.
The windings of electrical machines are divided into loop, wave and combined. Depending on the method of filling the groove, they can be single-layer or two-layer. With a single-layer winding, the side of the coil occupies the entire height of the groove, and with a double-layer winding - only half, the second half is filled by the corresponding side of the other coil.
The main type of stator winding of asynchronous machines is a two-layer winding with a shortened pitch. Single-layer windings are used only in small-sized electric motors.
In Fig. Figure 2.24 shows the unfolded and frontal (end) diagrams of a two-layer three-phase winding. The sides of the coils in the groove part are indicated by two lines - solid and dashed. The solid line represents the side of the coil, which is placed in the upper part of the groove, and the dashed line represents the lower side of the coil, which is placed in the bottom of the groove. The breaks in the vertical lines indicate the numbers of the core grooves. The lower and upper layers of the frontal parts are depicted with dashed and solid lines, respectively.
The beginnings of the first, second and third phases are designated CI, C2, SZ (according to the old but widely used GOST) or Ul, VI, W1 (according to the new GOST), and the ends of these phases are respectively C4, C5, C6 or U2, V2, W2. The diagram indicates the type of winding, and also gives its parameters: z - number of slots; 2p - number of poles; y - winding pitch along the slots; a is the number of pairs of parallel branches in phase; t - number of phases; phase connection method - Y - star, L - triangle.
Stator windings are made of single-layer and double-layer. Winding of single-layer windings is carried out mechanized on special machines.
Single-layer windings have different shapes, and the frontal parts of one coil group have the same shape, but different sizes (Fig. 2.25). To lay the winding in the slots of the stator core, the frontal parts of the coils are placed around the circumference in two or three rows. The most common are single-layer two- and three-plane windings (the frontal parts of the winding are located on two or three levels.
The rotors of asynchronous motors are made with a short-circuited or phase winding. Short-circuited windings of electrical machines of old designs were made in the form of a “squirrel cage” from copper rods, the ends of which were sealed in holes drilled in copper short-circuited rings (see Fig. 2.3). In modern asynchronous electric machines with power up to 100 kW short-circuited winding The rotor is formed by filling its grooves with molten aluminum.
C1 C6 C2 C4 NW C5
Rice. 2.25. (r = 24; p = 2): a - with an even number of pole pairs; b - location of the frontal parts; c - with an odd number of pairs of poles; d - location of the frontal parts
In phase rotors of asynchronous motors, wave or loop windings are most often used. The most common are wave windings, the advantage of which is the minimum number of intergroup connections. The main element of the wave winding is a regular rod. A two-layer wave winding is made by inserting two rods from the end of the rotor into each of its closed or semi-closed grooves. The wave winding diagram of a four-pole rotor, which has 24 slots, is shown in Fig. 2.26, a. The pitch of the wave winding is equal to the number of slots divided by the number of poles. For the circuit shown in Fig. 2.26, a, it will be equal to 6. This means that the upper rod of groove 1 approaches the lower rod of groove 7, which, with a winding pitch of 6, is connected to the upper rod of groove 13 and the lower rod of groove 19. To continue the winding with a pitch equal to 6, it is necessary to connect the lower rod of groove 19 with the upper rod of groove 1, which means short-circuiting the winding, which is unacceptable. To avoid this, shorten or lengthen the winding pitch by one groove. Wave windings with a shortened pitch by one slot are called windings with shortened transitions, and with an increased pitch by one slot - windings with extended transitions.
In the winding diagram, the number of slots per pole and phase is two, so it is necessary to make two bypasses of the rotor, and to form a four-pole winding there are not enough connections on the opposite side of the rotor, which can be obtained by bypassing it, but in the opposite direction.
In wave windings, a distinction is made between the front winding pitch on the side of the leads (slip rings) and the rear winding pitch on the side opposite to the slip rings. Bypassing the rotor in the opposite direction, in this case the transition to the rear step, is achieved by connecting the lower rod of the groove 18 with the lower rod, which lags behind it by one step. Next, two rounds of the rotor are made. Continuing to bypass the rotor backwards, the lower rod of groove 12 is connected to the upper rod of groove 6. Further connections are made in the same way. The lower rod of groove 1 is connected to the upper rod of groove 19, which (as can be seen from the diagram) is connected to the lower rod of groove 13, which in turn is connected to the upper rod of groove 7. The second end of the upper rod of this groove goes to the output, forming the end of the first phase .
The windings of the phase rotors of asynchronous motors are connected mainly by a “star” with the three ends of the winding being connected to the slip rings. The rotor winding terminals are designated PI, P2, РЗ (according to the old GOST) or Kl, LI, Ml (according to the new GOST), and the ends of the winding phases are respectively P4, P5, P6 or K2, L2, M2.
The jumpers that connect the beginnings and ends of the phases of the rotor winding are indicated in Roman numerals, for example, in the first phase, the jumper that connects the beginning of P1 and the end of P4 is designated I-IV, P2 and P5 - II-V, RZ and P6 - III-VI . 
For armatures of DC machines, loop and wave windings are used. A simple armature wave winding (Fig. 2.26, b) is obtained by connecting the output ends of the section with two collector plates AC and BD, the distance between which is determined by double pole division (2t). When making a winding, the end of the last section of the first bypass is connected to the beginning of the section adjacent to the one from which the bypass was started, and then the bypasses continue along the armature and commutator until all the slots are filled and the winding is closed.
Preparing windings for repair. Winding repairs are carried out by specially trained workers at the winding sections of a repair department or enterprise. Preparing machines for repair involves selecting winding wires, insulating, impregnating and auxiliary materials. The list of materials required for winding repair is included in the operational documentation of the electrical machine.
To detect short circuits in the winding between the turns of one coil or wires of different phases, special devices are used. Having determined the nature of the winding malfunction, its repair begins.
The technology for overhauling electrical machine windings includes the following basic operations:
winding disassembly;
cleaning the core grooves from old insulation;
repair of the core and mechanical part of the machine;
cleaning the winding coils from old insulation;
preparatory operations for the manufacture of windings;
production of winding coils;
insulation of the core and winding holders;
laying the winding in the groove;
soldering winding connections;
fastening the winding in the grooves;
drying and impregnation of the winding.
Repair of stator windings. The manufacture of the stator winding begins with winding individual coils on a template. To choose the right template size, you need to know the main dimensions of the coils, mainly their straight and frontal parts. The dimensions of the winding coils of dismantled machines are determined by measuring the old winding.
Coils of stator random windings are usually made on universal templates (Fig. 2.27). This template is a steel plate 1, which is connected to the spindle of the winding machine using a sleeve 2 welded to it. The plate has the shape of a trapezoid. Its slot contains four studs secured with nuts. When winding coils of different lengths, the pins are moved in the slots. When winding coils of different widths, the pins are rearranged from one slot to another.
In the stator windings of AC machines, usually several adjacent coils are connected in series and they form a coil group. To avoid unnecessary solder connections, all coils of one coil group are wound with a single wire. Therefore, rollers 4, machined from textolite or aluminum, are put on the studs 3. The number of grooves on the roller is equal to the largest number of coils in the coil group; the dimensions of the grooves must be such that all the coil conductors can fit into them.
Rice. 2.27.: 1 - plate; 2 - bushing; 3 - hairpin; 4 - rollers
Sometimes when repairing motor windings, it is necessary to replace missing wires with wires of other brands and cross-sections. For the same reasons, instead of winding a coil with one wire, winding with two (or more) parallel wires is used, the total cross-section of which is equivalent to the required one. When replacing the wires of motors being repaired, the slot fill factor is first checked (before winding the coils), which should be 0.7 - 0.75.
The coils of a two-layer winding are placed in the grooves of the core in groups, as they were wound on the template. The wires are distributed in one layer and the sides of the coils are placed, which are adjacent to the groove. The other sides of the coils are not placed in the grooves until the bottom sides of the coils are placed in all the grooves (Fig. 2.28). The following coils are placed with their upper and lower sides simultaneously. Between the upper and lower sides of the coils, insulating gaskets made of electrical cardboard, bent in the form of brackets, are installed in the grooves, and between the frontal parts - made of varnished fabric or sheets of cardboard with pieces of varnished fabric glued to them.
When repairing electrical machines of old designs with closed slots, it is recommended that before dismantling the winding, it is recommended to take its actual winding data (wire diameter, number of wires in the slot, winding pitch along the slots, etc.), and then make sketches of the frontal parts and mark the stator slots (these data may be needed when restoring the winding). 
Rice. 2.28. 
Rice. 2.29. : 1 - steel mandrel; 2 - sleeve
The manufacture of windings with closed slots has a number of features. The groove insulation of such windings is made in the form of sleeves made of electrical cardboard and varnished fabric. First, a steel mandrel 1 is made according to the dimensions of the machine grooves, which consists of two opposing wedges (Fig. 2.29). The mandrel should be smaller than the groove by the thickness of the sleeve 2. Then, according to the dimensions of the old sleeve, blanks from electric cardboard and varnished fabric are cut into a complete set of sleeves and they begin to manufacture them. Heat the mandrel to 80 - 100 °C and tightly wrap it with a workpiece impregnated with varnish. Cotton tape is tightly laid on top of the workpiece with a full overlap. After the mandrel has cooled to ambient temperature, the wedges are spread and the finished sleeve is removed. Before winding, the sleeves are placed in the grooves of the stator, and then filled with steel rods, the diameter of which should be 0.05 - 0.1 mm larger than the diameter of the insulated winding wire. A piece of wire needed to wind one coil is cut from the coil. A long wire complicates winding, and the insulation is often damaged due to frequent pulling it through the groove.
Broach winding is usually carried out by two winders, which are located on both sides of the stator (Fig. 2.30). Frontal insulation
The windings of machines for voltages up to 660 V, intended for operation in a normal environment, are made with LES glass tape, with each subsequent layer semi-overlapping the previous one. Each coil of the group is wound starting from the end of the core. First, tape the part of the insulating sleeve that protrudes from the groove, and then the part of the coil to the end of the bend. The middles of the group heads are completely overlapped with glass tape. The end of the tape is fixed to the head with glue or tightly sewn to it. The winding wires, which lie in the groove, are held using groove wedges made of beech, birch, plastic, textolite or getinax. The wedge should be 10 - 15 mm longer than the core and 2 - 3 mm shorter than the groove insulation and at least 2 mm thick. To ensure moisture resistance, wooden wedges are “cooked” for 3–4 hours in drying oil at 120–140°C.
Rice. 2.30. Pull winding of the stator winding of an electric machine with closed slots
The wedges are driven into the grooves of medium and small machines with a hammer and using a wooden extension, and into the grooves of large machines with a pneumatic hammer (Fig. 2.31). Then the winding circuit is assembled. If the winding phase is wound with separate coils, they are connected in series into coil groups. 
Rice. 2.31. : 1 - wedge; 2 - groove insulation; 3 - extension
The beginning of the phases is taken to be the conclusions of the coil groups, which come out of the grooves located near the terminal panel. These leads are bent to the stator housing and the coil groups of each phase are pre-connected, and the ends of the wires of the coil groups, stripped of insulation, are twisted.
After assembling the winding circuit, check the electrical strength of the insulation between the phases and on the housing, as well as the correctness of its connection. To do this, use the simplest method - briefly connect the stator to the network (127 or 220V), and then apply a steel ball (from a ball bearing) to the surface of its bore and release it. If the ball rotates around the circumference of the bore, then the circuit is assembled correctly. This check can also be carried out using a pinwheel. A hole is punched in the center of the tin disk, secured with a nail at the end of a wooden plank, and then this pinwheel is placed in the stator bore, which is connected to electrical network. If the circuit is assembled correctly, the disk will rotate.
The correct assembly of the circuit and the absence of turn short circuits in the windings of the machines being repaired are also checked using the El-1 electronic device. Two identical windings or sections are connected to the apparatus, and then, using a synchronous switch, periodic voltage pulses are applied to the cathode ray tube of the apparatus. If there is no damage in the windings, the voltage curves on the screen are superimposed on one another, but if there are defects, they bifurcate. To detect grooves in which short-circuited turns are located, use a device with two U-shaped electromagnets for 100 and 2000 turns. The fixed electromagnet coil (100 turns) is connected to the terminals of the device, and the moving electromagnet coil (2000 turns) is connected to the “Signal phenomenon” terminals. In this case, the middle handle should be placed in the extreme left position “Working with the device”. If you move both electromagnets of the device from groove to groove along the stator bore, a straight or curved line with small amplitudes will appear on the screen, which indicates the absence of short-circuited turns in the groove. Otherwise, there will be curved lines with large amplitudes on the screen.
Similarly, short-circuited turns are found in the winding of a phase rotor or armature of DC machines.
Repair of rotor windings. In asynchronous motors with a wound rotor, two main types of windings are used: coil and rod. The manufacture of random and drawn coil windings of rotors is almost no different from the manufacture of the same stator windings.
In machines with a power of up to 100 kW, mainly rod-type double-layer wave rotor windings are used. It is not the rods themselves that are damaged, but their insulation (as a result of frequent excessive heating), as well as the groove insulation of the rotors.
Usually, the copper rods of the damaged winding are reused, so after the insulation is restored, they are placed in the same grooves in which they were before the repair.
The assembly of the rotor core winding consists of three main operations: laying the rods in the grooves of the rotor core, bending the frontal parts of the rods and connecting the rods of the upper and lower rows by soldering or welding. Insulated rods that are reused come into the grooves with only one bent face. The other ends of these rods are bent with special keys after being placed in the grooves. First, the rods of the bottom row are placed in the grooves, inserting them from the side opposite to the slip rings. Having laid the entire lower row of rods, their straight sections are placed on the bottom of the grooves, and the bent front parts are placed on an insulated winding holder. The ends of the bent frontal parts are tightly tightened with a temporary bandage made of soft steel wire, pressing them tightly against the winding holder. A second temporary wire bandage is wound around the middle of the frontal parts. Temporary bandages serve to prevent the rods from shifting during further bending.
The rods are bent using two special keys (Fig. 2.32).
After laying the rods of the lower row, they proceed to laying the rods of the upper row of the winding, inserting them into the grooves on the side opposite to the slip rings. Then temporary bandages are applied. The ends of the rods are connected with copper wire to check that there is no short circuit to the body. If the test results are positive, winding assembly continues, the ends of the upper rods are bent in the opposite direction. The bent frontal parts of the upper rods are also secured with two temporary bands. 
Rice. 2.32. :
o - plate; b - “language”; c - reverse wedge; g - corner knife; d - drift; e - hatchet; ok, a - wrenches for bending rotor rods
After laying the rods of the upper and lower rows, the rotor winding is dried at 80 - 100 ° C in an oven or drying oven. Then the insulation of the dried winding is tested.
The final operations of manufacturing the rod winding of the rotor of the machine being repaired are connecting the rods, driving the wedges into the grooves and banding the winding. To increase the reliability of machines, they use hard soldering to connect rods.
The windings of phase rotors of asynchronous motors are connected mainly by a star.
Most asynchronous motors with a power of up to 100 kW are manufactured with a squirrel-cage rotor, which is made of aluminum by casting.
Repairing a cast rotor with a damaged rod consists of recasting it after smelting the aluminum and cleaning the grooves. Chills are used for this purpose.
At large electrical repair plants, squirrel-cage rotors are filled with aluminum using a centrifugal or vibration method, and injection molding is also used.
Repair of armature windings. The main malfunctions of armature windings: connection of the winding to the housing, interturn short circuits, breaks in the windings, mechanical damage to soldering.
When preparing the armature for repair, the old bands are removed, the connections to the commutator are unsoldered, and the old winding is removed, having previously recorded all the data necessary for the repair.
In DC machines, rod and template windings of armatures are used. The core windings of the armatures are performed in the same way as the core windings of the rotors.
To wind sections of the template winding, insulated wires are used, as well as copper busbars, which are insulated with varnished cloth or mycol tape. Template winding sections are wound on universal templates, which allow you to wind and then stretch a small section without removing it from the template. Stretching of armature sections of large machines is carried out on special machine-driven machines. Before stretching, the section is secured by temporarily wrapping it in a single layer of cotton tape to ensure correct formation sections in tension.
Coils of template windings are insulated manually or on special machines. When laying the template winding in the groove, make sure that the ends of the coil, which are turned towards the collector, as well as the distances from the edge of the core to the transition of the straight (slot) part to the front part are the same. After laying the entire winding, the wires of the armature winding are connected to the collector plates by soldering using POSZO solder.
The quality of soldering is checked by external inspection, measuring the transition resistance between adjacent plates, and passing the operating current through the armature winding. For high-quality soldering, the contact resistance between all pairs of plates must be the same. When passing the rated current through the armature winding for 20 - 30 minutes, local heating should not occur.
Repair of pole coils.
Most often, the coils of additional poles that are wound with a rectangular copper busbar, either plaza or on an edge, are damaged. Usually the insulation between the turns of the coil is damaged. During repairs, the coil is rewound on a winding machine (Fig. 2.33, a), and then insulated on an insulating machine (Fig. 2.33, b). The insulated coil is tied together with cotton tape and pressed. To do this, put an end insulating washer on the mandrel, place the coil on it and cover it with a second washer. Then the coil is compressed on the mandrel, connected to a welding transformer, heated to 120 ° C and, compressing it, pressed again, after which it is cooled in the pressed position on the mandrel to 25 ° C. The cooled coil removed from the mandrel is coated with air-drying varnish and kept for 10 - 12 hours at 20 - 25 °C. 
Rice. 2.33. :
a - for winding coils of strip copper; b - for insulating the wound coil; 1, 4 - micanite and cotton tapes; 2 - template; 3 - copper bus;
5 pole coil
The outer surface of the coil is insulated with asbestos and then micanite tape and varnished. The finished coil is put on an additional pole and secured with wooden wedges.
Drying and impregnation of windings. Some insulating materials (electric cardboard, cotton tapes) are hygroscopic. Therefore, before impregnation, the windings of stators, rotors and armatures are dried in special ovens at 105 - 200 ° C. You can also use infrared rays, the source of which is special incandescent lamps.
The dried windings are impregnated with varnish in special heated baths, which are installed in a separate room equipped with supply and exhaust ventilation and the necessary fire extinguishing equipment.
For windings, impregnating varnishes of air or oven drying are used, and in some cases, organosilicon varnishes. Impregnating varnishes must have low viscosity and high penetrating ability and maintain insulating properties for a long time.
The windings of electrical machines are impregnated once, twice or three times, depending on the operating conditions and the requirements placed on them. During the impregnation process, it is necessary to constantly check the viscosity and thickness of the varnish, as the solvents evaporate and the varnish thickens. At the same time, its ability to penetrate into the insulation of the winding wires located in the grooves of the stator or rotor core is significantly reduced. Therefore, a solvent is periodically added to the impregnation bath.
After impregnation, the windings of electrical machines are dried in special chambers with natural or forced ventilation thermal air. Heating can be electric, gas, steam. Electrically heated drying chambers are the most common.
At the beginning of drying (1 - 2 hours), when the moisture retained in the windings quickly evaporates, the exhaust air is completely released into the atmosphere. During the subsequent drying hours, part of the exhaust warm air, containing a small amount of moisture and solvent vapor, is returned to the chamber. The maximum temperature in the chamber does not exceed 200° C.
During drying of the windings, the temperature in the chamber and the air leaving it is constantly monitored. The windings are positioned so that they are better blown with hot air. The drying process consists of heating the windings (to remove the solvent) and baking the varnish film.
When heating the windings, it is undesirable to increase the temperature above 100 - 110°C, since a varnish film may form prematurely.
During the baking process of the varnish film, it is possible to briefly (no more than 5–6 hours) increase the drying temperature of windings with class A insulation to 130–140 °C.
At large electrical repair enterprises, impregnation and drying are carried out on special impregnation and drying conveyor units.
After repair, electric machines are sent for testing.
1. What methods of winding coils with tapes are used to insulate them?
2. How are insulating materials divided into heat resistance classes?
3. What is a turn, coil, coil group and winding?
4. What types of windings are used in the stators of asynchronous motors?
5. What slots are used in electrical machines?
6. How does the universal winding template work?
7. How is the template winding placed in the slots?
8. How is bar winding made?
9. What devices are used when making armature coils?
10. How are the frontal parts of the windings insulated?
11. What malfunctions occur in pole coils?
12. Why are the windings dried?
13. Winding impregnation process.