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Partial repair of windings of electrical machines. Repair of electric motor windings, their impregnation and drying

Before repair, carefully inspect the windings, paying special attention to the exit points of the winding from the stator slots. The oily places of the windings are wiped with a cleaning cloth soaked in gasoline. Winding places with minor insulation damage (delamination, mechanical damage, wire exposure, etc.) are covered with insulating varnish or air-dried enamel, applying the varnish with a brush or spray gun.

Broken, weakened or lost mechanical strength bandages are carefully removed and bandaged the frontal parts of the windings, using taffeta tape when insulating the winding of heat resistance class A and glass tape when insulating classes E, B and F. The bandage is laid around the circumference of the frontal parts of the winding through one or two grooves using special awl (Fig. 4) with tension. Then the bandages are impregnated with one of the varnishes or air-drying enamels.

The places of the output wires of the motor stator winding with mechanical damage to the insulation are covered with several layers of insulating tape. The lead wires are replaced with new ones if their insulation along the entire length has cracks, delaminations or mechanical damage extending to the copper core. When replacing, the bandage is removed from the frontal part of the winding and the damaged wire is disconnected from the leads of the coil group of the stator winding.

Rice. 4. The tool used in the repair of stator windings of electric motors:

in-awl for bandaging the frontal parts of the windings; b-knife; in -- mandrel for knocking out slot wedges; g - a device for driving slot wedges.

Rice. 5. Connection of output wires with wires of coil groups:

a - twisting of copper wires; b- twisting copper 1 wire with aluminum 2;

c-welding of copper 2 and aluminum 1 wires; G - isolation of the junction with a linoxin tube.

If the motor winding is wound with copper wire, then at a length of 35-40 mm with a knife (Fig. 4, b), the ends of the wires of the coil groups and the lead wire are stripped. The stripped ends are twisted with a twist, as shown in Figure 5a, and the length of the twist should not be less than 20-25 mm. The place of twisting of the wires is soldered with POS-30 or POS-40 solder or welded with a carbon electrode. When welding, one clamp of the transformer is attached to the twist, and the second to the carbon electrode (Fig. 5, c). The arc voltage should be 16-18V.

If the motor winding is made with aluminum wire, then the ends of the wires of the coil groups are stripped at a length of 70-80 mm, and the end of the copper lead wire is stripped at a length of 50 mm. The stripped ends are connected by twisting in such a way that all the strands of the copper wire are inside four or five turns of the aluminum wire and the end of the copper wire protrudes 3-4 mm above the aluminum one (Fig. 5b). Flux is applied to the end surface of the twist with a brush (rosin-25%, ethyl alcohol-75%) and melted with a carbon electrode until a high-quality connection of wires is obtained. Reflow starts from the end surface of the copper wire. After welding, flux residues are removed from the strand.

The junction of the wires is isolated by putting a linoxin tube on the twist (Fig. G) or by winding several layers of electrical tape. Then the frontal parts of the winding are bandaged, placing the turns of the bandage through one or two grooves around the circumference of the frontal part of the winding, and impregnated with air-drying varnish.

Weakened groove wedges are knocked out with a hammer using a mandrel (Fig. 4 in ) and are replaced with new ones made of hard wood (dry beech, birch, etc.). For driving wedges, it is convenient to use a special device consisting of a guide and a guide (Fig. 4, d).

When removing and installing slot wedges, care must be taken not to damage the slot insulation and the insulation of the end windings.

Wedges made on the farm, at the enterprise or received from the manufacturer must be impregnated and dried.

The wedges are impregnated for 3-4 hours in transformer or linseed oil heated to a temperature of 100-120°C, then removed from the oil and allowed to drain for 20-30 minutes. The wedges are dried in a vertical position for 5-6 hours at a temperature of 100-110°C.

After clogging, the ends of the slot wedges protruding beyond the ends of the stator are cut off, leaving 5-7 mm on each side.

To determine the dampening of the insulation of the stator and phase rotor windings, the insulation resistance of the windings relative to the housing and between the windings is measured.

Rice. 6. Measurement of insulation resistance of electric motor windings.

Figure 7 Cabinet for drying windings of electrical machines

If the insulation resistance is less than 1 MΩ at a temperature of 15°C, the motor windings must be dried. It is recommended to dry the windings of electric motors in the conditions of the maintenance site of the electrical equipment of the workshop of the economy or enterprise.

Several drying methods are used. It is most advisable to dry the windings in a drying cabinet at a temperature of 80-90 ° C for 7-10 hours in the site conditions. An OP-4443 cabinet can be used to dry the motor windings (Fig. 7). The cover of the cabinet in the open position serves as a platform for installing electric motors when removed from a crane beam or other lifting device, and the roller table cover and inside the cabinet serves as a platform for supplying motors to the cabinet chamber.

Rice. 8. Scheme of current

drying the insulation of the windings of electrical machines (a):

1- winding; 2 - potential-regulator

The scheme of drying the insulation of the windings of electrical machines by losses in steel (b):

1 - machine stator; 2 - magnetizing winding.

The winding insulation is considered to be dry if its resistance at a steady temperature does not change within 2-3 hours.

When drying the windings at the installation site of electric motors, one of three heating methods is usually used: external heating (thermoradiation method), heating by current passing through the motor windings or induction heating.

For drying windings with external heating, in most cases, infrared radiation lamps of the ZC type with a power of 250, 500, 1000 W, conventional lighting lamps with a power of 100-250 W or tubular electric heaters of the TEN type are used. Lamps and tubular electric heaters are placed in the stator bore so that the winding is heated evenly. During drying, the heating temperature and the insulation resistance of the windings are controlled. The heating temperature is controlled by a thermometer with a scale of 0-150 ° C, and the insulation resistance is controlled by a 500 V megger. At the beginning of drying, the temperature is measured after 15-30 minutes, and after the temperature is established, every hour. The temperature of the winding in the hottest place should not exceed 90 ° C, and the time of heating the windings to a temperature of 70-90 ° C should be at least 2-2.5 hours. For electric motors of the series CX the permissible temperature of the windings during drying is 110°C. To avoid heat dissipation, the stator and rotor should be protected with non-combustible sheets during drying.

When drying with current heating, the motor housing is grounded, the stator windings are connected in series or in parallel (Fig. 8, a) and connected to the secondary winding of a step-down transformer.

Lighting transformers TBS-2 or OSO-0.25 can be used as a step-down transformer for drying the windings of electric motors up to 10 kW, and welding transformers for electric motors of higher power. Before drying, using a rheostat or regulator, the current in the motor windings is set equal to 60-80% of its nominal value. During drying, the heating temperature of the windings and the insulation resistance are controlled.

To avoid insulation breakdown, it is possible to dry by the current method only the windings of electric motors, the insulation resistance of which is at least 0.1 MΩ. It is especially dangerous to dry windings with low insulation resistance with direct current, since during drying, an electrolytic effect of the current may occur.

To dry the windings by induction heating, a magnetizing winding is wound on the stator frame (Fig. 8, b). The motor windings are heated due to heat losses resulting from the heating of the magnetic circuit.

Repair of windings of electrical machines

Preparation of machines for repair consists in the selection of winding wires, insulating, impregnating and auxiliary materials.

The technology of overhaul of the windings of electrical machines includes the following main operations:

winding disassembly;

cleaning the grooves of the core from the old insulation;

repair of the core and the mechanical part of the machine;

cleaning the winding coils from old insulation;

preparatory operations for the manufacture of the winding;

production of winding coils;

insulation of the core and winding holders;

laying the winding in the groove;

soldering winding connections;

fastening of the winding in the grooves;

drying and impregnation of the winding.

Repair of stator windings. The manufacture of the stator winding begins with the winding of individual coils on a template. To correctly select the size of the template, it is necessary to know the main dimensions of the coils, mainly their straight and frontal parts. The dimensions of the winding coils of the dismantled machines are determined by measuring the old winding.

Coils of random stator windings are usually made on universal templates (Fig. 5).

Such a template is a steel plate 1, which, with the help of

the sleeve 2 welded to it is connected to the spindle of the winding machine. The plate has the shape of a trapezoid.

Figure 5 - Universal winding template:

1 - plate; 2 - sleeve; 3 - hairpin; 4 -- rollers

Four studs fixed with nuts are installed in its slot. When winding coils of different lengths, the pins are moved in the slots. When winding coils of different widths, the studs are moved 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 joints, all coils of one coil group are wound with solid 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 conductors of the coil can fit in them.

Coils of a two-layer winding are placed in the grooves of the core in groups, as they were wound on a template. The wires are distributed in one layer and put the sides of the coils that are adjacent to the groove. The other sides of the coils are not placed in the grooves until the lower sides of the coils are laid in all the grooves. The next coils are placed simultaneously with the upper and lower sides.

Between the upper and lower sides of the coils in the grooves, insulating gaskets are installed from electric cardboard bent in the form of a bracket, and between the frontal parts - from varnished cloth or sheets of cardboard with pieces of varnished cloth glued to them.

The insulation of the frontal parts of the winding of machines for voltages up to 660 V, intended for operation in a normal environment, is performed with LES glass tape, with each next layer half-overlapping the previous one. Each coil of the group is wound, starting from the end of the core. First, the part of the insulating sleeve that protrudes from the groove is wrapped with tape, and then the part of the coil to the end of the bend. The middle of the heads of the group is wrapped with glass tape in full overlap. The end of the tape is fixed on the head with glue or sewn tightly to it. The winding wires that lie in the groove are held with the help of groove wedges made of beech, birch, plastic, textolite or getinaks. 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. For moisture resistance, wooden wedges are "boiled" for 3-4 hours in drying oil at 120-140 °C.

Wedges are hammered 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. Then the winding circuit is assembled. If the winding phase is wound with separate coils, they are connected in series into coil groups.

For the beginning of the phases, the conclusions of the coil groups are taken, which come out of the grooves located near the terminal board. These conclusions are bent to the stator housing and the coil groups of each phase are preliminarily connected, the ends of the wires of the coil groups stripped of insulation are twisted.

After assembling the winding circuit, the dielectric strength of the insulation between the phases and on the case is checked, as well as the correctness of its connection. To do this, use the simplest method - briefly connect the stator to the network (127 or 220 V), 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. Such a check can also be carried out using a turntable. A hole is punched in the center of the tin disc, fixed with a nail at the end of a wooden plank, and then this spinner is placed in the bore of the stator, which is connected to the electrical network. If the circuit is assembled correctly, the disc will spin.

Banding of rotors and anchors

When the rotors and armatures of electrical machines rotate, centrifugal forces arise, tending to push the winding out of the grooves and bend its frontal parts. To counteract centrifugal forces and keep the winding in the grooves, wedging and shrouding of the windings of the rotors and armatures is used.

The application of the winding fastening method (wedges or bandages) depends on the shape of the rotor or armature slots. With an open shape of the grooves, bandages or wedges are used. The grooved parts of the windings in the cores of the armatures and rotors are fixed with wedges or bandages made of steel bandage wire or glass tape, and also with wedges and bandages at the same time; the frontal parts of the windings of the rotors and anchors - bandages. Reliable fastening of the windings is important, since it is necessary to counteract not only centrifugal forces, but also the dynamic forces that the windings are subjected to with rare changes in current. For shrouding the rotors, tinned steel wire with a diameter of 0.8-2 mm is used, which has a high tensile strength.

Before winding the bandages, the frontal parts of the winding are upset by hammer blows through a wooden spacer so that they are evenly located around the circumference. When shrouding the rotor, the space under the shrouds is preliminarily covered with strips of electric cardboard to create an insulating gasket between the rotor core and the shroud, protruding by 1-2 mm on both sides of the shroud. The entire bandage is wound with one piece of wire, without rations. On the frontal parts of the winding, in order to avoid swelling, coils of wire are applied from the middle of the rotor to its ends. If the rotor has special grooves, the bandage wires and locks should not protrude above the grooves, and in the absence of grooves, the thickness and location of the bandages should be the same as they were before the repair. Brackets mounted on the rotor should be placed over the teeth, not over the grooves, and the width of each of them should be less than the width of the top of the tooth. The brackets on the bandages are evenly spaced around the circumference of the rotors with a distance between them of no more than 160 mm. The distance between two adjacent bandages should be 200-260 mm. The beginning and end of the binding wire are closed with two lock brackets 10-15 mm wide, which are installed at a distance of 10-30 mm from one another. The edges of the brackets are wrapped around the turns of the bandage and. soldered with POS 40 solder.

To increase the strength and prevent their destruction by centrifugal forces created by the mass of the winding during the rotation of the rotor, fully wound bandages are soldered over the entire surface with POS 30 or POS 40 solder. . In repair practice, wire bandages are often replaced with glass tapes made of unidirectional (in the longitudinal direction) glass fiber impregnated with thermosetting varnishes. For winding bandages made of glass tape, the same equipment is used as for banding with steel wire, but supplemented with devices c. the form of tension rollers and tape handlers.

In contrast to bandaging with steel wire, the rotor is heated up to 100 °C before winding bandages made of glass tape. Such heating is necessary because when a bandage is applied to a cold rotor, the residual stress in the bandage during its baking decreases more than when a heated one is bandaged. The cross section of the bandage made of glass tape must be at least 2 times greater than the section of the corresponding bandage made of wire. The fastening of the last turn of the glass tape with the underlying layer occurs during the drying of the winding during sintering of the thermosetting varnish with which the glass tape is impregnated. When shrouding the windings of the rotors with glass tape, locks, brackets and underband insulation are not used, which is an advantage of this method.

Balancing rotors and armatures

Repaired rotors and armatures of electrical machines are subjected to static and, if necessary, dynamic balancing as an assembly with fans and other rotating parts. Balancing is carried out on special machines to detect imbalance (imbalance) of the masses of the rotor or armature, which is a common cause of vibration during machine operation.

The rotor and armature consist of a large number of parts and therefore the distribution of masses in them cannot be strictly uniform. The reasons for the uneven distribution of masses are the different thickness or mass of individual parts, the presence of shells in them, unequal, the departure of the frontal parts of the winding, etc. Each of the parts included in the assembled rotor or armature may be unbalanced due to the displacement of its axes of inertia from the axis rotation. In the assembled rotor and armature, unbalanced masses of individual parts, depending on their location, can be summed up or mutually compensated. Rotors and armatures, in which the main central axis of inertia does not coincide with the axis of rotation, are called unbalanced.

Unbalance, as a rule, consists of the sum of two imbalances - static and dynamic. The rotation of a statically and dynamically unbalanced rotor and armature causes vibration that can destroy the bearings and foundation of the machine. The destructive effect of unbalanced rotors and armatures is eliminated by balancing them, which consists in determining the size and location of the unbalanced mass. Unbalance is determined by static or dynamic balancing. The choice of balancing method depends on the required balancing accuracy, which can be achieved with the existing equipment. With dynamic balancing, better results of imbalance compensation (less residual imbalance) are obtained than with static balancing.

To determine the imbalance, the rotor is unbalanced with a slight push. An unbalanced rotor (anchor) will tend to return to a position in which its heavy side is at the bottom. After the rotor stops, mark with chalk the place that is in the upper position. The reception is repeated several times to check whether the rotor (armature) always stops in this position. Stopping the rotor in the same position indicates a shift in the center of gravity.

In the place reserved for balancing weights (most often this is the inner diameter of the pressure washer rim), test weights are installed, attaching them with putty. After that, the balancing procedure is repeated. By adding or decreasing the mass of loads, the rotor is stopped in any, arbitrarily taken position. This means that the rotor is statically balanced, i.e. its center of gravity is aligned with the axis of rotation. At the end of balancing, the test weights are replaced with one of the same section and mass, equal to the mass of the test weights and putty and the part of the electrode reduced by the mass, which will be used for welding the permanent load. Unbalance can be compensated for by drilling out an appropriate piece of metal from the heavy side of the rotor.

More accurate than on prisms and disks is balancing on special scales. The balanced rotor is mounted with the shaft journals on the frame supports, which can be rotated around its axis by a certain angle. By turning the balanced rotor, the highest indication of the indicator J is achieved, which will be provided that the center of gravity of the rotor is located.

By adding an additional load to the load - a frame with divisions, the rotor is balanced, which is determined by the indicator arrow. At the moment of balancing, the arrow is aligned with the zero division.

If the rotor is rotated by 180, its center of gravity will approach the swing axis of the frame by a double eccentricity of the displacement of the center of gravity of the rotor relative to its axis. This moment is judged by the lowest reading of the indicator. The rotor is balanced a second time by moving the weight frame along a ruler with a scale calibrated in grams per centimeter. The magnitude of the imbalance is judged by the readings of the scale of the scales.

Static balancing is used for rotors rotating at a speed not exceeding 1000 rpm. A statically balanced rotor (armature) may have a dynamic imbalance, therefore rotors rotating at a frequency above 1000 rpm are most often subjected to dynamic balancing, in which both types of imbalances are simultaneously eliminated - static and dynamic.

Having secured a constant load, the rotor is subjected to test balancing and, with satisfactory results, is transferred to the assembly department for assembly of the machine.

Assembly and testing of electrical machines Assembly is the final stage of the repair of an electrical machine, during which the rotor is connected to the stator using end shields with bearings and the rest of the machine is assembled. As a rule, the assembly of any machine is carried out in the reverse order of disassembly.

The assembly of the machine is carried out in such a sequence that each installed part gradually brings it closer to the assembled state and at the same time does not cause the need for alterations and repetition of the operation.

Technological sequence of the main assembly

The assembly of the DC machine P-41 (Fig. 6) is carried out as follows. They put the excitation coils on the main poles, install the poles with the coils in the frame 16 according to the markings made during disassembly, and fasten them with bolts. They check the distance between the pole pieces with a template, the distance between opposite poles with a shtihmas.

Figure 6 - DC machine P-41

They put coils on additional poles 13, insert the poles with coils into the frame 16 according to the marking made during disassembly, and fasten them with bolts. The distance between the pole pieces of the main and additional poles is checked with a template, and the distance between opposite additional poles is checked with a pin. Connect the coils of the main and additional poles according to the wiring diagram. The polarity of the main and additional poles is checked, as well as the amount of overhang of the winding 12 located in the core 14 of the armature. The fan is mounted on the shaft 7 according to the notes made during disassembly. Lay grease in the labyrinth grooves. Put on the shaft inner covers 2 and 20 bearings. The ball bearings are heated in an oil bath or by induction and mounted on the shaft using a tool. Lubricate the bearings with grease. The anchor is inserted into the frame using the device. Assemble the traverse 6 together with the brush holders on the fixture and grind the brushes. The traverse with brush holders is screwed to the bearing shield 5 and the brushes are lifted from the brush holder sockets. The rear bearing shield 18 is pushed onto the ball bearing, the anchor is lifted by the end of the shaft and the bearing shield is pushed onto the frame lock. Screw the bolts of the bearing shield into the holes of the end of the frame, without tightening them to failure. The front bearing shield 5 is pushed onto the ball bearing 3. The anchor is lifted and the bearing shield is inserted into the frame lock. Screw the bolts of the bearing shield into the holes of the end of the frame, without tightening them to failure. Check the ease of rotation of the armature, gradually tightening the bolts of the bearing shields. Put on the cover 4 of the ball bearing and tighten the covers 4 and 2 with bolts. Lay grease in the labyrinth grooves. Put on the cover 19 of the ball bearing and fasten the covers 19 and 20 with bolts. Check the ease of rotation of the armature by rotating it by the end of the shaft. Lower the brushes onto the collector. Check the distance between the brushes of different fingers along the circumference of the collector and the shift of the brushes along the length of the collector. Check the distance between the collector and the brush holders. Clamps 7 are assembled on a plate 9 in a box 8 and capacitors 10 are attached to it. The assembled clamp plate is installed on the front end shield 5. Electrical connections are made according to the diagram. Check with probes the distance between the armature and the poles. Lead to the clamps of the power wire from the network. Carry out a trial run of the machine. During the running-in process, the operation of the brushes and bearings is checked. Brushes should work without sparks, bearings - without noise. After finishing the run-in, close the collector hatches with covers. Disconnect the power wires and close the terminal box with a lid. They hand over the assembled car to the master or the controller of the quality control department.

When performing assembly work, the electrician must remember that the rotor of the electric motor, held in a central position by the magnetic field of the stator, must be able to move (“run”) in the axial direction. This is necessary so that the rotor shaft, at the slightest displacement, does not erase the ends of the bearings with its sharpening and does not cause additional forces or friction of the mating parts of the machine. The values of the axial run, depending on the power of the machine, should be: 2.5 - 4 mm with a power of 10 - 40 kW and 4.5 - 6 mm with a power of 50 - 100 kW.

All machines after repair check the heating of the bearings and the absence of extraneous noise in them. For machines with a power of over 50 kW at a speed of more than 1000 rpm and for all machines with a speed of more than 2000 rpm, the magnitude of the vibration is measured.

The gaps between the active steel of the rotor and the stator, measured at four points along the circumference, must be the same. The dimensions of the gaps at diametrically opposite points of the rotor and stator of the asynchronous electric motor, as well as between the midpoints of the main poles and the armature of the DC machine, should not differ by more than ± 10%.

Testing of electrical machines. In repair practice, the following types of tests are mainly encountered: before the start of repair and during it to clarify the nature of the malfunction; newly manufactured machine parts; collected after the repair of the machine.

Tests of the machine assembled after repair are carried out according to the following program:

checking the insulation resistance of all windings relative to the housing and between them;

checking the correctness of the marking of the output ends;

measurement of winding resistance to direct current;

checking the transformation ratio of asynchronous motors with a phase rotor;

conducting an idling experiment; overspeed test; test of interturn insulation; dielectric strength test.

Depending on the nature and extent of the repairs performed, sometimes they are limited to performing only a part of the listed tests. If tests are carried out before repair in order to identify a defect, then it is sufficient to carry out part of the test program.

The program of control tests of asynchronous motors includes:

1) external inspection of the engine and measurements of air gaps between the cores;

2) measurement of the insulation resistance of the windings relative to the body and between the phases of the windings;

3) measurement of the ohmic resistance of the winding in the cold state;

4) determination of the transformation ratio (in machines with a phase rotor);

5) testing the machine at idle;

6) measurement of no-load currents by phases;

7) measurement of starting currents in squirrel-cage motors and determination of the starting current ratio;

8) test of electrical strength of coiled insulation;

9) testing the dielectric strength of insulation relative to the housing and between phases;

10) conducting a short circuit test;

11) heating test when the engine is running under load.

The control test program for synchronous machines includes the same tests, with the exception of paragraphs 4, 7 and 10.

Control tests of DC machines include the following operations:

external inspection and measurement of air gaps between the armature core and the poles;

measurement of insulation resistance of windings relative to the case;

measurement of ohmic resistance of windings in a cold state;

checking the correct installation of brushes on neutrals;

checking the correct connection of the windings of the additional poles with

checking the consistency of the polarities of the coils of series and parallel excitations;

checking the alternation of polarities of the main and additional poles;

testing the machine at idle;

test of electrical strength of coiled insulation;

test of dielectric strength of insulation relative to the housing;

heat test with the machine running under load.

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Identification and troubleshooting of electrical machines

In electrical machines, the following types of malfunctions are possible:

sparking brushes;
winding overheating;
short circuits in windings;
abnormal generator voltage;
position when the generator is not excited;
unacceptable fluctuations in engine speed.

Sparking brushes accompanied by increased heating of the collector and brushes. The reason for this may be contamination of the brushes and the commutator, wear of the brushes, burning of the commutator, loose fit of the springs, jamming of the brushes in the brush holder.

Dirt from the brushes and the collector is removed with compressed air, and in some cases with a rag soaked in gasoline. Worn more than 60% or broken brushes are replaced with new ones. New or poorly lapped brushes are lapped against the commutator. To do this, a strip of sanding paper skins (Fig. 185, a) is pulled several times between the brush and the collector. The sanding paper with the abrasive surface should face the brush. After grinding, the collector and brushes are blown with compressed air.

Do not use emery or carborundum cloth for grinding brushes. For proper lapping of the brushes, the ends of the sanding skin must be bent down (see Fig. 185, a), since when the skin is bent upwards (Fig. 185, b), the edges of the brushes will be sawn off and the active width of the brushes will decrease, which can cause sparking on the collector.

Rice. 185 - Brush lapping patterns: correct (a), incorrect (b)

In the presence of soot, shells and other local defects, the collector is machined on a lathe or ground with fine-grained grinding wheels. The collector must have a polished surface, therefore, after turning and grinding it is polished, as a result of which the scratches resulting from the processing of the collector (with a cutter or stone) are eliminated. Polish the manifold at rated speed (of the motor rotor) using sanding paper No. 00.

To polish the collector, a sanding paper is attached to a wooden block (Fig. 186), which is adjusted exactly to the diameter of the collector; the width of the bar is chosen so that it can fit freely between two adjacent traverses. The block is pressed against the rotating collector. When a smooth surface is obtained, the collector is cleaned and blown with compressed air.

Rice. 186 - Block for polishing the collector

The pressure on the brush created by the brush holder spring must correspond to a certain pressure. To reduce mechanical losses on the collector, it is recommended to set the minimum pressure at which the brushes work without sparking. It should be borne in mind that the higher the rotational speed, the greater the pressure is set so that the brushes work satisfactorily with possible vibrations of the brush holders. The difference in pressure on individual brushes should not exceed 10% of its average value.

The force of pressing the brushes is checked with a dynamometer (1) (Fig. 187), fixed to the brush holder lever (2), which presses the brush (3) to the collector (4). To determine the pressing force, it is necessary to lay a sheet of paper (5) between the brush and the collector and gradually pull back the dynamometer. At the moment of free pulling out of the paper from under the brush, the dynamometer will show the amount of brush pressure on the collector.

Rice. 187 - Measuring the brush pressing force with a dynamometer

The correctness of the installation of the brushes must be checked after each turning of the collector. If the brushes are not in the correct position, the machine will start to spark under partial load. When idling, the car does not spark. As the load increases, an all-round fire can be observed along the collector.

Checking the correct position of the traverse is carried out inductive method with a stationary car. A direct current is supplied to the disconnected excitation winding through a rheostat from the battery. The value of the current in the winding should not exceed approximately 5 ... 10% of the nominal. A 45 ... 60 mV millivoltmeter with zero in the middle of the scale is connected to the armature clamps. At the moments of closing and opening of the excitation current, an electromotive force (emf) is induced in the armature and the arrow of the device deviates in one direction or another, depending on the position of the brushes. With the brushes in the correct position (in neutral), e. d.s. should be equal to zero. The traverse with brushes is moved until the desired position of the brushes is reached. It is recommended to check the correct position of the traverse at various positions of the anchor. The armature should be rotated in the same direction to avoid the influence of the possible movement of the brushes in the brush holders on the instrument readings. The final correct position of the traverse is checked during testing of the machine on the stand.

Besides, causing brush sparks there may be an unequal distance around the circumference of the collector between the brushes of individual brackets. It is necessary to check the position of the brushes on the commutator using paper tape and install the brackets so that the brushes of neighboring brackets are at the same distance around the circumference of the commutator.

Sparking can also be caused by using the wrong brand of carbon brushes (too soft or too hard). When repairing, it is necessary to replace all brushes and install those brands recommended by the manufacturer of electrical machines.

elevated heating (overheating) of windings the electric machine is installed during pre-repair testing. Uniform overheating of the entire machine, in the absence of other signs of a malfunction, indicates its overload. In this case, you should first check whether the actual load corresponds to the rated operation of the machine. Deterioration of ventilation conditions due to blockage of the ventilation ducts of the fan impeller can also cause the machine to overheat.

Damage to the pole windings leads to uneven heating. In the windings of the poles, transitions, the output ends of the coils and the places where the output ends pass through the housing are most often damaged. The most common defects include the short circuit of the windings on the case, breakage or poor contact in the windings, the connection between the turns.

After detecting damage, the windings are rewound. To do this, remove the old winding, clean the grooves from burrs, paint them with varnish and insulate with electric cardboard, pressboard and varnished cloth.

Methods for eliminating defects in the pole windings depend on the nature of the damage. Breakage, as well as poor contact in external places accessible for repair, are eliminated by soldering. To find a short circuit to the body, the defective coil is removed from the pole core and the points of contact with the pole and the frame are examined.

Short circuits in windings poles, if they are not at the output ends, are eliminated by partial or complete rewinding. The coils are unwound from the coil and at the same time inspected. If the insulation of the coils, with the exception of the places of connection with the body or the short circuit between the turns, is not damaged and is in a satisfactory condition, then only the damaged places are insulated, and the coil is not completely rewound.

If damage to the pole windings is caused by wet insulation, dry the coil.

In case of short circuits in the armature winding, the generator is poorly excited, the engine does not develop rated speed, in some cases the armature rotates in jerks. When the generator is excited from an external current source, the armature immediately after connecting the excitation winding heats up and smoke appears. Collector plates connected to a defective armature heating winding burn. In this case, short circuits can occur: parts of the turns of one section and the entire section, between two sections lying in the same groove, in the frontal parts of the winding, between any two points of the winding, for example, in the event of a breakdown of the winding on the housing at two points.

To find the short circuits of the turns of one section, between adjacent collector plates, or between adjacent sections located in the same winding layer, the voltage drop method is used, which does not require special equipment. It is used for both loop and wave windings and is especially useful when checking an armature with equalizing connections. The method consists in the fact that direct current is supplied to two adjacent collector plates (1) (Fig. 188) using probes (2), and the voltage drop on the same pair of collector plates is measured with probes (3). It is convenient to use a storage battery as a current source, which provides a current of 5 ... 10 A through a rheostat connected in series with the armature. and the same current will also be less than on the other pair of plates between which there is no short circuit. It is necessary to check the anchor with the brushes raised.

Rice. 188 - Scheme for finding short circuits between turns and armature windings

Short circuit of the armature or collector winding to the body during operation of the machine is not detected, unless there is a short circuit in one of the wires of the network. In the presence of such a circuit (if the machine body is not isolated from the ground), the short circuit of the winding to the body forms a closed circuit. In the absence of grounding of one of the wires of the network, a closed circuit can form only when the winding is closed to the housing in two places.

You can determine the short circuit of the winding to the case with a megohmmeter or a test lamp (Fig. 189). In the latter case, one end of the lamp is connected to the power source, and the other to the collector, while the armature shaft is connected to the second conductor of the power source. The presence of a connection between the winding and the housing is determined by the ignition of the lamp. With this method, the lamp lights up only with good contact at the junction.

Rice. 189 - Scheme for finding the junction of the armature winding with the body

The current source is connected to the collector in the case of a loop winding at two diametrically opposite points, in the case of a wave winding, to plates located at a distance of half the collector step. One conductor from the millivoltmeter is connected to the armature shaft, and the end of the other alternately touches all the collector plates. If you check the armature with a loop winding, then as you approach the plate connected to the body, the readings of the device decrease. When the end of the conductor from the device comes into contact with the collector plate connected to the housing, the millivoltmeter reading will be zero. The reading will be very small with poor contact, and also when the short to the body is not on the collector plate, but on the section attached to this plate.

Since when checking the entire armature, the highest possible voltage acting on the device may turn out to be equal to the voltage supplied to the armature, it is necessary to use a device with a measurement limit equal to the voltage of the power source. Reducing the deviation of the arrow of the device can be achieved by adjusting the current strength by connecting the device through a rheostat.

The place of a short circuit to the case can be found if you move the sections in turn at the points where the winding exits the grooves and at the same time measure the insulation resistance with a megohmmeter. The movement of the sections creates a change in contact and, consequently, a change in resistance. Instead of a megohmmeter, you can use a test lamp, including it between the collector and the armature shaft. The defect is detected by the flashing of the lamp.

In cases where the above methods do not give results, it is necessary to divide it into parts by desoldering the winding. Dividing the winding into two parts, check each part separately with a megger. Having found a short circuit to the body in one of the halves, the ends of the other are left intact, and the damaged half is again divided into two parts and so on until the section with a short circuit to the body is precisely determined.

Repair damage in a variety of ways. For example, an open or poor contact in the winding (in cockerels and clamps) and the collector is eliminated by soldering the winding in the indicated places; if the break occurred in the conductor itself, then the rod or section is replaced with new ones.

Most often, a short circuit to the body occurs at the exit points of the sections from the grooves. This defect is eliminated by installing small wedges of insulating material (fiber, dry beech) under the section or a gasket, varnished lining made of leteroid, electric cardboard, mica, etc. A short to the body in the groove part of the section is eliminated by re-insulating the entire section or replacing it with a new one . A short to the housing caused by moisture insulation is eliminated by drying. If there is a short circuit to the body in several sections and, in addition, the insulation of other sections is poor, then the entire armature winding is rewound. If the collector is connected to the housing, it must be dismantled and repaired.

A short circuit in the armature winding between non-adjacent sections and, in general, the short circuit of a large number of sections are less common than short circuits within the section itself or between the ends of the sections on the collector. Therefore, before proceeding with the elimination of short circuits, it is necessary to carefully inspect the collector and make sure that there are no connections between its plates.

In the event of a short circuit in a section, it must be replaced, since with this defect, the entire insulation of the section usually becomes unusable. The re-insulation of the fault point can be limited only in case of incomplete contact at the fault point. Long-term operation of the machine with large short-circuited branches can render the entire winding unusable, which will require its complete rewinding.

In asynchronous motors, the following types of faults are possible:

stator overheating;
overheating of the stator and rotor windings;
abnormal engine speed;
abnormal noise in the car.

Stator overheating can be observed when the mains voltage is higher than the nominal. To eliminate this malfunction, it is enough to reduce the mains voltage to the nominal value or improve the ventilation of the engine.

Increased local heating when the motor is idling and the rated mains voltage can be caused by burrs formed during filing or due to contact of the rotor with the stator during engine operation. The fault is eliminated by removing burrs; for this, the closure is processed with a file, the connected steel sheets are separated, varnished with an insulating varnish, followed by air drying.

In AC windings, short circuits are possible between turns of one coil, coils of one phase and coils of different phases. The main sign by which a short circuit can be found in alternating current windings is the increased heating of a part of the coil with short-circuited turns. In some cases, the short-circuited part of the winding can be immediately identified by its appearance - by charred insulation.

To determine a defect in the stator or rotor winding, it is necessary to turn on the stator winding at a reduced voltage (1 / 3 ... 1 / 4 of the nominal) with the rotor open and measure the voltage on the rotor rings, slowly turning the rotor. If the voltages on the rotor rings (in pairs) are not equal to each other and vary depending on the position of the rotor relative to the stator, then this indicates a short circuit in the stator winding. In the event of a short circuit in the rotor winding (with a good stator winding), the voltage between the rotor rings will not be the same and will not change depending on the position of the rotor.

After it is established which of the windings (rotor or stator) has a connection between the turns, the defective phase is determined by the methods discussed above.

If a short circuit occurred between two phases, then the junction is found similarly to the previous one, disconnecting the windings phase by phase. The coils of one of the phases that have a connection are divided into two parts and the presence of connections of each such half with the second phase is checked with a megohmmeter. Then the part that is connected to the other phase is again divided into two parts and each of them is checked again, etc.

Sequential Partitioning Method used when finding a short circuit in windings with parallel branches. In this case, it is necessary to divide the defective phases into parallel branches and first determine between which branches there is a connection, and then apply the method to them. Since short circuits between phases are more often in the frontal parts of the winding or connecting conductors, it is sometimes possible to immediately find the connection point by moving the frontal parts while checking with a megohmmeter.

Overheating of the stator winding can be observed when the motor is overloaded or its normal insulation is broken. Reducing the voltage at the motor terminals below the rated voltage also causes an overload of the motor current. Overheating of the winding will be in case of incorrect connection of the stator windings according to the triangle scheme, and not a star.

The cause of strong local heating of the stator winding can be an inter-turn connection in the winding or a short circuit between two phases. Symptoms of a malfunction: unequal current strength in individual phases, the motor is very buzzing and develops reduced torque.

Winding repair

If interturn short circuits or short circuits to the case are detected, as well as a break in the phases of the stator windings, a partial or complete rewinding of the stator is carried out. To facilitate the extraction of defective coils from the grooves, the stator is heated to 70 ... The stator grooves are cleaned of old insulation, the condition of the steel packages is checked.

Coils are wound with an insulated wire of the appropriate brand on a frame or template. If there is no wire of the required brand, the coil is wound with a wire of a different brand, but of the same insulation class.

The coils are wound on a boat template with a device for fixing the ends of the wires. One of the sides of the template is removable for removing the coil after winding. When winding coils from a thin insulated wire with a large number of turns, automatic and semi-automatic machines are used. These machines are equipped with revolution counters and devices for automatically stopping the machine after winding the required number of turns. The machines have devices for laying between the layers of coils of paper insulating gaskets and layout mechanisms that lay the conductors in the correct rows.

At the end of winding around the perimeter of the coil, a pad of electrical cardboard is laid and the coil is tied at the cutouts in the template. The ends of the wires are cut at the distance indicated on the drawing.

The body insulation of the coils is made of several layers of varnished fabric or mica tape. To give the necessary shape and solidity, the turns of the grooved part of the coil are lubricated with adhesive glyptal or shellac varnish before applying the body insulation. Then the grooved part of the coil is heated in a special heater to 110...120°C, after which it is placed in a mold.

During crimping, the heated adhesive lacquer binders soften and fill the pores of the insulation; when cooled, they harden and hold the coil conductors together. The coils are fastened in the grooves with textolite wedges hammered with a wooden hammer.

Coils embedded in the grooves are connected by soldering or flash welding. Fusion welding is performed through a step-down transformer with a power of 500 ... 600 W and a voltage of 220/24 and 220/12 V and can be used to connect wires with a diameter of 0.8 mm or more. The ends of the wires to be welded are pre-twisted and connected to one of the transformer clamps, a carbon electrode is attached to the other clamp.

In electric motors used on refrigerated rolling stock, winding wires made of copper wire are most widely used. In some types of electric motors, aluminum wires are used, which are significantly inferior to copper wires in terms of mechanical strength and electrical conductivity.

Winding wires are made with fibrous, enamel and combined insulation. The material for fibrous insulation is paper (cable or telephone), cotton yarn, natural and artificial silk (nylon, lavsan), asbestos and glass fibers. They are applied in one or more layers in the form of a winding or braid (stocking). Various organic compounds (polyvinyl acetate, organosilicon resins, etc.) are used for enamel insulation.

Brands of winding wires are conventionally indicated by letters. In some brands, the letter designation is followed by the number "1" or "2": the number "1" indicates the normal thickness of the insulation, the number "2" indicates the reinforced thickness.

Designation of brands of winding wires starts with the letter P (wire). Fibrous insulation is indicated by the letters: B - cotton yarn, W - natural silk, ShK and K - rayon, nylon, C - fiberglass, A - asbestos fiber. The letters O and D indicate the number of layers of insulation (one or two). For aluminum winding wires, the letter A is added to the end of the designation. for example, brand PBD means: winding copper wire with insulation from two layers of cotton yarn.

enamel insulation winding wires are marked as follows: EL - varnish-resistant enamel, EV - high-strength enamel (viniflex), ET - heat-resistant polyester enamel, EVTL - polyurethane enamel, ELR - polyamide-resol enamel. for example, PEL brand means: copper wire coated with varnish-resistant enamel.

Combined insulation is also used, which consists of enamel insulation and insulation of fibrous materials superimposed on top of it. For example, the PELBO brand means: copper wire coated with varnish-resistant enamel and cotton yarn in one layer. Brands of winding wires insulated with fiberglass and impregnated in heat-resistant varnish have the letter K in the designation (for example, wire of the PSDK brand).

Three-phase stator windings of AC machines are conditionally divided into single-layer, when the side of the coil occupies the entire groove, and double-layer, when the side of the coil occupies half the groove in height, i.e., two sides of the coil are laid in each groove.

Double layer windings- the most common types of stator windings for AC machines. When rewinding a two-layer stator winding, the lower sides of the coils of the first phase are first laid in the grooves, while the upper sides remain temporarily raised. Then both sides of the coils of the second and third phases are sequentially placed in the grooves. In this case, one side of the coil is placed in the lower part of the next unfilled groove, and the other side is placed in the upper part of the groove, already half filled with winding.

After laying, the lower and then the upper windings are sealed at the bottom of the groove using a special mandrel and a hammer. An insulating gasket is placed between the lower and upper winding layers, the upper winding layer is covered with insulation and reinforced with a wedge. An electric cardboard is placed between the frontal parts of the phase coils. The stacked coils are connected by soldering, and the joints are isolated. After laying the winding, check the correct connection of the coils.

Collector repair

If tracks are found on the surface of the collector from being actuated by brushes, the collector is machined, ground and polished. For grinding use abrasive wheels, which include pumice soaked in kerosene. Polish manifold wooden concave block, pasted over with glass paper.

In order to avoid the protrusion of micanite gaskets above the surface of the collector, it is tracked. Price promotion consists in the fact that the micanite insulation between the collector plates is cut to a depth of 0.5 ... 1.5 mm, longitudinal tracks are formed on the surface of the collector. Tracking is necessary because micanite is harder than the collector copper, and when the copper plates are worn, the micanite protrudes to the surface of the collector, which impairs the operation of the brushes and the commutation of the machine.

The passage of collectors of machines of low and medium power (converters), undercar generators is carried out manually using a scraper made of a hacksaw blade (Fig. 190). The passage of collectors of high-power machines is carried out on a machine tool with a cutter or a special portable machine with a flexible hose.

Rice. 190 - Road insulation of collectors: 1 - collector; 2 - cutter; 3 - electric motor; 4 - support for longitudinal movement; 5 - vertical movement support; 6 - flywheel; 7 - roller

After milling, the faces of the collector plates are removed with a scraper. Chamfers are removed at an angle of 45 ° with a size of 0.5 mm (Fig. 191) and the collector is thoroughly cleaned of mica and copper residues.

Rice. 191 - Chamfering the manifold plates

Sometimes it is required to excavate one or more copper plates that have significant melting or burnout of copper. The causes of such damage can be short circuits between the plates, breakdown of the micanite plates, breakage of the cockerels in the immediate vicinity of the junction with the plates.

The technical conditions for the repair of electrical machines allow the replacement of no more than five plates. Replacing the collector plates is one of the most difficult repairs; the excavation of even one plate can lead to a violation of the solidity of the collector and the loss of a geometrically correct shape, unless special measures are taken and appropriate devices are not used to fasten the collector when removing the plate. As one of these devices can serve as a tie disc.

The runout of the collector in the repaired machine is measured with an indicator after the armature rotates at rated speed. The runout of the collector should be no more than 0.03 ... 0.04 mm. Exceeding these limits causes strong sparking of the brushes. The causes of collector runout can be eccentricity, ellipticity and protrusion of individual plates when their fastening is loosened. If excessive beating of the collector is detected, the machine is disassembled and the bolts tightening the plates are tightened, first in a cold state, then heated to 100 ... 110 ° C. After that, the surface of the collector is turned, polished and roaded.

The most common damage to the contact rings is as follows: wear (operation) of the contact surface and violation of the insulation of the contact bolts, melting and burning out of the contact surface.

Short-circuited rings with small melted and burnt out areas of the contact surface can be restored by surfacing brass or phosphorous copper on it, followed by machining. Partially worn plates can be restored in the same way.

Restoring the insulation of contact rings with a cold fit on the sleeve is carried out as follows. Inside the set of rings (5) assembled on a stand (6) (Fig. 192), laid with intermediate spacers (4), several layers of electric cardboard (3) 0.1 ... 0.4 mm thick are inserted. So that the insulation layers do not break off during crimping, a split sleeve (2) is inserted inside, rolled from sheet steel with a thickness of 1.5 mm. The sleeve (1) is pressed into the hole of the sleeve on a hydraulic press.

Rice. 192 - Assembly of slip rings

To increase the reliability of cold pressing (fitting), the insulating material must have low shrinkage, i.e. it must be well impregnated and dried.

At hot fit slip rings, in contrast to the above repair method, the sleeve is not pressed into the slip rings, but the slip rings are hot with an interference fit on the insulated sleeve.

For insulating sleeve use molding micanite with a thickness of 0.25 ... 0.35 mm, cut into strips, smeared with shellac or glyptal varnish, dried in air for 0.5 ... 1 h and tightly applied to the sleeve, heated to 80 ... 100 ° C. The strips are applied with a slight overlap until the diameter of the sleeve with the insulation applied to it exceeds the inner diameter of the contact rings by 1.5 ... 2 mm. Then the insulation is wrapped with two or three layers of paper, tightly tightened with a 2-3 mm steel clamp, heated to 120-130 ° C, the clamp bolts are tightened and the insulation is heat-treated for 2-3 hours at 150 ° C - for shellac micanite and at 180 ° C - for glyptal.

After the sleeve has cooled down, the varnish smudges are removed from the insulation and machined. The diameter of the cut insulation must exceed the inner diameter of the contact rings by the amount of tightness.

Contact bolts are insulated with mikafolium or molding micanite 0.2 ... 0.3 mm thick. To do this, the surface of the bolt is cleaned of old insulation, lubricated with glyptal or shellac varnish and dried in air for 0.5 ... 1 hour. The micafolium or micanite strip is also varnished, heated until softened, after which it is tightly applied to the bolt and rolled on a flat, heated surface. Then the bolt insulation is tightly wrapped with two or three layers of keeper tape and subjected to heat treatment for 2...3 hours at the appropriate temperature. After cooling, the keeper tape is removed from the insulation, the insulation is cleaned of irregularities and varnish smudges, processed to the desired size manually or on a machine, and pasted over with one or two layers of electric cardboard.

Brush holders and traverses are carefully inspected, the condition of their insulation and the serviceability of parts of the alkaline apparatus are checked. During repairs, the brushes are completely replaced, replacing them with brushes of brands recommended by the manufacturer of electrical machines. In DC machines, the wrong brand of brushes can cause severe sparking on the commutator.

New brushes rub on the collector.

Lapping brushes manually - a very time-consuming operation, therefore, when replacing brushes, they are ground outside the machine on a special machine (Fig. 193). On the same machine, the correct placement of the brushes around the circumference of the collector is checked. The worm screw (7) mounted on the end of the motor shaft (1) rotates the shaft (3) through the worm wheel (6). The shaft rests on two ball bearings inserted into the capsule (8), and is guided at the top by a bronze bushing pressed into the plate (2). Replaceable mandrels (4) are put on the neck machined in the plate to install the traverses of brush holders of machines of various types. A drum (5) is put on the end of the shaft, the outer diameter of which is 1 mm less than the diameter of the collector. Risks are applied to the drum, according to which the placement of brushes around the circumference of the collector is checked. Then the brushes are removed from the brush holders and the drum is wrapped with glass paper, which is fixed with a tape. The brushes are inserted into the holders, the pressure fingers of the brush holders are lowered onto them and the electric motor is turned on. Brush dust is removed using exhaust ventilation.

Rice. 193 - Machine for grinding brushes

When checking the condition of the brush holder traverse, pay attention to the ease of movement of the pressure fingers when lifting and lowering: in this case, the fingers should not touch the side walls and cutouts of the brush holders. Finger insulation and insulating washers must not be damaged. Check the presence of locking bolts, pin bolts and other fasteners. Faulty parts of the brush holders (current-carrying bolts, screws, pressure fingers, broken and insufficiently rigid springs) are replaced.

When the collector rotates, the brushes vibrate in the holders and wear them out. An increase in the gap between the brush and the brush holder cage leads to a misalignment of the brush in the cage and a violation of its contact with the collector. The developed holes in the body of the brush holders are restored by galvanic method or surfacing with subsequent processing. If recovery is not possible, the clip is replaced with a new one. Restoration of the dimensions of the clip by compression is not allowed.

2.12. Repair of windings of electrical machines

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 the requirements of electrical and mechanical strength, heat resistance, moisture resistance, etc. All winding conductors must be isolated 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 body is called body insulation.
Closed grooves (Fig. 2.22, a) are used both in phase and squirrel-cage rotors of asynchronous motors. In modern machines, closed slots are slotted to reduce slot scattering (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 - half-closed; e - half-open; g - open with a bandage; d - open wedge

Semi-closed slots (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. Round winding conductors are lowered into the grooves one by one through a narrow slot.
Semi-open grooves (Fig. 2.22, c) are used in the stators of AC machines with a power of 120 - 400 kW and a voltage of not more than 660 V. Rigid coils are placed in them, two in each layer.
Open grooves with fastening the winding with a wire bandage (Fig. 2.22, d) are used in anchors of DC machines with a power of up to 200 kW.

Open grooves 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 more than 400 kW and large synchronous machines.
Case insulation can be sleeve or continuous.
With half-open and open forms of the groove, the straight part of the wires or coils with sleeve insulation is wrapped with 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 in execution and takes up little space in the groove, but it can be used in machines with an operating voltage of not more than 660 V. This is due to the fact that at the junctions between the sleeves and the tape insulation of the frontal parts of the coils there may be an insulation breakdown. Therefore, the windings of all machines with voltages above 1000 V are completely insulated.
In this case, the coils or winding rods are braided with insulating tape around 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 with tape in a random pattern (Fig. 2.23, a) - an insulating layer is not formed, therefore this method is used only to tighten the turns of the coil or hold the layers of sleeve insulation.

Tape wrapping end-to-end (Fig. 2.23, b) - a continuous layer of insulation is not obtained, 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.

Rice. 2.23. : a - apart; b - butt; in - overlap

Overlapping tape wrapping (Fig. 2.23, c) - the main insulation of the coil or rod is formed. At the same time, 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 thickness of the insulation is twice 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 bandages, between the frontal parts. These gaskets are made of electrical cardboard, lacquer fabric and insulating films, and in machines with heat-resistant insulation made of fiberglass, mikafolium, flexible micanite, etc.
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), H (180 °С), С (more than 180 °С).

The dielectric properties of insulation are characterized by its electrical strength and 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, unimpregnated cotton tape - only 6, and glass tape - 4 kV / mm.
The electrical strength of insulating materials can be significantly reduced as a result of deformations in the manufacture of windings. After impregnation with appropriate solutions, the electrical and mechanical strength of some insulating materials increases.
For windings of electrical machines, wires with fibrous, enamel and combined insulation and bare wires of round, rectangular and shaped sections are used.
Enameled round and rectangular wires are increasingly being used in place of wires with fiber insulation because enamel insulation is thinner than fiber insulation.
The winding of an electrical machine consists of turns, coils and coil groups.
Coil - two conductors connected in series with each other, placed under adjacent opposite poles. A coil may 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.
Coil - several turns, laid by the 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 - the number of groove divisions enclosed between the centers of the grooves in which the sides of the coil or coil fit. The coil pitch can be diametrical or shortened. Diametral is called a step equal to the pole division, and shortened - a little less than the diametrical.
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. According to the method of filling the groove, they can be single-layer and double-layer. With a single-layer winding, the side of the coil occupies the entire groove along its height, and with a two-layer winding, only half, the second half is filled by the corresponding side of the other coil.
The main type of stator winding in asynchronous machines is a two-layer winding with a shortened pitch. Single-layer windings are used only in electric motors of small dimensions.
On fig. 2.24 shows the unfolded and frontal (end) circuits 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 shows the side of the coil, which is placed in the upper part of the groove, and the dashed line is the lower side of the coil, which is placed on the bottom of the groove. In the gaps of the vertical lines indicate the numbers of the grooves of the core. The lower and upper layers of the frontal parts are depicted respectively by dashed and solid lines.
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 grooves; 2p - number of poles; y - winding pitch along the grooves; a is the number of pairs of parallel branches in the phase; m is the number of phases; phase connection method - Y - star, L - triangle.
The stator windings are made single-layer and double-layer. The winding of single-layer windings is carried out mechanized on special machines.
Single-layer windings have a different shape, and the frontal parts of one coil group have the same shape, but different sizes (Fig. 2.25). To lay the winding in the grooves of the stator core, the frontal parts of the coils are arranged 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" of copper rods, the ends of which were soldered in holes drilled in copper short-circuited rings (see Fig. 2.3). In modern asynchronous electric machines with a power of up to 100 kW, the short-circuited winding of the rotor is formed by filling its grooves with molten aluminum.

С1 С6 С2 С4 СЗ С5
Rice. 2.25. (r \u003d 24; p \u003d 2): a - with an even number of pairs of poles; b - the location of the frontal parts; in - with an odd number of pairs of poles; g - the location of the frontal parts

In phase rotors of asynchronous motors, wave or loop windings are most often used. The most common wave windings, the advantage of which lies in the minimum number of intergroup connections. The main element of the wave winding is an ordinary rod. A two-layer wave winding is performed 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, which has 24 slots, is shown in fig. 2.26 a. The step 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 step equal to 6, it is necessary to connect the lower rod of the groove 19 with the upper rod of the groove 1, which means to close 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 groove are called windings with short transitions, and with an increased pitch by one groove - windings with elongated 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, the front pitch of the winding is distinguished from the side of the leads (slip rings) and the rear pitch of the winding from the side opposite to the slip rings. Bypassing the rotor in the opposite direction, in this case the transition to the back step, is achieved by connecting the lower rod of the groove 18 with the lower rod, which is one step behind it. Next, two bypasses of the rotor are made. Continuing to bypass the rotor in a backward step, the lower rod of the slot 12 is connected to the upper rod of the slot 6. Further connections do so. 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, and that, in turn, 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 phase rotors of asynchronous motors are connected mainly by a "star" with the output of the three ends of the winding to slip rings. The rotor winding leads are designated PI, P2, R3 (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 by 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, P3 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 (2m). When 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 are continued along the armature and collector until all grooves are filled and the winding closes.
Preparation of windings for repair. Repair of windings is carried out by specially trained workers at the winding sections of the repair department or enterprise. Preparation of machines for repair consists in the selection of winding wires, insulating, impregnating and auxiliary materials. The list of materials necessary for the repair of the windings is entered into the operational documentation of the electric machine.
To detect short circuits in the winding between turns of one coil or wires of different phases, special devices are used. Having determined the nature of the winding malfunction, they begin to repair it.
The technology of overhaul of the windings of electrical machines includes the following main operations:
winding disassembly;
cleaning the grooves of the core from the old insulation;
repair of the core and the mechanical part of the machine;
cleaning the winding coils from old insulation;
preparatory operations for the manufacture of the winding;
production of winding coils;
insulation of the core and winding holders;
laying the winding in the groove;
soldering winding connections;
fastening of the winding in the grooves;
drying and impregnation of the winding.
Repair of stator windings. The manufacture of the stator winding begins with the winding of individual coils on a template. To correctly select the size of the template, it is necessary to know the main dimensions of the coils, mainly their straight and frontal parts. The dimensions of the winding coils of the dismantled machines are determined by measuring the old winding.
Coils of loose stator windings are usually made on universal templates (Fig. 2.27). Such a template is a steel plate 1, which is connected to the spindle of the winding machine with the help of a sleeve 2 welded to it. The plate has the shape of a trapezoid. Four studs fixed with nuts are installed in its slot. When winding coils of different lengths, the pins are moved in the slots. When winding coils of different widths, the studs are moved 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 joints, all coils of one coil group are wound with solid 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 conductors of the coil can fit in them.

Rice. 2.27.: 1 - plate; 2 - bushing; 3 - hairpin; 4 - rollers

Sometimes, when repairing motor windings, it is necessary to replace the missing wires with wires of other brands and sections. For the same reasons, instead of winding the 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 the repaired engines, first (before winding the coils) they check the fill factor of the groove, which should be 0.7 - 0.75.
Coils of a two-layer winding are placed in the grooves of the core in groups, as they were wound on a template. The wires are distributed in one layer and put the sides of the coils that are adjacent to the groove. The other sides of the coils are not laid in the grooves until the lower sides of the coils are laid in all the grooves (Fig. 2.28). The next coils are placed simultaneously with the upper and lower sides. Between the upper and lower sides of the coils in the grooves, insulating gaskets are installed from electric cardboard bent in the form of a bracket, and between the frontal parts - from 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, take its real winding data (wire diameter, number of wires in the slot, winding pitch along the slots, etc.), and then make sketches of the front 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 cloth. Preliminarily, according to the dimensions of the grooves of the machine, a steel mandrel 1 is made, which consists of two oncoming 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 cloth are cut into a complete set of sleeves and they are made. The mandrel is heated to 80 - 100 ° C and tightly wrapped with a blank impregnated with varnish. A 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 they are filled with steel bars, the diameter of which should be 0.05 - 0.1 mm larger than the diameter of the insulated winding wire. A piece of wire is cut from the bay, which is necessary for winding one coil. A long wire complicates winding, and the insulation is often damaged due to its frequent pulling through the groove.
Winding into a broach is usually carried out by two winders that stand on both sides of the stator (Fig. 2.30). Front end insulation
windings of machines for voltages up to 660 V, intended for operation in a normal environment, are made with LES glass tape, with each next layer half-overlapping the previous one. Each coil of the group is wound, starting from the end of the core. First, the part of the insulating sleeve that protrudes from the groove is wrapped with tape, and then the part of the coil to the end of the bend. The middle of the heads of the group is wrapped with glass tape in full overlap. The end of the tape is fixed on the head with glue or sewn tightly to it. The winding wires that lie in the groove are held with the help of groove wedges made of beech, birch, plastic, textolite or getinaks. 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. For moisture resistance, wooden wedges are "boiled" 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 hammered 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 - slot insulation; 3 - extension
For the beginning of the phases, the conclusions of the coil groups are taken, which come out of the grooves located near the terminal board. These conclusions are bent to the stator housing and the coil groups of each phase are preliminarily connected, the ends of the wires of the coil groups stripped of insulation are twisted.
After assembling the winding circuit, the dielectric strength of the insulation between the phases and on the case is checked, 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 the 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. Such a check can also be carried out using a turntable. A hole is punched in the center of the tin disc, fixed with a nail at the end of a wooden plank, and then this spinner is placed in the bore of the stator, which is connected to the electrical network. If the circuit is assembled correctly, the disc will spin.
The correct assembly of the circuit and the absence of turn short circuits in the windings of the repaired machines are also checked by the El-1 electronic apparatus. Two identical windings or sections are connected to the device, and then, using a synchronous switch, voltage pulses are periodically applied to the cathode ray tube of the device. If there are no damages in the windings, the voltage curves on the screen are superimposed on one another, but if there are defects, they bifurcate. To detect the grooves in which short-circuited turns are located, a device with two U-shaped electromagnets for 100 and 2000 turns is used. The coil of the fixed electromagnet (100 turns) is connected to the terminals of the apparatus, and the coil of the movable electromagnet (2000 turns) is connected to the terminals "Sign. phenom.". In this case, the middle handle must be set to the leftmost 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 phase rotor, two main types of windings are used: coil and rod. The manufacture of loose and lingering coil windings of rotors is almost the same as the manufacture of the same stator windings.
In machines with a power of up to 100 kW, mainly rod two-layer wave windings of the rotors are used. In them, 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, therefore, after the restoration of the insulation, they are placed in the same grooves in which they were before the repair.
The assembly of the rod winding of the rotor 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 to the grooves with only one bent end. The other ends of these rods are bent with special keys after being laid in the grooves. First, the rods of the lower row are placed in the grooves, inserting them from the side opposite to the contact rings. Having laid the entire lower row of rods, their straight sections are placed on the bottom of the grooves, and the bent frontal parts are placed on an insulated winding holder. The ends of the bent frontal parts are strongly tightened with a temporary bandage made of soft steel wire, tightly pressing them to the winding holder. The second temporary wire bandage is wound around the middle of the frontal parts. Temporary bandages serve to prevent the rods from shifting during their 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 from the side opposite from the contact rings. Then put temporary bandages. The ends of the rods are connected with copper wire to check the absence of a short circuit to the body. If the test results are positive, continue assembling the winding, the ends of the upper rods are bent in the opposite direction. The bent frontal parts of the upper rods are also fixed with two temporary bandages.

Rice. 2.32. :
o - plate; b - "language"; c - reverse wedge; g - corner knife; d - drift; e - hatchet; ok, a - keys for bending the 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 oven. Then the insulation of the dried winding is tested.
The final operations for the manufacture of the rod winding of the rotor of the repaired machine are the connection of the rods, the driving of the wedges into the grooves and the banding of the winding. To increase the reliability of machines, the connection of rods by hard soldering is used.
The windings of the phase rotors of asynchronous motors are connected mainly by a "star".

Most asynchronous motors up to 100 kW are manufactured with a squirrel-cage rotor, which is made of aluminum by casting.
Repair of a cast rotor with a damaged rod consists of recasting it after aluminum smelting and cleaning the grooves. For this purpose, chill molds are used.
In large electrical repair plants, squirrel-cage rotors are poured with aluminum in a centrifugal or vibration method, and injection molding is also used.
Repair of anchor windings. The main malfunctions of the armature windings: the connection of the winding to the body, interturn short circuits, breaks in the windings, mechanical damage to solder joints.
When preparing the armature for repair, they remove the old bandages, solder the connections to the collector, remove the old winding, having previously recorded all the data necessary for the repair.
In DC machines, rod and template windings of armatures are used. The rod windings of the armatures are performed in the same way as the rod windings of the rotors.
For winding sections of the template winding, insulated wires are used, as well as copper tires, which are insulated with varnished cloth or mycol tape. Template winding sections are wound on universal templates, which allow winding and then stretching of a small section without removing it from the template. The stretching of sections of anchors of large machines is performed on special machines with a machine drive. Before stretching, the section is secured by temporarily wrapping it with a single layer of cotton tape to ensure that the section is formed correctly when stretched.
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 that are turned towards the collector, as well as the distances from the edge of the core to the transition of the straight (groove) part to the frontal 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 the soldering is checked by external inspection, by measuring the contact resistance between adjacent plates, by passing the working current through the armature winding. With high-quality soldering, the transition resistance between all pairs of plates should be the same. When passing through the armature winding for 20 - 30 minutes of rated current, local heating should not occur.

Repair of pole coils.

Most often, the coils of additional poles, which are wound with a rectangular copper bus with a plaza or on an edge, turn out to be damaged. Usually the insulation between the turns of the coil is damaged. When repairing, 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 pulled together with a cotton tape and pressed. To do this, put an end insulating washer on the mandrel, put a coil on it and cover it with a second washer. Then the coil is compressed on the mandrel, attached to the 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 - to isolate the wound coil; 1, 4 - micanite and cotton ribbons; 2 - template; 3 - copper bus;
5-pole coil
The outer surface of the coil is insulated with asbestos and then with micanite tape and varnished. The finished coil is put on an additional pole and fastened 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 are 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 power and retain their insulating properties for a long time.
The windings of electrical machines are impregnated one, two or three times, depending on the operating conditions and the requirements for them. During the impregnation process, the viscosity and thickness of the lacquer must be constantly checked, as the solvents evaporate and the lacquer 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.
The windings of electrical machines after impregnation are dried in special chambers with natural or forced ventilation with thermal air. Heating can be electric, gas, steam. The most common drying chambers are electrically heated.
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. In the subsequent hours of drying, part of the exhausted warm air, containing a small amount of moisture and solvent vapors, returns to the chamber. The maximum temperature in the chamber does not exceed 200°C.
During the 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 by 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 raise the temperature above 100 - 110 ° C, since a varnish film may form prematurely.
In the process of baking the lacquer film, it is possible to increase the drying temperature of windings with class A insulation for a short time (no more than 5–6 hours) up to 130–140 °C.
At large electrical repair enterprises, impregnation and drying are carried out on special impregnation-drying conveyor installations.
After repair, electrical machines are sent for testing.

1. What methods of winding coils with tapes are used when insulating them?
2. How are insulating materials classified according to 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 wrapping pattern work?
7. How is the template winding laid in the grooves?
8. How is the rod winding made?
9. What devices are used when making armature coils?
10. How is the end windings insulated?
11. What malfunctions can occur in pole coils?
12. Why are windings dried?
13. Winding impregnation process.

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