Winding repair electric 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 requirements for electrical and mechanical strength, heat resistance, and moisture resistance.
Preparing machines for repair consists of selecting winding wires, insulating, impregnating and auxiliary materials.
Technology overhaul windings of electrical machines includes the following basic operations:
winding disassembly;
cleaning the core grooves from old insulation;
repair of the core and mechanical part of the machine;
cleaning the winding coils from old insulation;
preparatory operations for the manufacture of windings;
production of winding coils;
insulation of the core and winding holders;
laying the winding in the groove;
soldering winding connections;
fastening the winding in the grooves;
drying and impregnation of the winding.
Repair of stator windings. The manufacture of the stator winding begins with winding individual coils on a template. To choose the right template size, you need to know the main dimensions of the coils, mainly their straight and frontal parts. The dimensions of the winding coils of dismantled machines are determined by measuring the old winding.
Coils of stator random windings are usually made on universal templates (Fig. 5).
This template is steel plate 1, which using
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 -- bushing; 3 -- hairpin; 4 -- rollers
Its slot contains four studs secured with nuts. When winding coils of different lengths, the pins are moved in the slots. When winding coils of different widths, the pins are rearranged from one slot to another.
In the stator windings of AC machines, usually several adjacent coils are connected in series and they form a coil group. To avoid unnecessary solder connections, all coils of one coil group are wound with a single wire. Therefore, rollers 4, machined from textolite or aluminum, are put on the studs 3. The number of grooves on the roller is equal to the largest number of coils in the coil group; the dimensions of the grooves must be such that all the coil conductors can fit into them.
The coils of a two-layer winding are placed in the grooves of the core in groups, as they were wound on the template. The wires are distributed in one layer and the sides of the coils are placed, which are adjacent to the groove. The other sides of the coils are not placed in the grooves until the bottom sides of the coils are placed in all the grooves. The following coils are placed with their upper and lower sides simultaneously.
Between the upper and lower sides of the coils, insulating gaskets made of electrical cardboard, bent in the form of brackets, are installed in the grooves, and between the frontal parts - made of varnished fabric or sheets of cardboard with pieces of varnished fabric glued to them.
The manufacture of windings with closed slots has a number of features. The groove insulation of such windings is made in the form of sleeves made of electrical cardboard and varnished fabric. A steel mandrel, which consists of two opposing wedges, is first made according to the dimensions of the machine’s grooves. The mandrel should be smaller than the groove by the thickness of the sleeve. Then, according to the size of the old sleeve, blanks from electric cardboard and varnished fabric are cut into a complete set of sleeves and they begin to manufacture them. Heat the mandrel to 80 - 100 °C and tightly wrap it with a workpiece impregnated with varnish. Cotton tape is tightly laid on top of the workpiece with a full overlap. After the mandrel has cooled to ambient temperature, the wedges are spread and the finished sleeve is removed. Before winding, the sleeves are placed in the grooves of the stator, and then filled with steel rods, the diameter of which should be 0.05 - 0.1 mm larger than the diameter of the insulated winding wire. A piece of wire needed to wind one coil is cut from the coil. A long wire complicates winding, and the insulation is often damaged due to frequent pulling it through the groove.
Insulation of the frontal parts of the windings of machines with voltages up to 660 V, intended for operation in a normal environment, is carried out with LES glass tape, with each subsequent layer semi-overlapping the previous one. Each coil of the group is wound starting from the end of the core. First, tape the part of the insulating sleeve that protrudes from the groove, and then the part of the coil to the end of the bend. The middles of the group heads are completely overlapped with glass tape. The end of the tape is fixed to the head with glue or tightly sewn to it. The winding wires, which lie in the groove, are held using groove wedges made of beech, birch, plastic, textolite or getinax. The wedge should be 10 - 15 mm longer than the core and 2 - 3 mm shorter than the groove insulation and at least 2 mm thick. For moisture resistance, wooden wedges are “cooked” for 3–4 hours in drying oil at 120–140 °C.
The wedges are driven into the grooves of medium and small machines with a hammer and using a wooden extension, and into the grooves of large machines with a pneumatic hammer. Then the winding circuit is assembled. If the winding phase is wound with separate coils, they are connected in series into coil groups.
The beginning of the phases is taken to be the conclusions of the coil groups, which come out of the grooves located near the output panel. These leads are bent to the stator housing and the coil groups of each phase are pre-connected, and the ends of the wires of the coil groups, stripped of insulation, are twisted.
After assembling the winding circuit, check the electrical strength of the insulation between the phases and on the housing, as well as the correctness of its connection. To do this, use the simplest method - briefly connect the stator to the network (127 or 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. This check can also be carried out using a pinwheel. A hole is punched in the center of the tin disk, secured with a nail at the end of a wooden plank, and then this pinwheel is placed in the stator bore, which is connected to the electrical network. If the circuit is assembled correctly, the disk will rotate.
Banding of rotors and anchors
When the rotors and armatures of electric machines rotate, centrifugal forces arise, tending to push the winding out of the grooves and bend its frontal parts. To counteract centrifugal forces and hold the winding in the grooves, wedging and banding of the rotor and armature windings are used.
The method of fastening the windings (with wedges or bands) depends on the shape of the rotor or armature slots. When the grooves are open, bandages or wedges are used. The grooved parts of the windings in the cores of armatures and rotors are secured using wedges or bandages made of steel bandage wire or glass tape, as well as simultaneously with wedges and bandages; the frontal parts of the windings of rotors and armatures are covered with bandages. Reliable fastening of the windings is important, since it is necessary to counteract not only centrifugal forces, but also the dynamic forces to which the windings are exposed during rare changes in the current in them. To bandage the rotors, tinned steel wire with a diameter of 0.8 - 2 mm, which has a high tensile strength, is used.
Before winding the bands, the frontal parts of the winding are hammered through a wooden spacer so that they are evenly positioned around the circumference. When banding the rotor, the space under the bands is first covered with strips of electrical cardboard to create an insulating spacer between the rotor core and the band, protruding 1-2 mm on both sides of the band. The entire bandage is wound with one piece of wire, without soldering. On the frontal parts of the winding, in order to prevent their swelling, turns of wire are placed from the middle of the rotor to its ends. If the rotor has special grooves, the wires of the bandages and locks should not protrude above the grooves, and if there are no grooves, the thickness and location of the bands should be the same as they were before the repair. The brackets installed on the rotor should be placed over the teeth, not over the slots, and the width of each should be less than the width of the top of the tooth. The brackets on the bands are placed evenly around the circumference of the rotors with a distance between them of no more than 160 mm. The distance between two adjacent bands should be 200-260 mm. The beginning and end of the bandage wire are sealed with two locking brackets 10-15 mm wide, which are installed at a distance of 10-30 mm from one another. The edges of the staples are wrapped around the turns of the bandage and... soldered with POS 40 solder.
To increase strength and prevent their destruction by centrifugal forces created by the mass of the winding during rotation of the rotor, fully wound bandages are soldered over the entire surface with POS 30 or POS 40 solder. Soldering of bandages is carried out with an electric arc soldering iron with a copper rod with a diameter of 30 - 50 mm, connected to a welding transformer . In repair practice, wire bands are often replaced with glass tapes made of unidirectional (in the longitudinal direction) glass fiber impregnated with thermosetting varnishes. For winding glass tape bandages, the same equipment is used as for bandaging with steel wire, but supplemented with devices. in the form of tension rollers and tape stackers.
In contrast to banding with steel wire, the rotor is heated to 100 °C before wrapping glass tape bands around it. Such heating is necessary because when a bandage is applied to a cold rotor, the residual stress in the bandage during baking decreases more than when bandaging a heated one. The cross-section of a fiberglass bandage must be at least 2 times larger than the cross-section of the corresponding wire bandage. The last turn of glass tape is attached to the underlying layer during the process of drying the winding during sintering of the thermosetting varnish with which the glass tape is impregnated. When banding the rotor windings with glass tape, locks, brackets and under-band 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 complete with fans and other rotating parts. Balancing is carried out on special machines to identify imbalance (imbalance) of the masses of the rotor or armature, which is common cause occurrence 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 different thicknesses or masses of individual parts, the presence of shells in them, uneven projection 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, the 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.
Imbalance, 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 of 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 existing equipment. With dynamic balancing, better results of imbalance compensation are obtained (less residual imbalance) than with static balancing.
To determine imbalance, the rotor is brought out of balance with a slight push. An unbalanced rotor (armature) will tend to return to a position in which its heavy side is down. After the rotor stops, mark with chalk the place that is in the upper position. The technique 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.
Test weights are installed in the space reserved for balancing weights (most often this is the inner diameter of the rim of the pressure washer), attaching them with putty. After this, repeat the balancing technique. By adding or decreasing the mass of weights, the rotor is stopped in any arbitrary position. This means that the rotor is statically balanced, that is, its center of gravity is aligned with the axis of rotation. Upon completion of balancing, the test weights are replaced with one of the same cross-section and mass, equal mass test weights and putty and a part of the electrode reduced by weight, which will be used for welding the permanent weight. Unbalance can be compensated for by drilling out a suitable piece of metal from the heavy side of the rotor.
Balancing on special scales is more accurate than with prisms and disks. The rotor to be balanced is mounted with the journals of the shaft on the supports of the frame, which can rotate around its axis at a certain angle. By rotating the rotor to be balanced, the maximum reading of the indicator J is achieved, which will be provided that the center of gravity of the rotor is located.
By adding additional weight to the load - frames with divisions - the rotor is balanced, which is determined by the indicator arrow. At the moment of balancing, the arrow aligns with the zero division.
If you rotate the rotor 180, its center of gravity will approach the frame swing axis by double the eccentricity of the displacement of the rotor center of gravity relative to its axis. This moment is judged by the lowest indicator reading. The rotor is balanced a second time by moving the load frame along a ruler with a scale graduated in grams per centimeter. The magnitude of imbalance is judged by the readings of the scale.
Static balancing is used for rotors rotating at a speed not exceeding 1000 rpm. A statically balanced rotor (armature) may have dynamic imbalance, therefore rotors rotating at a frequency above 1000 rpm are most often subjected to dynamic balancing, in which both types of imbalance - static and dynamic - are simultaneously eliminated.
Having secured a permanent load, the rotor is subjected to test balancing and, if the results are satisfactory, it is transferred to the assembly department for assembly of the machine.
Assembly and testing of electrical machines Assembly is the final stage of repair of an electrical machine, during which the rotor is connected to the stator using bearing shields with bearings and the remaining parts of the machine are assembled. As a rule, the assembly of any machine is carried out in the reverse order of disassembly.
The machine is assembled 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 performing the main assembly
Machine assembly direct current P-41 (Fig. 6) is produced as follows. Place 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 secure them with bolts. They check the distance between the pole pieces with a template, and the distance between opposite poles with a stichmas.
Figure 6 - DC machine P-41
Put the coils on the additional poles 13, insert the poles with the coils into the frame 16 according to the markings made during disassembly, and fasten them with bolts. They check the distances between the pole pieces of the main and additional poles with a template, and the distances between opposite additional poles with a pin. The coils of the main and additional poles are connected according to the connection diagram. Check the polarity of the main and additional poles, as well as the amount of overhang of the winding 12 located in the armature core 14. Place the fan on shaft 7 according to the marks made during disassembly. Place grease in the labyrinth grooves. Place the inner covers of 2 and 20 bearings on the shaft. Heat the ball bearings in an oil bath or by induction and place them on the shaft using a device. Place grease in the bearings. Insert the anchor into the frame using a device. Assemble the traverse 6 together with the brush holders on the device and grind the brushes. Screw the traverse with brush holders to the bearing shield 5 and lift the brushes from the sockets of the brush holders. Slide the rear bearing shield 18 onto the ball bearing, lift the armature by the end of the shaft and slide the bearing shield onto the frame lock. Screw the bearing shield bolts into the holes at the end of the frame without tightening them to capacity. Slide the front bearing shield 5 onto the ball bearing 3. Raise the armature and insert the bearing shield into the frame lock. Screw the bearing shield bolts into the holes at the end of the frame without tightening them to capacity. Check the ease of rotation of the armature by gradually tightening the bolts of the bearing shields. Place the ball bearing cover 4 and tighten the covers with 4 and 2 bolts. Place grease into the labyrinth grooves. Place the ball bearing cover 19 and secure the covers with 19 and 20 bolts. Check the ease of rotation of the armature by rotating it by the end of the shaft. Lower the brushes onto the commutator. Check the distances between the brushes of different fingers along the circumference of the commutator and the shift of the brushes along the length of the commutator. Check the distances between the commutator and the brush holders. Clamps 7 are assembled on a board 9 in a box 8 and capacitors 10 are attached to it. The assembled clamp board is installed on the front bearing shield 5. Produce electrical connections according to the diagram. Check the distance between the armature and the poles with probes. Connect the mains power wires to the terminals. Carry out a test run of the car. During the running-in process, the operation of the brushes and bearings is checked. Brushes should work without sparking, bearings - without noise. After finishing the run-in, close the manifold hatches with covers. Disconnect the power wires and close the terminal box with a lid. They hand over the assembled car to a foreman or quality control inspector.
When performing assembly work, the electrician must remember that the rotor of the electric motor, held in the central position by the magnetic field of the stator, must be able to move (“run up”) in the axial direction. This is necessary so that the rotor shaft, at the slightest displacement, does not wear out the ends of the bearings with its sharpening and does not cause additional forces or friction of the mating parts of the machine. The axial take-off values, depending on the power of the machine, should be: 2.5 - 4 mm at a power of 10-40 kW and 4.5 - 6 mm at a power of 50-100 kW.
After repair, all machines are checked for heating of the bearings and the absence of extraneous noise. For machines with a power above 50 kW at a rotation speed of more than 1000 rpm and for all machines with a rotation speed above 2000 rpm, the vibration value is measured.
The gaps between the active steel of the rotor and stator, measured at four points around the circumference, must be the same. The dimensions of the gaps at diametrically opposite points of the rotor and stator of an asynchronous electric motor, as well as between the centers of the main poles and the armature of a DC machine, should not differ by more than ±10%.
Electrical machine testing. In repair practice, the following types of tests are encountered mainly: before the start of repairs and during the repair process to clarify the nature of the malfunction; newly manufactured machine parts; assembled after the car was repaired.
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 correct marking of the output ends;
measurement of winding resistance to direct current;
checking the transformation ratio of asynchronous motors with a wound rotor;
conducting an idle test; high speed test; turn-to-turn insulation test; electrical insulation strength test.
Depending on the nature and scope of the repairs performed, sometimes they are limited to performing only 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 control testing program for 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 housing and between the phases of the windings;
3) measurement of the ohmic resistance of the winding in a cold state;
4) determination of the transformation ratio (in machines with a wound rotor);
5) testing the machine at idle speed;
6) measurement of no-load currents by phase;
7) measurement of starting currents in squirrel-cage motors and determination of the starting current multiplicity;
8) testing the electrical strength of turn insulation;
9) testing the electrical strength of insulation relative to the housing and between phases;
10) conducting a short circuit experiment;
11) heating test when the engine is running under load.
The program of control tests of 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;
measuring the insulation resistance of the windings relative to the housing;
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 additional poles with
checking the consistency of the polarities of the coils of serial and parallel excitations;
checking the alternation of polarities of the main and additional poles;
testing the machine at idle speed;
testing the electrical strength of turn insulation;
testing the electrical strength of insulation relative to the housing;
heating test when the machine is running under load.
Operating conditions of electrical machines. Conditions in which electric machines operate. p.s., and first of all, traction engines are very heavy. Unlike permanently installed machines, they are subject to environmental influences, dynamic shocks from the rail track, and operate under conditions of widely and sometimes sharply changing current and voltage values.
Despite the measures taken, moisture and dust get into cars from the environment. Moisture penetrates into the pores of the insulation of machine windings, which leads to a decrease in its electrical strength, creates conditions for the occurrence of electrical or thermal breakdown, and leads to accelerated aging. In combination with low temperatures moisture contributes to the appearance of frost and icing of the commutator and brush apparatus, which leads to increased sparking under the brushes. Increased sparking also occurs from contamination of the collector and brush apparatus with dust entering the machine through leaks in the hatches and with the cooling air.
Ambient temperatures can reach - 40 °C in winter and up to + 50 °C in summer. Heat worsens the cooling of electrical machines, contributes to their excessive heating, and low temperatures cause thickening of the lubricant in the bearings, sweating of the machines when installing electrical power. p.s. at the depot.
When passing uneven paths, the wheel pairs e. p.s. perceive significant dynamic forces (especially at high speeds). These shocks, partially smoothed by the spring suspension system, are transmitted to the traction motors. They are most sensitive for traction engines with axial support, almost half of the mass of which is not sprung.
The action of dynamic forces can cause cracks, fractures, increased wear of rubbing surfaces in machine elements, increased sparking on the commutator, and weakened joints.
The voltage in the contact wire, and therefore the voltage supplied to the traction motors (and other electrical machines), may differ from the nominal value (/nom by 10-12%. In some cases (for example, during regenerative braking) the voltage at the terminals of the traction motors can reach up to 1.25 bt - The voltage on the traction motors associated with boxing wheel pairs increases noticeably.When the pantograph is separated from the contact wire, the voltage on the traction motors sharply decreases, and during lightning discharges, it sharply increases.
Any voltage deviation from the nominal value impairs the operation of the traction motor and reduces its traction properties. But especially dangerous is increased voltage, which can cause potential sparking on the commutator and the formation of a circular fire, breakdown of the insulation of windings, wires, insulation of brush holder brackets, and output cables.
When starting or moving along a long ascent of heavy trains or when moving with an incomplete number of traction motors operating on the locomotive, the currents in them can significantly exceed their permissible values. Such even short-term overloads can cause increased sparking under the brushes, disrupt commutation, and, under certain conditions, lead to the formation of a circular fire on the commutator.
A circular fire can also arise as a result of a rapid increase in current during transient processes occurring in traction motors. The most dangerous are transient modes that arise as a result of the formation of a circular fire on an adjacent parallel-connected engine or when a rectifier arm breaks down. No less dangerous are modes of shock switching on full voltage to a previously de-energized traction motor, for example, when reapplying voltage to the motor at a time when the main handle of the driver’s controller is not returned to the zero position.
The operation of electrical machines with currents exceeding the permissible values also leads to their excessive heating, which accelerates the aging of the insulation and limits the full use of their power.
When the wheelset slips, the rotation speed of the traction motor armature increases sharply. In this case, large centrifugal forces arise, which can cause damage to the shafts of the traction motor anchors, elastic couplings, fans, and weakening or damage to the anchor bands. In addition, with an increased frequency of rotation of the armature, sparking under the brushes noticeably increases, the switching of the machine deteriorates and conditions are created for the possible occurrence of an all-round fire on the commutator. At the moment the traction of the boxing wheelset is restored, the speed of its rotation (and, consequently, the associated engine armature) instantly decreases. In this case, the reserve of kinetic energy of the rotating armature turns into a shock transmitted to the gear train, armature shaft, bearings and other engine elements, causing their increased wear and sometimes breakdown.
Statistics have established that about 30-40% of cases of electrical failures. p.s. in operation is associated with malfunctions that occur in electrical machines. In order to increase their reliability, the Rules for the repair of traction engines and auxiliary machines of electric rolling stock TsT 2931 (hereinafter referred to as the Repair Rules) provide for appropriate preventive measures and establish a specific procedure and timing for their implementation.
Thus, the Repair Rules provide for the repair of traction engines and auxiliary machines of three types: depot, factory volume I (medium) and factory volume II (major), and also establish the frequency of their implementation. At the same time, the possibility of deviation from the established network-wide overhaul runs by 20% in both directions is discussed in order to make it easier for factories and depots to plan repairs more evenly throughout the year. The Main Directorate of Locomotive Facilities of the Ministry of Railways has been given the right to change repair periods for certain types of electrical machines.
When repairing electrical machines, replacement of their main components is not allowed, therefore bearing shields, axle boxes of motor-axial bearings, anchor bearings, traverses and other parts are marked. It is advisable to install the anchor in its own frame. These requirements are mandatory, as they ensure the maximum reduction in labor costs while maintaining the necessary characteristics and parameters of the electrical machine after assembly.
Before installation on the machine, all repaired or new parts are checked, tested and presented for acceptance to the foreman or locomotive acceptor.
Each electrical machine released from repair is subjected to control tests in accordance with state standards and the requirements of the Rules for the repair of traction and auxiliary electrical machines. p.s.
Preliminary preparation of machines for disassembly. After disassembling the wheel-motor unit, the gears are pressed from the shaft of the traction motor of the electric locomotive, and the flange of the elastic coupling is pressed from the shaft of the traction motor of the electric train, using mechanical, pneumatic or oil pullers.
Rice. 3.1. Preparing the motor shaft for gear removal
The least possible damage to the seating surfaces of the gear, coupling half and shaft is ensured by oil pullers. However, their use requires preliminary special preparation of the shafts (Fig. 3.1). On the shaft journal 4 in the middle, the seating surface, a circular open groove 3 is made, its ends slightly not reaching the keyway 2. The center hole of the shaft is connected to groove 3 by channel 5. Through the center hole, oil is pumped into groove 3 with an oil pump, the fit of gear 1 is significantly tight decreases and is easily removed from the shaft.
Then remove the caps of the motor-axial bearings, remove the bearing shells and padding, and remove any remaining oil from the inner surfaces of the bearings with a rag soaked in gasoline.
Rice. 3.2. A two-chamber machine for external washing and drying of traction motors before disassembling the catch and caps and installing the caps in their original places (but without liners and padding).
Taken from e. p.s. Electrical machines and, first of all, traction motors are usually heavily contaminated (up to 15-20 kg of various waste is removed from the engine during cleaning, including about 10-12 kg of grease and oil from motor-armature and motor-axial bearings). Such contamination makes it difficult to identify defects during inspection and leads to a decrease in the quality of subsequent repairs.
The traction motor is cleaned before installing it at the first position of the disassembly production line.
The outside of the engine is first cleaned manually using scrapers and rags. For final cleaning, the engine is washed in special washing machines (one- or two-chamber).
A two-chamber washing machine (Fig. 3.2) consists of two hermetically sealed chambers. In chamber 1, the engine is washed with hot (80-90 °C) water 9, which is supplied by pump 1 to a rotating shower device 2 from drive 5. To prevent moisture from getting inside the engine, all ventilation and other openings in the frame are carefully closed with special plugs and covers, and in place of the upper manifold hatch cover, a special pipe 3 is attached, through which air is supplied to the engine from the fan 4, creating excess pressure inside it. After washing, the intermediate door 8 is raised and the engine is moved on a self-propelled cart into the chamber //, where closed door 7 dry it for 15-20 minutes with a stream of air heated from heater 6.
The rotation speed of the shower and drying devices is 2 rpm. Both cameras can work simultaneously.
The cleaned machine is installed at position 1 of the repair production line (Fig. 3.3), where it is carefully inspected.
Inspection to identify external defects is carried out visually. At the same time, the hull numbers are checked,
Rice. 3.3. Traction motor repair production line:
1 - disassembly line; II - impregnation department; III - assembly line; IV - anchor repair line; 1, 17 - defective positions; 2- disassembly position; 3- blowing chamber; 4- tilter; 5- position of repair of the mechanical part; 6, 23 - transport trolley; 7- welding station; 8- position for checking the electrical strength of insulation; 9 – assembly position; 10 - installation position of brush holders; II - engine assembly position; 12- stand for testing the engine at idle speed; 13- testing station; 14- engine anchor; 15 - purge chamber; 16- tilter; 18- balancing machine; 19- machine for soldering manifold cockerels; 20, 22, 26, 28 - drives; 21, 27 - positions, respectively, for repairing and checking the electrical part of the armature; 24, 25 - machines for grinding and groove of bearing shield collectors and caps of motor-axial bearings.
Then measure electrical parameters machines, determine the axial run-up of the armature, runout and wear of the commutator, radial clearances of the armature bearings and runout of the outer rings.
To perform the above measurements, repair position 1 is equipped with the necessary measuring instruments, a static converter with a terminal column and an induction heater for removing inner rings of bearings and labyrinth rings.
The insulation resistance of traction motors is measured with a 2.5 kV megohmmeter. (To eliminate additional errors, the insulation resistance should be measured with megohmmeters for the appropriate voltage.)
When measuring insulation resistance, connect the beginning (or end) of the circuit of the main poles to the beginning (or end) of another circuit - additional poles and the armature winding. The “L” clamp of the megohmmeter is connected to these terminals. Its second clamp “3” is connected to the machine body. During the measurement process, it is necessary to ensure that the lead ends of the controlled windings do not touch the floor or the motor housing, otherwise the instrument readings will be incorrect. For serviceable traction motors, the insulation resistance must be at least 5 MOhm. If it turns out to be less, you should measure the resistance of individual circuits (main and additional poles, armature windings) and identify the damaged area, keeping in mind that the decrease in resistance could be caused by moisture or malfunction of the brackets and inter-coil connections.
The insulation resistance is measured before washing the engine.
The insulation resistance of auxiliary machines must be at least 3 MOhm. Methods for checking and identifying defective places in insulation for auxiliary
5 is. 3.4. Installation of an indicator for measuring collector voltage
Rice. 3.5. Device for measuring commutator runout
Rice. 3.6. Measuring the output of the collector with a template of driving machines is the same as for traction engines.
The active resistance of the windings of electrical machines is usually measured with an MDb (or UM13) bridge and compared with the value set for a machine of this type. An increase in active resistance can be caused by defects in pole coils, melting of cables in cartridges or lugs, broken wires of output cables or intercoil connections and poor contact in these connections.
To identify the cause of the increase in resistance, the suspected winding of the machine is connected to a static converter and a current equal to twice the value of its clock current is installed in it. The defective area is detected by touch by increased heating.
Then, when the engine rotates under a voltage of 220-400 V without load, the operation of the armature bearings, engine vibration, commutator beating and the operation of the brush apparatus are checked.
Anchor bearings are checked by their heating and by ear when the engine armature rotates at a frequency of about 700-750 rpm for 5-10 minutes in each direction. A serviceable bearing should operate without cracking, clicking, or jamming, and when the machine is idling, it should not overheat relative to the ambient temperature by more than 10 °C.
Engine vibration is also checked when it is idling at a speed of 700 rpm. Vibration is measured using a hand-held vibrograph VR-1. The location where the vibrograph is applied to the engine body can be anywhere. If the engine vibration is more than 0.15 mm, the armature must be balanced.
The runout of the collector is measured by indicator 1 (Fig. 3.4), which is brought to the collector 4 through the collector hatch and secured with a clamp 2 on the edge of the frame 3. The runout is measured along the middle part of the working length of the collector and at a distance of 10-20 mm from its outer cut. If it exceeds the maximum permissible value, then the collector must be turned.
The commutator runout can also be measured using a device (Fig. 3.5), the body 1 of which is fixed to the brush holder bracket. By moving slider 2 to working part collector, set indicator 3 to zero and, when rotating the collector, determine the runout.
The wear and tear of the working part of the collector can also be measured using this device. To do this, the slider is first moved to the non-working part of the collector, the indicator is set to zero, and then, with the collector stationary, the slider is moved along the entire working part of the collector and fixed to the indicator highest value production.
In the absence of the described device, production can be measured with a template or a probe and a ruler.
The template (Fig. 3;6) is installed on the collector 2 and held by hand so that the block 1 of the device is located strictly parallel to the collector plates, and its end coincides with the end of the collector. By rotating the micrometer heads 3 alternately, the production is determined at two points along the length of the collector.
To determine production with a probe and a ruler (Fig. 3.7), ruler 2 is installed with a narrow edge on the collector plate 3 and with probe 1, along its entire length, the gap is measured between the lower edge of the ruler and the working surface of the plate. Such measurements are made in several places around the circumference of the collector.
The switching of the machine is assessed by the degree of sparking* under the brushes. If, during a visual assessment, the sparking under the brushes turns out to be more than a g/g point (see p. 156), and no defects are identified in the brush-collector assembly, then a thorough check of the magnetic system of the machine, its individual components and switching adjustment are necessary.
The radial clearances of the armature bearings are checked with plate feeler gauges on a stationary machine. To do this, remove the outer covers and labyrinth rings of the shield bearings and check the gap between the roller and the inner ring of the bearing in its lower part with a feeler gauge. For most types of traction motors it should be in the range of 0.09-0.22 mm.
Rice. 3.7. Determining collector depletion using a ruler and feeler gauge
Runout of the outer rings of bearings is a consequence of their distortions when installed on engines. Such misalignments lead to a significant increase in stresses at the edge of the raceway, increased wear and damage to the cages, radial or axial pinching of the rollers, and sometimes to destruction of the bearings.
You can detect ring misalignment using a special device developed by VNIIZhT. The device (Fig. 3.8) has a ring 4, which is put on the motor shaft 5 until it stops in the inner ring of the bearing and is secured to it with three centering screws 6. A stand 2 with an indicator 3 is fixed to the ring. The indicator rod 3 must rest its end against the outer ring bearing 1.
To measure vertical misalignment, the device is mounted on the shaft and mounted
Rice. 3.8. Installation for measuring misalignment of anchor bearings
Pour the indicator in the upper position to zero. Then the indicator is rotated 180° relative to the shaft and the end runout is determined (taking into account the sign of the arrow deflection). In the same way, runout is determined in the horizontal plane. The runout value is determined as the maximum difference in the indicator readings. For a correctly installed bearing, the runout of the outer ring end should not exceed 0.12 mm.
The axial run of the anchor is measured with an indicator. To do this, the anchor is moved as far as it will go in one direction, and on the opposite side, an indicator is fixed on a special stand and pressed against the end of the armature shaft or box (on ChS2 electric locomotive engines) so that the head arrow is at zero. Then the anchor is moved all the way to the other extreme position. The deviation of the indicator arrow will indicate the axial run. For traction motors with direct and helical gears it should be, respectively, no more than 0.2-0.8 and 5.9-8.4 mm, for auxiliary machines - 0.6-0.15 mm.
The air gaps between the pole cores and the machine armature are checked with probes. The gaps should not exceed the values established by the Repair Rules for machines of this type.
Otherwise, the magnetic symmetry of the machine will be broken, its characteristics will change, and switching stability will decrease. Inadmissible deviations in the values of air gaps must be eliminated when repairing the machine, and when testing it, careful debugging of the switching must be carried out.
The results of the inspection of electrical machines and the measurements taken are entered into a special journal for later use in determining the required scope of their repair, after which the engine is transferred to its disassembly position 2 (see Fig. 3.3).
Dismantling of electrical machines. Electrical machines are dismantled on conveyor lines, and in their absence, at specialized workplaces equipped with the appropriate equipment and tools.
Traction motors of domestic electric locomotives are dismantled in a vertical position. Using a hoisting-and-transport trolley (or crane), the engine is installed on the disassembly stand with the manifold down.
When performing any operations related to turning the engine from a horizontal to a vertical position, it should be remembered that in this case the anchor bearing receives the impact from the armature and is loaded with its full weight, and all this load is perceived mainly by the shoulders of the bearing rings and the ends of the rollers. These forces can be especially large when there are significant axial runs of the anchor in the frame. Therefore, any operation of turning electric motors to avoid damage to the bearings should be performed without jerking and with extreme caution.
The collector hatch covers and ventilation grids are removed from the engine, the supply cables are disconnected from the brush holder brackets, the labyrinth seals, rings, bearing shield covers are removed and the brushes are removed from the brush holders. The labyrinth rings are removed while hot using an electromagnetic puller. After removing the labyrinth rings, the bearing shield covers are installed in their places. Use a ratchet wrench to unscrew the bolt of the brush holder traverse clamp, rotate the clamp 180°, loosen the bolts of the locking device by three or four turns, and compress the traverse through the lower inspection hatch, leaving a gap of no more than 2 mm at the cut site.
Using a pneumatic impact wrench, unscrew the bearing shield mounting bolts on the side opposite to the commutator, press out the bearing shield using a hydraulic press and transport it to a press for pressing out the armature bearings or install it in a special shipping cassette. When pressing out the shields, do not allow them to become distorted in the neck of the frame, as this can lead to damage to the seating surfaces.
An eye is screwed onto the armature shaft (or screwed in if the shaft has an internal thread under the eye), hooked to it with a crane hook, smoothly and strictly vertically, so as not to damage the collector and bearing, the anchor is removed from the frame and transported to the storage unit of the anchor repair production line.
Labyrinth and thrust bushings, as well as inner rings anchor bearings are left on the armature shaft and pressed off it only when it is necessary to repair or replace them.
Then the engine frame is turned 180°, the second bearing shield is pressed out, the brush holders and brackets are removed, or the traverse along with the brush holders is removed from the frame using a special grip and crane.
To press out the outer rings of the anchor bearings, a steel ring 5 is installed between the support plate 1 (Fig. 3. 9) and the bearing shield 2, the height of which is slightly greater than the height of the bearing ring, and the inner diameter is 3-4 mm greater than its outer diameter. The press force P is transmitted to the bearing ring 4 through a steel disk 3, ensuring uniform distribution of force around the circumference of the bearing ring.
It is possible to remove the cardan shaft from the armature of the AB-4846eT engine of the ChS2 electric locomotive only after freeing the anchor box chamber from lubricant. Therefore, these engines are disassembled in a horizontal position. First, the collector hatch covers and ventilation grids are removed from them, the current-carrying wires are disconnected and the brushes are removed from the brush holders. Then the bearing shields are pressed out, the traverse is removed, the oil chamber of the anchor box is opened, the oil is drained from it, the propeller shaft with the coupling is removed, and only after that, using a special device - mounting bracket 3 (Fig. 3.10)
Rice. H.9.. Pressing out the bearing shield from the frame of the traction motor, remove armature 2 from the frame 1 of the traction motor.
Traction motors of electric trains are also dismantled in a horizontal position.
Bearing shields, covers, sealing rings, traverses with brush holders, and axle boxes of motor-axial bearings removed on the production line are transported to specialized areas where they are repaired. Repaired components and parts are transferred to the traction motor assembly production line, and the frame is transferred to next position frame repair lines for purging and cleaning its interior.
Auxiliary electrical machines are usually disassembled in a horizontal position. If the volume of repairs is large, it should also be carried out on conveyor lines.
Before disassembling, the machines are cleaned, purged and inspected.
Rice. 3.10. Removing the motor armature AB = = 4846eT from the frame using a bracket
Considering some design features individual auxiliary machines, the procedure for disassembling them may differ. Thus, motor fans are often performed in conjunction with control generators (for example, an NB-430 electric motor with a DK-405 control generator). When disassembling them, first remove the frame of the generator. To prevent the removed frame from falling onto the generator's anchor, it is first picked up by a crane hook. The core of the control generator installed on the NB-453 phase splitter is removed in the same way.
Then the nut securing the generator armature bushing is unscrewed from the armature shaft, the press cup of the device for pressing the armature is screwed into the bushing and, by rotating the head of the device, the armature is pressed from the electric motor shaft. To hold the removed anchor, it is also pre-hung on the crane hook.
If the control generator is connected to the fan motor using a V-belt drive, then during disassembly, first remove the transmission casing and belts, and then unscrew the bolts securing the generator bosses to the frame of the electric motor, and remove the generator.
When disassembling a motor-compressor, the engine of which does not have a second bearing shield, first remove the traverse or brush holders, disconnect the core of the electric motor from the housing and, supporting it with rope slings, carefully remove it from the anchor. Then unscrew the nut securing the gear to the armature shaft and remove the armature.
The sequence of disassembling motor generators also depends on the design of their frames. If the frame is detachable, then first remove its upper half, then remove the armature with bearing shields, remove the cross-arms of the brush holders and the brush holders themselves. At the same time, they note where and how many distance rings are installed. These rings must be installed when assembling the machine after repair, so as not to disturb the previously carried out adjustment of the bearings.
The pulleys or half-couplings are pressed off the electric motors P11, P21 and DMK, the collector hatch covers are removed, the brushes are removed, the terminal box covers, the outer bearing covers are removed and, by applying light blows with a hammer through the wooden spacer along the edges of the bearing shield, the shield is removed from the frame. Remove the anchor and press the bearings off it. On the front bearing shield, unscrew the bolts securing the traverse and remove it.
At the voltage divider, first remove the control generator (this operation is performed in the same way as when removing the generator from the fan motor shaft), remove the fan, disconnect the brush holder wires, place the voltage divider with the end of the shaft on the generator side up, press out the bearing shield and behind the eye using The crane pulls out the anchor. Then set the voltage divider frame in a horizontal position and press out the second bearing shield. The anchor removed from the frame is placed on a rack and the bearing is pressed from it using a screw tie.
For three-phase asynchronous motors, remove the protective grids, unscrew the oil lines, unscrew the bolts securing the bearing shield to the frame from the side of the free end of the shaft, and remove it using squeezing bolts. The second bearing shield is removed in the same way.
To prevent possible damage to the stator and rotor windings, when removing the rotor, lift it and place a press sheet 0.3-0.4 mm thick under it. Then a lever is put on the free end of the rotor shaft, lifted with a crane or hoist so that it can move freely inside the stator, the rotor is removed from the machine and placed on wooden blocks. Similarly, after first removing the speed relay, disassemble the NB-455A phase splitter.
For asynchronous electric motors AP-81-4 special device remove the fan impeller, and for electric motors AP-81-6 screw press- half coupling. Then the bearing caps are removed and the bearing shields are pressed together. The rotors are removed from the stators along with the bearings. The bearings are pressed and transferred to the roller department.
Safety rules for disassembling electrical machines. Most disassembly operations involve the use of cranes, hoists and other lifting equipment. Mooring electric machines or their individual elements is permitted only to specially trained persons who have the appropriate certificate. Before using a crane or hoist, make sure that the frames, cables and hoists are in good working order. Machines or parts moved by cranes must be raised above the floor to a specified height, and no unauthorized persons should be in the crane area.
Cleaning elements of electrical machines. Depending on their design and the materials used in them, it is performed differently. Thus, the frames and anchors of machines are first cleaned of dust and other contaminants by blowing compressed air over them in a blowing chamber. To avoid damaging the insulation, the hose tip should not be brought closer to it than 150 mm. A number of depots use special cameras (Fig. 3.11). In them, the armature 1 of the machine is placed on roller supports 2 and, when blowing, is rotated by an electric drive (not shown in the figure), which transmits torque to the armature through a rubber-coated pressure roller 3. Compressed air is supplied through an air duct 4 with nozzles that provide directed airflow of the armature. The entire installation is covered with a casing, which on one side is connected to the foundation on hinges, allowing it to be tilted. When installing or removing the anchor on the supports, it is folded back, turning around the axis of the hinge 5. To suck out dust, the chamber is connected by an air duct to the ventilation system.
Rice. 3.11. Scheme of a blowing chamber for electric machine armatures
After blowing, the anchor and frame are subjected to manual cleaning by wiping them with technical napkins or rags soaked in gasoline (when wiping insulation) or kerosene (when cleaning metal elements). A chemical method can also be used to clean anchors. The anchor is installed in a special chamber, rotated at a frequency of about 30 rpm, and a washing composition heated to 90 °C is supplied to it under a pressure of about 150 kPa (15 kgf/cm2).
The washed anchor is placed on a cart and fed into a drying oven (Fig. 3.12). Having installed the cart 8 with the anchor in the furnace chamber 7, close the door 9 and turn on the electric motor 5 of the fan. The air supplied to the fan rotor 6 from the chamber through air ducts 1 is again supplied to the chamber. In this case, the mechanical energy of the air moving in the rather narrow lower and upper air ducts 1 at a speed of up to 25/" m/s is converted into thermal energy. By adjusting the cross-sectional area of the grille 3 with the drive 4 and the air flow through the intake 2, it is possible to install any specified value in the chamber temperature regime. Typically, drying takes no more than 15 hours at a temperature of about 120 °C. Specific drying modes are adopted separately for different types of machines, depending on the class of insulation used in them.
Rice. 3.12. Scheme of a furnace for drying anchors
Bearing shields, their covers, axle boxes of motor-axial bearings and other parts of electrical machines made of ferrous metals and without leather or rubber elements are boiled in baths with an alkaline solution, washed in warm water and dried. Motor-anchor bearings are washed in a special washing machine soap emulsion heated to a temperature of 90 ° C for 25-30 minutes. Then these bearings are wiped with technical wipes and washed with gasoline or white spirit with the addition of 7% industrial oil grades 12, 20 or 30.
2.12. Repair of electrical machine windings
The winding is one of the most important parts of an electrical machine. The reliability of machines is mainly determined by the quality of the windings, therefore they are subject to requirements for electrical and mechanical strength, heat resistance, moisture resistance, etc. All winding conductors must be insulated from each other and from the machine body. The role of interturn insulation is performed by the insulation of the wire itself, which is applied to it during the manufacturing process at the factory. The insulation that separates the winding conductors from the housing is called housing insulation.
Closed grooves (Fig. 2.22, a) are used in both phase and squirrel-cage rotors of asynchronous motors. In modern machines, closed slots have slots to reduce slot dispersion (these slots cannot be used for inserting wires, which is why the slots are called closed). Conductors are placed in such grooves from the end of the core.
Rice. 2.22. :
a - closed; b - semi-closed; e - half-open; g - open with a bandage; d - open with wedge
Semi-closed grooves (Fig. 2.22, b) are used in stators of AC machines with power up to 100 kW and voltage up to 660 V, as well as in rotors and armatures of machines with power up to 15 kW. The round winding conductors are lowered into the slots one at a time through a narrow slot.
Half-open slots (Fig. 2.22, c) are used in the stators of alternating current machines with a power of 120 - 400 kW and a voltage not exceeding 660 V. Rigid coils are placed in them, two in each layer.
Open grooves with winding fastening with a wire band (Fig. 2.22, d) are used in armatures of DC machines with a power of up to 200 kW.
Open slots with fastening, wedge windings (Fig. 2.22, d) are used in armatures of DC machines with a power of more than 200 kW, rotors of synchronous machines with a power of 15-100 kW, stators of asynchronous machines with a power of over 400 kW and large synchronous machines.
Body insulation can be sleeve or continuous.
With semi-open and open groove forms, the straight part of the wires or coils with sleeve insulation is wrapped in several layers of insulating material, and to fasten the layers they are braided with insulating tapes. With a semi-closed groove shape, sleeves from several layers are placed in the grooves before laying the winding. Sleeve insulation is simple to make and takes up little space in the groove, but it can be used in machines with an operating voltage of no higher than 660 V. This is explained by the fact that at the joints between the sleeves and the tape insulation of the front parts of the coils there can be an insulation breakdown. Therefore, the windings of all machines with voltages above 1000 V have continuous insulation.
In this case, the coils or winding rods are braided insulating tape along the entire contour. The tape material is selected depending on the heat resistance class of the winding, the number of layers is determined by the operating voltage of the machine.
There are several ways to wrap conductors and winding coils with insulating tape.
Wrapping the tape staggered (Fig. 2.23, a) - no insulating layer is formed, so this method is used only for tightening the turns of the coil or holding layers of sleeve insulation.
Wrapping tape end-to-end (Fig. 2.23, b) - a continuous layer of insulation is not possible, since there may be bare sections of the coil at the joints. Such insulation is used only to protect the grooved parts of the coil.
IN 
Rice. 2.23. : a - staggered; b - butt; c - overlap
Wrapping the tape with an overlap (Fig. 2.23, c) - the main insulation of the coil or rod is formed. In this case, the previous turn of the tape is overlapped by 1/3, 1/2 or 2/3 of its width. Most often, an overlap of 1/2 the width of the tape is used. In this case, the actual insulation thickness is twice as large as the calculated one.
In addition to the interturn and body insulation of the coils, additional insulating gaskets are used in the windings: at the bottom of the groove, between the layers of the windings, under the wire bands, between the frontal parts. These gaskets are made from electrical cardboard, varnish fabric and insulating films, and in machines with heat-resistant insulation made of fiberglass, mikafolia, flexible micanite, etc.
The heat resistance of insulation is one of its most important properties. Depending on this parameter, insulating materials are divided into seven classes: Y (90 °C), A (105 °C), E (120 °C), B (130 °C), F (155 °C), N (180 °C), C (more than 180 °C).
The dielectric properties of insulation are characterized by its electrical strength and the amount of electrical losses. Mica-based materials have high electrical strength. For example, the electrical strength of mica tape, depending on the brand and thickness, is 16 - 20 kV/mm, of unimpregnated cotton tape - only 6, and of glass tape - 4 kV/mm.
The electrical strength of insulating materials can be significantly reduced as a result of deformation during the manufacture of windings. After impregnation with appropriate solutions, the electrical and mechanical strength of some insulating materials increases.
For the windings of electrical machines, wires with fiber, enamel and combined insulation and bare wires of round, rectangular and shaped sections are used.
Wires with enamel insulation round and rectangular section are increasingly being used instead of fiber insulated wires because enamel insulation is thinner than fiber insulation.
The winding of an electric machine consists of turns, coils and coil groups.
A turn is two conductors connected in series, placed under adjacent opposite poles. A turn can consist of several parallel conductors. The number of turns depends on the rated voltage of the machine, and the cross-sectional area of the conductors depends on its current.
A coil is several turns, laid with corresponding sides in two grooves and connected to each other in series. The parts of the coil that lie in the grooves of the cores are called slotted or active, and those located behind the grooves are called frontal.
Coil pitch is the number of groove divisions enclosed between the centers of the grooves into which the sides of the turn or coil fit. The coil pitch can be diametrical or shortened. A pitch equal to the pole division is called diametrical, and a pitch slightly smaller than the diametrical pitch is shortened.
A coil group consists of several series-connected coils of the same phase, the sides of which lie under two adjacent poles.
Winding - several coil groups laid in grooves and connected according to a certain pattern.
The windings of electrical machines are divided into loop, wave and combined. Depending on the method of filling the groove, they can be single-layer or two-layer. With a single-layer winding, the side of the coil occupies the entire height of the groove, and with a double-layer winding - only half, the second half is filled by the corresponding side of the other coil.
Main type stator winding Asynchronous machines have a two-layer winding with a shortened pitch. Single-layer windings are used only in small-sized electric motors.
In Fig. Figure 2.24 shows the unfolded and frontal (end) diagrams of a two-layer three-phase winding. The sides of the coils in the groove part are indicated by two lines - solid and dashed. The solid line represents the side of the coil, which is placed in the upper part of the groove, and the dashed line represents the lower side of the coil, which is placed in the bottom of the groove. The breaks in the vertical lines indicate the numbers of the core grooves. The lower and upper layers of the frontal parts are depicted with dashed and solid lines, respectively.
The beginnings of the first, second and third phases are designated CI, C2, SZ (according to the old but widely used GOST) or Ul, VI, W1 (according to the new GOST), and the ends of these phases are respectively C4, C5, C6 or U2, V2, W2. The diagram indicates the type of winding, and also gives its parameters: z - number of slots; 2p - number of poles; y - winding pitch along the slots; a is the number of pairs of parallel branches in phase; t - number of phases; phase connection method - Y - star, L - triangle.
Stator windings are made of single-layer and double-layer. Winding of single-layer windings is carried out mechanized on special machines.
Single layer windings have different shapes, and the frontal parts of one coil group have the same shape, but different sizes (Fig. 2.25). To lay the winding in the slots of the stator core, the frontal parts of the coils are placed around the circumference in two or three rows. The most common are single-layer two- and three-plane windings (the frontal parts of the winding are located on two or three levels.
The rotors of asynchronous motors are made with a short-circuited or phase winding. Short-circuited windings of electrical machines of old designs were made in the form of a “squirrel cage” from copper rods, the ends of which were sealed in holes drilled in copper short-circuited rings (see Fig. 2.3). In modern asynchronous electric machines with a power of up to 100 kW, the short-circuited rotor winding is formed by filling its slots with molten aluminum.
C1 C6 C2 C4 NW C5
Rice. 2.25. (r = 24; p = 2): a - with an even number of pole pairs; b - location of the frontal parts; c - with an odd number of pairs of poles; d - location of the frontal parts
In phase rotors of asynchronous motors, wave or loop windings are most often used. The most common are wave windings, the advantage of which is the minimum number of intergroup connections. The main element of the wave winding is a regular rod. A two-layer wave winding is made by inserting two rods from the end of the rotor into each of its closed or semi-closed grooves. The wave winding diagram of a four-pole rotor, which has 24 slots, is shown in Fig. 2.26, a. The pitch of the wave winding is equal to the number of slots divided by the number of poles. For the circuit shown in Fig. 2.26, a, it will be equal to 6. This means that the upper rod of groove 1 approaches the lower rod of groove 7, which, with a winding pitch of 6, is connected to the upper rod of groove 13 and the lower rod of groove 19. To continue the winding with a pitch equal to 6, it is necessary to connect the lower rod of groove 19 with the upper rod of groove 1, which means short-circuiting the winding, which is unacceptable. To avoid this, shorten or lengthen the winding pitch by one groove. Wave windings with a shortened pitch by one slot are called windings with shortened transitions, and with an increased pitch by one slot - windings with extended transitions.
In the winding diagram, the number of slots per pole and phase is two, so it is necessary to make two bypasses of the rotor, and to form a four-pole winding there are not enough connections on the opposite side of the rotor, which can be obtained by bypassing it, but in the opposite direction.
In wave windings, a distinction is made between the front winding pitch on the side of the leads (slip rings) and the rear winding pitch on the side opposite to the slip rings. Bypassing the rotor in the opposite direction, in this case the transition to the rear step, is achieved by connecting the lower rod of the groove 18 with the lower rod, which lags behind it by one step. Next, two rounds of the rotor are made. Continuing to bypass the rotor backwards, the lower rod of groove 12 is connected to the upper rod of groove 6. Further connections are made in the same way. The lower rod of groove 1 is connected to the upper rod of groove 19, which (as can be seen from the diagram) is connected to the lower rod of groove 13, which in turn is connected to the upper rod of groove 7. The second end of the upper rod of this groove goes to the output, forming the end of the first phase .
The windings of the phase rotors of asynchronous motors are connected mainly by a “star” with the three ends of the winding being connected to the slip rings. The rotor winding terminals are designated PI, P2, РЗ (according to the old GOST) or Kl, LI, Ml (according to the new GOST), and the ends of the winding phases are respectively P4, P5, P6 or K2, L2, M2.
The jumpers that connect the beginnings and ends of the rotor winding phases are indicated in Roman numerals, for example, in the first phase, the jumper that connects the beginning of P1 and the end of P4 is designated I-IV, P2 and P5 - II-V, RZ and P6 - III-VI . 
For armatures of DC machines, loop and wave windings are used. A simple armature wave winding (Fig. 2.26, b) is obtained by connecting the output ends of the section with two collector plates AC and BD, the distance between which is determined by double pole division (2t). When making a winding, the end of the last section of the first bypass is connected to the beginning of the section adjacent to the one from which the bypass was started, and then the bypasses continue along the armature and commutator until all the slots are filled and the winding is closed.
Preparing windings for repair. Winding repairs are carried out by specially trained workers at the winding sections of a repair department or enterprise. Preparing machines for repair involves selecting winding wires, insulating, impregnating and auxiliary materials. The list of materials required to repair the windings is included in the operational documentation of the electrical machine.
To detect short circuits in the winding between the turns of one coil or wires of different phases, special devices are used. Having determined the nature of the winding malfunction, its repair begins.
The technology for overhauling electrical machine windings includes the following basic operations:
winding disassembly;
cleaning the core grooves from old insulation;
repair of the core and mechanical part of the machine;
cleaning the winding coils from old insulation;
preparatory operations for the manufacture of windings;
production of winding coils;
insulation of the core and winding holders;
laying the winding in the groove;
soldering winding connections;
fastening the winding in the grooves;
drying and impregnation of the winding.
Repair of stator windings. The manufacture of the stator winding begins with winding individual coils on a template. To choose the right template size, you need to know the main dimensions of the coils, mainly their straight and frontal parts. The dimensions of the winding coils of dismantled machines are determined by measuring the old winding.
Coils of random stator windings are usually made on universal templates (Fig. 2.27). This template is a steel plate 1, which is connected to the spindle of the winding machine using a sleeve 2 welded to it. The plate has the shape of a trapezoid. Its slot contains four studs secured with nuts. When winding coils of different lengths, the pins are moved in the slots. When winding coils of different widths, the pins are rearranged from one slot to another.
In the stator windings of AC machines, usually several adjacent coils are connected in series and they form a coil group. To avoid unnecessary solder connections, all coils of one coil group are wound with a single wire. Therefore, rollers 4, machined from textolite or aluminum, are put on the studs 3. The number of grooves on the roller is equal to the largest number of coils in the coil group; the dimensions of the grooves must be such that all the coil conductors can fit into them.
Rice. 2.27.: 1 - plate; 2 - bushing; 3 - hairpin; 4 - rollers
Sometimes when repairing motor windings, it is necessary to replace missing wires with wires of other brands and cross-sections. For the same reasons, instead of winding 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 motors being repaired, the slot fill factor is first checked (before winding the coils), which should be 0.7 - 0.75.
The coils of a two-layer winding are placed in the grooves of the core in groups, as they were wound on the template. The wires are distributed in one layer and the sides of the coils are placed, which are adjacent to the groove. The other sides of the coils are not placed in the grooves until the bottom sides of the coils are placed in all the grooves (Fig. 2.28). The following coils are placed with their upper and lower sides simultaneously. Between the upper and lower sides of the coils, insulating gaskets made of electrical cardboard, bent in the form of brackets, are installed in the grooves, and between the frontal parts - made of varnished fabric or sheets of cardboard with pieces of varnished fabric glued to them.
When repairing electrical machines of old designs with closed slots, it is recommended that before dismantling the winding, it is recommended to take its actual winding data (wire diameter, number of wires in the slot, winding pitch along the slots, etc.), and then make sketches of the frontal parts and mark the stator slots (these data may be needed when restoring the winding). 
Rice. 2.28. 
Rice. 2.29. : 1 - steel mandrel; 2 - sleeve
The manufacture of windings with closed slots has a number of features. The groove insulation of such windings is made in the form of sleeves made of electrical cardboard and varnished fabric. First, a steel mandrel 1 is made according to the dimensions of the machine grooves, which consists of two opposing wedges (Fig. 2.29). The mandrel should be smaller than the groove by the thickness of the sleeve 2. Then, according to the dimensions of the old sleeve, blanks of electric cardboard and varnished fabric are cut into a complete set of sleeves and they begin to manufacture them. Heat the mandrel to 80 - 100 °C and tightly wrap it with a workpiece impregnated with varnish. Cotton tape is tightly laid on top of the workpiece with a full overlap. After the mandrel has cooled to ambient temperature, the wedges are spread and the finished sleeve is removed. Before winding, the sleeves are placed in the grooves of the stator, and then filled with steel rods, the diameter of which should be 0.05 - 0.1 mm larger than the diameter of the insulated winding wire. A piece of wire needed to wind one coil is cut from the coil. A long wire complicates winding, and the insulation is often damaged due to frequent pulling it through the groove.
Broach winding is usually carried out by two winders, which are located on both sides of the stator (Fig. 2.30). Frontal insulation
The windings of machines for voltages up to 660 V, intended for operation in a normal environment, are made with LES glass tape, with each subsequent layer semi-overlapping the previous one. Each coil of the group is wound starting from the end of the core. First, tape the part of the insulating sleeve that protrudes from the groove, and then the part of the coil to the end of the bend. The middles of the group heads are completely overlapped with glass tape. The end of the tape is fixed to the head with glue or tightly sewn to it. The winding wires, which lie in the groove, are held using groove wedges made of beech, birch, plastic, textolite or getinax. The wedge should be 10 - 15 mm longer than the core and 2 - 3 mm shorter than the groove insulation and at least 2 mm thick. To ensure moisture resistance, wooden wedges are “cooked” for 3–4 hours in drying oil at 120–140°C.
Rice. 2.30. Pull winding of the stator winding of an electric machine with closed slots
The wedges are driven into the grooves of medium and small machines with a hammer and using a wooden extension, and into the grooves of large machines with a pneumatic hammer (Fig. 2.31). Then the winding circuit is assembled. If the winding phase is wound with separate coils, they are connected in series into coil groups. 
Rice. 2.31. : 1 - wedge; 2 - groove insulation; 3 - extension
The beginning of the phases is taken to be the conclusions of the coil groups, which come out of the grooves located near the output panel. These leads are bent to the stator housing and the coil groups of each phase are pre-connected, and the ends of the wires of the coil groups, stripped of insulation, are twisted.
After assembling the winding circuit, check the electrical strength of the insulation between the phases and on the housing, as well as the correctness of its connection. To do this, use the simplest method - briefly connect the stator to the network (127 or 220V), and then apply a steel ball (from a ball bearing) to the surface of its bore and release it. If the ball rotates around the circumference of the bore, then the circuit is assembled correctly. This check can also be carried out using a pinwheel. A hole is punched in the center of the tin disk, secured with a nail at the end of a wooden plank, and then this pinwheel is placed in the stator bore, which is connected to the electrical network. If the circuit is assembled correctly, the disk will rotate.
The correct assembly of the circuit and the absence of turn short circuits in the windings of the machines being repaired are also checked using the El-1 electronic device. Two identical windings or sections are connected to the apparatus, and then, using a synchronous switch, periodic voltage pulses are applied to the cathode ray tube of the apparatus. If there is no damage in the windings, the voltage curves on the screen are superimposed on one another, but if there are defects, they bifurcate. To detect grooves in which short-circuited turns are located, use a device with two U-shaped electromagnets for 100 and 2000 turns. The fixed electromagnet coil (100 turns) is connected to the terminals of the device, and the moving electromagnet coil (2000 turns) is connected to the “Signal phenomenon” terminals. In this case, the middle handle should be placed in the extreme left position “Working with the device”. If you move both electromagnets of the device from groove to groove along the stator bore, a straight or curved line with small amplitudes will appear on the screen, which indicates the absence of short-circuited turns in the groove. Otherwise, there will be curved lines with large amplitudes on the screen.
Similarly, short-circuited turns are found in the winding of a phase rotor or armature of DC machines.
Repair of rotor windings. In asynchronous motors with a wound rotor, two main types of windings are used: coil and rod. The manufacture of random and drawn coil windings of rotors is almost no different from the manufacture of the same stator windings.
In machines with a power of up to 100 kW, rod-type double-layer wave rotor windings are mainly used. It is not the rods themselves that are damaged, but their insulation (as a result of frequent excessive heating), as well as the slot insulation of the rotors.
Usually, the copper rods of the damaged winding are reused, so after the insulation is restored, they are placed in the same grooves in which they were before the repair.
The assembly of the rotor core winding consists of three main operations: laying the rods in the grooves of the rotor core, bending the frontal parts of the rods and connecting the rods of the upper and lower rows by soldering or welding. Insulated rods that are reused come into the slots with only one bent face. The other ends of these rods are bent with special keys after being placed in the grooves. First, the rods of the bottom row are placed in the grooves, inserting them from the side opposite to the slip rings. Having laid the entire lower row of rods, their straight sections are placed on the bottom of the grooves, and the bent front parts are placed on an insulated winding holder. The ends of the bent frontal parts are tightly tightened with a temporary bandage made of soft steel wire, pressing them tightly against the winding holder. A second temporary wire bandage is wound around the middle of the frontal parts. Temporary bandages serve to prevent the rods from shifting during further bending.
The rods are bent using two special keys (Fig. 2.32).
After laying the rods of the lower row, they proceed to laying the rods of the upper row of the winding, inserting them into the grooves on the side opposite to the slip rings. Then temporary bandages are applied. The ends of the rods are connected with copper wire to check that there is no short circuit to the body. If the test results are positive, continue winding assembly, the ends of the upper rods are bent in the opposite side. The bent frontal parts of the upper rods are also secured with two temporary bands. 
Rice. 2.32. :
o - plate; b - “language”; c - reverse wedge; g - corner knife; d - drift; e - hatchet; ok, a - wrenches for bending rotor rods
After laying the rods of the upper and lower rows, the rotor winding is dried at 80 - 100 ° C in an oven or drying cabinet. Then the insulation of the dried winding is tested.
The final operations of manufacturing the rod winding of the rotor of the machine being repaired are connecting the rods, driving the wedges into the grooves and banding the winding. To increase the reliability of machines, they use hard soldering to connect rods.
The windings of phase rotors of asynchronous motors are connected mainly by a star.
Most asynchronous motors with a power of up to 100 kW are manufactured with a squirrel-cage rotor, which is made of aluminum by casting.
Repairing a cast rotor with a damaged rod consists of recasting it after smelting the aluminum and cleaning the grooves. Chills are used for this purpose.
At large electrical repair plants, squirrel-cage rotors are filled with aluminum using a centrifugal or vibration method, and injection molding is also used.
Repair of armature windings. The main malfunctions of armature windings: connection of the winding to the housing, interturn short circuits, breaks in the windings, mechanical damage to soldering.
When preparing the armature for repair, the old bands are removed, the connections to the commutator are unsoldered, and the old winding is removed, having previously recorded all the data necessary for the repair.
In DC machines, rod and template windings of armatures are used. The core windings of the armatures are performed in the same way as the core windings of the rotors.
To wind sections of the template winding, insulated wires are used, as well as copper busbars, which are insulated with varnished cloth or mycol tape. Template winding sections are wound on universal templates, which allow you to wind and then stretch a small section without removing it from the template. Stretching of armature sections of large machines is carried out on special machine-driven machines. Before stretching, the section is secured by temporarily wrapping it with a single layer of cotton tape to ensure that the section forms 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, which are turned towards the collector, as well as the distances from the edge of the core to the transition of the straight (slot) part to the front part are the same. After laying the entire winding, the wires of the armature winding are connected to the collector plates by soldering using POSZO solder.
The quality of soldering is checked by external inspection, measuring the transition resistance between adjacent plates, and passing the operating current through the armature winding. For high-quality soldering, the contact resistance between all pairs of plates must be the same. When passing the rated current through the armature winding for 20 - 30 minutes, local heating should not occur.
Repair of pole coils.
Most often, the coils of additional poles that are wound with a rectangular copper busbar, either plaza or on an edge, are damaged. Usually the insulation between the turns of the coil is damaged. When repairing, the coil is rewound to winding machine(Fig. 2.33, a), and then insulated on an insulating machine (Fig. 2.33, b). The insulated coil is tied together with cotton tape and pressed. To do this, put an end insulating washer on the mandrel, place the coil on it and cover it with a second washer. Then the coil is compressed on the mandrel, connected to a welding transformer, heated to 120 ° C and, compressing it, pressed again, after which it is cooled in the pressed position on the mandrel to 25 ° C. The cooled coil removed from the mandrel is coated with air-drying varnish and kept for 10 - 12 hours at 20 - 25 °C. 
Rice. 2.33. :
a - for winding coils of strip copper; b - for insulating the wound coil; 1, 4 - micanite and cotton tapes; 2 - template; 3 - copper bus;
5 pole coil
The outer surface of the coil is insulated with asbestos and then micanite tape and varnished. The finished coil is put on an additional pole and secured with wooden wedges.
Drying and impregnation of windings. Some insulating materials (electric cardboard, cotton tapes) are hygroscopic. Therefore, before impregnation, the windings of stators, rotors and armatures are dried in special ovens at 105 - 200 ° C. You can also use infrared rays, the source of which is special incandescent lamps.
Dried windings are impregnated with varnish in special heated baths, which are installed in a separate room equipped supply and exhaust ventilation and necessary fire extinguishing equipment.
For windings, impregnating varnishes of air or oven drying are used, and in some cases, organosilicon varnishes. Impregnating varnishes must have low viscosity and high penetrating ability and maintain insulating properties for a long time.
The windings of electrical machines are impregnated once, twice or three times, depending on the operating conditions and the requirements placed on them. During the impregnation process, it is necessary to constantly check the viscosity and thickness of the varnish, as the solvents evaporate and the varnish thickens. At the same time, its ability to penetrate into the insulation of the winding wires located in the grooves of the stator or rotor core is significantly reduced. Therefore, a solvent is periodically added to the impregnation bath.
After impregnation, the windings of electrical machines are dried in special chambers with natural or forced ventilation thermal air. Heating can be electric, gas, steam. Electrically heated drying chambers are the most common.
At the beginning of drying (1 - 2 hours), when the moisture retained in the windings quickly evaporates, the exhaust air is completely released into the atmosphere. During the subsequent drying hours, part of the exhaust warm air, containing a small amount of moisture and solvent vapor, is returned to the chamber. The maximum temperature in the chamber does not exceed 200° C.
During drying of the windings, the temperature in the chamber and the air leaving it is constantly monitored. The windings are positioned so that they are better blown with hot air. The drying process consists of heating the windings (to remove the solvent) and baking the varnish film.
When heating the windings, it is undesirable to increase the temperature above 100 - 110°C, since a varnish film may form prematurely.
During the baking process of the varnish film, it is possible to briefly (no more than 5–6 hours) increase the drying temperature of windings with class A insulation to 130–140 °C.
At large electrical repair enterprises, impregnation and drying are carried out on special impregnation and drying conveyor units.
After repair, electric machines are sent for testing.
1. What methods of winding coils with tapes are used to insulate them?
2. How are insulating materials divided into heat resistance classes?
3. What is a turn, coil, coil group and winding?
4. What types of windings are used in the stators of asynchronous motors?
5. What slots are used in electrical machines?
6. How does the universal winding template work?
7. How is the template winding placed in the slots?
8. How is bar winding made?
9. What devices are used when making armature coils?
10. How are the frontal parts of the windings insulated?
11. What malfunctions occur in pole coils?
12. Why are the windings dried?
13. Winding impregnation process.
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Troubleshooting of electrical machines
The following types of faults are possible in electrical machines:
- sparking brushes;
- overheating of windings;
- 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 commutator and brushes. The reason for this may be contamination of the brushes and commutator, wear of the brushes, burning of the commutator, loose fit of the springs, sticking of the brushes in the brush holder.
Dirt from the brushes and commutator is removed with compressed air, and in some cases with a rag soaked in gasoline. Brushes worn out by more than 60% or broken are replaced with new ones. New or poorly lapped brushes are ground into the commutator. To do this, a strip of sanding paper (Fig. 185, a) is pulled several times between the brush and the commutator. The abrasive surface of the sanding paper should be facing the brush. After grinding in, the commutator and brushes are blown with compressed air.
You cannot use emery cloth or carborundum cloth to sand brushes. To properly grind the brushes, the ends of the sanding paper must be bent downwards (see Fig. 185, a), since when bending the sandpaper upwards (Fig. 185, b), the edges of the brushes will be filed and the active width of the brushes will decrease, which can cause sparking on the commutator.
Rice. 185 - Brush grinding patterns: correct (a), incorrect (b)
If there is carbon deposits, shells and other local defects, the collector is ground to lathe or sand with fine grit grinding wheels. The commutator must have a polished surface, so after turning and grinding it is polished, as a result of which scratches resulting from processing the commutator (with a cutter or stone) are eliminated. Polish the commutator at rated speed (motor rotor) using No. 00 sanding paper.
To polish the collector, 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 such that it can fit freely between two adjacent cross-beams. The block is pressed against the rotating commutator. Once a smooth surface is obtained, the collector is cleaned and blown with compressed air.
Rice. 186 - Collector polishing pad
The pressure on the brush created by the brush holder spring must correspond to a certain pressure. To reduce mechanical losses on the commutator, it is recommended to set the minimum pressure at which the brushes operate without sparking. It should be taken into account that the higher the rotation 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 pressing force of the brushes is checked using a dynamometer (1) (Fig. 187), attached to the brush holder lever (2), which presses the brush (3) to the commutator (4). To determine the pressing force, it is necessary to place a sheet of paper (5) between the brush and the commutator and gradually pull back the dynamometer. At the moment the paper is freely pulled out from under the brush, the dynamometer will show the amount of pressure of the brush on the commutator.
Rice. 187 - Measuring brush pressing force with a dynamometer
The correct installation of the brushes must be checked after each grinding of the commutator. If the brushes are not positioned correctly, the machine begins to spark at partial load. The car does not spark when idling. As the load increases, a circular fire may be observed along the collector.
The correct position of the traverse is checked inductively with the car stationary. Direct current is supplied to the disconnected field winding through a rheostat from the battery. The current in the winding should not exceed approximately 5...10% of the rated value. A 45...60 mV millivoltmeter with zero in the middle of the scale is connected to the armature terminals. At the moments of closing and opening of the excitation current, an electromotive force (emf) is induced in the armature and the instrument needle deviates in one direction or another depending on the position of the brushes. With the brushes in the desired position (neutral), e.g. d.s. must be equal to zero. The traverse with brushes is moved until the required position of the brushes is achieved. It is recommended to check the correct position of the traverse at different anchor positions. The armature should be turned in the same direction to avoid possible movement of the brushes in the brush holders influencing the instrument readings. The final correct position of the traverse is checked during testing of the machine on a bench.
Besides, cause of sparking brushes There may be an unequal distance around the circumference of the commutator 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 adjacent 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). During repairs, it is necessary to replace all brushes and install those brands recommended by the manufacturer of electrical machines.
Elevated heating (overheating) of windings The electrical machine is installed during the period of pre-repair tests. Uniform overheating of the entire machine in the absence of other signs of malfunction indicates its overload. In this case, you should first check whether the actual load corresponds to the rated operating mode of the machine. Deterioration of ventilation conditions due to blockage ventilation ducts fan impeller may also cause the machine to overheat.
Damage to the pole windings leads to uneven heating. In the windings of the poles, the transitions, the lead ends of the coils and the places where the lead ends pass through the housing are most often damaged. The most common defects include short circuit of the windings to the housing, breakage or poor contact in the windings, connection between the turns.
After damage is detected, the windings are rewound. To do this, remove the old winding, clean the grooves from burrs, paint them with varnish and insulate them with electric cardboard, pressboard and varnished cloth.
Methods for eliminating defects in pole windings depend on the nature of the damage. Breaks, as well as poor contact in external places accessible for repair, are eliminated by soldering. To find a short to the housing, the coil with a defect is removed from the pole core and the places of contact with the pole and the frame are inspected.
Short circuits in windings poles, if they are not at the output ends, are eliminated by partial or complete rewinding. The coils are unwinded from the coil and inspected at the same time. If the insulation of the coils, with the exception of the points of connection with the body or the short circuit between the turns, is not damaged and is in satisfactory condition, then only the damaged places are insulated, and the coil is not completely rewinded.
If damage to the pole windings is caused by wet insulation, then the coil is dried.
When there is a short circuit in the armature winding, the generator is poorly excited, the engine does not develop rated speed, and in some cases the armature rotates in jerks. When the generator is excited from an external current source, the armature immediately after connecting the field winding becomes very hot and smoke appears. The collector plates connected to the defective heating armature winding burn out. In this case, short circuits may 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 short circuits in 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 convenient when testing armatures with equalizing connections. The method consists of applying direct current to two adjacent collector plates (1) (Fig. 188) using probes (2), and using probes (3) to measure the voltage drop across the same pair of collector plates. It is convenient to use a rechargeable battery as a current source, providing a current of 5...10 A through a rheostat connected in series with the armature. Then, in the case of a loop winding, if there is a short circuit in the section connected to the pair of plates being tested, its resistance will be less and the voltage drop at one and the same current will also be less than on another 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 the turns and armature windings
A short-circuit in the armature or commutator winding to the body during operation of the machine is not detected unless there is a short-circuit in one of the network wires. In the presence of such a short circuit (if the machine body is not isolated from the ground), the short circuit of the winding to the body forms a closed circuit. If one of the network wires is not grounded, a closed circuit can only be formed when the winding is shorted to the housing in two places.
You can determine whether the winding is shorted to the housing using a megger or a test lamp (Fig. 189). In the latter case, one end from 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 lighting of the lamp. With this method, the lamp lights only when there is good contact at the connection point.
Rice. 189 - Diagram for finding the junction of the armature winding with the housing
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 pitch. One conductor from the millivoltmeter is connected to the armature shaft, and the end of the other one touches all the collector plates in turn. If you check an 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 if the contact is poor, and also when it is not the collector plate that has a short to the housing, but the section connected to this plate.
Since when checking the entire armature, the highest possible voltage acting on the device may 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 device needle can be achieved by adjusting the current strength by connecting the device through a rheostat.
The location of the short circuit to the housing can be found by moving the sections one by one where the winding exits the grooves and at the same time measuring the insulation resistance with a megger. Moving the sections creates a change in contact, and therefore a change in resistance. Instead of a megger, you can use a test lamp, turning it on between the commutator and the armature shaft. The defect is detected by the lamp blinking.
In cases where the above methods do not produce results, it is necessary to divide the winding into parts by unsoldering it. Having divided the winding into two parts, check each part separately with a megger. Having detected a short circuit to the body in one of the halves, the ends of the other are left untouched, and the damaged half is again divided into two parts, and so on until the section with the short circuit to the body is precisely determined.
Damage is repaired in a variety of ways. For example, a break or poor contact in the winding (in cockerels and clamps) and the collector is eliminated by resoldering the winding in the indicated places; if the break occurs in the conductor itself, then the rod or section is replaced with new ones.
Most often, a short circuit to the housing occurs at the places where the sections exit the grooves. This defect is eliminated by installing under the section small wedges made of insulating material (fiber, dry beech) or a gasket, a varnished lining made of letheroid, electrical cardboard, mica, etc. A short circuit 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 circuit to the housing caused by dampening of the insulation is eliminated by drying. If there is a short circuit to the housing in several sections and, in addition, the insulation of other sections is poor, then the entire armature winding is rewinded. If the collector is connected to the housing, it must be disassembled and repaired.
A short circuit in the armature winding between non-adjacent sections and, in general, a short circuit of a large number of sections are less common than short circuits within the section itself or between the ends of sections on the collector. Therefore, before you begin to eliminate short circuits, you must 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. Re-insulating the fault point can only be limited to the 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.
The following types of faults are possible in asynchronous electric motors:
- stator overheating;
- overheating of the stator and rotor windings;
- abnormal engine speed;
- abnormal noise in the car.
Stator overheating can be observed when the network voltage is higher than the nominal one. To eliminate this malfunction, it is enough to reduce the mains voltage to the nominal value or improve the engine ventilation.
Increased local heating when the engine is idling and at rated mains voltage can be caused by burrs formed during filing or as a result of the rotor touching the stator during engine operation. The malfunction is eliminated by removing burrs; For this purpose, the short circuits are processed with a file, the connected steel sheets are separated, varnished with insulating varnish, followed by air drying.
In AC windings, short circuits are possible between the turns of one coil, coils of the same phase and coils of different phases. The main sign by which a short circuit can be found in AC windings is increased heating of the 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 charring of the 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 voltage) 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 change depending on the position of the rotor relative to the stator, then this indicates a short circuit in the stator winding. When there is a short circuit in the rotor winding (if the stator winding is working), the voltage between the rotor rings will be unequal and will not change depending on the position of the rotor.
After it has been 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 occurs between two phases, then the connection point is found in the same way as the previous one, disconnecting the windings in phases. The coils of one of the phases having a connection are divided into two parts and the presence of connections of each such half with the second phase is checked with a megger. 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 division method used when a short circuit is found in windings that have 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 most often occur in the end parts of the winding or connecting conductors, sometimes it is possible to immediately find the connection point by moving the end parts while simultaneously checking with a megger.
Overheating of the stator winding can occur when the motor is overloaded or its normal insulation is damaged. Reducing the voltage at the motor terminals below the rated voltage also causes an overload of the motor with current. Overheating of the winding will occur if the stator windings are incorrectly connected in a delta rather than a star configuration.
The reason for strong local heating of the stator winding may be an interturn connection in the winding or a short circuit between two phases. Signs of malfunction: unequal current strength in individual phases, the motor makes a loud noise and develops reduced torque.
Winding repair
If interturn short circuits or short circuits to the housing 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 removal of defective coils from the grooves, the stator is heated to 70...80 ° C. Then, using a drift and a wooden hammer, the textolite wedges are knocked out, the stator windings are cut and removed using intercoil connections, the coils are disconnected and removed from the grooves. The stator grooves are cleaned of old insulation, and the condition of the steel packages is checked.
The coils are wound with insulated wire of the appropriate grade 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 onto a boat template, which has a device for securing the ends of the wires. One of the sides of the template is removable for removing the coil after winding. When winding coils of 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 arrangements for placing paper insulating pads between layers of coils and laying mechanisms that lay the conductors in the correct rows.
After winding is completed, an electrical cardboard gasket is placed around the perimeter of the coil and the coil is tied at the cutouts in the template. The ends of the wires are cut at the distance indicated in the drawing.
The body insulation of the coils is made of several layers of varnished fabric or mica tape. To give the required shape and solidity, the turns of the groove part of the coil are lubricated with adhesive glyphthalic or shellac varnish before applying body insulation. Then the groove 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 binding substances of the adhesive varnish soften and fill the pores of the insulation; when cooled, they harden and hold the coil conductors together. The coils are secured in the grooves with textolite wedges driven in with a wooden hammer.
The coils placed in the grooves are connected by soldering or flash welding. Flash welding is carried out 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 and above. The ends of the wires to be welded are pre-twisted and connected to one of the terminals of the transformer, and a carbon electrode is connected to the other terminal.
In electric motors used on refrigerated rolling stock, winding wires made of copper wire are most widely used. Some types of electric motors use aluminum wires, which are significantly inferior to copper wires in terms of mechanical strength and electrical conductivity.
Winding wires are made with fiber, enamel and combined insulation. The material for fiber insulation is paper (cable or telephone), cotton yarn, natural and artificial silk (nylon, lavsan), asbestos and glass fibers. They are applied in one or several layers in the form of a winding or braid (stocking). For enamel insulation, various organic compounds are used (polyvinyl acetate, silicone resins, etc.).
Brands of winding wires are conventionally designated by letters. In some brands, the letter designation is followed by the number “1” or “2”: the number “1” indicates normal insulation thickness, the number “2” indicates reinforced thickness.
Designation of winding wire brands starts with the letter P (wire). Fiber insulation is designated by the letters: B - cotton yarn, Sh - natural silk, ShK and K - artificial silk, nylon, C - fiberglass, A - asbestos fiber. The letters O and D indicate the number of insulation layers (one or two). For aluminum winding wires, the letter A is added to the end of the designation. For example, the PBB brand means: copper winding wire with insulation made of two layers of cotton yarn.
Enamel insulation winding wires is designated 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, the PEL brand means: copper wire coated with varnish-resistant enamel.
Combined insulation is also used, which consists of enamel insulation and insulation made of fibrous materials placed 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 are designated with the letter K (for example, PSDK brand wire).
Three-phase stator windings of alternating current machines are conventionally divided into single-layer, when the coil side occupies the entire slot, and double-layer, when the coil side occupies half the slot in height, i.e., two sides of the coil are placed in each slot.
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 first phase coils are first placed in the slots, and the upper sides are temporarily left raised. Then both sides of the second and third phase coils are sequentially placed in the grooves. In this case, one side of the coil is placed in bottom part the next unfilled groove, and the other - the upper part of the groove, already half filled with winding.
After laying, the lower and then the upper windings are compacted at the bottom of the groove using a special mandrel and a hammer. An insulating pad is placed between the lower and upper layers of the winding, the upper layer of the winding is covered with insulation and reinforced with a wedge. Electric cardboard is placed between the frontal parts of the phase coils. The laid coils are connected by soldering, and the joints are insulated. After laying the windings, check that the coils are connected correctly.
Collectors repair
If tracks from brush activation are found on the surface of the commutator, the commutator is ground, ground and polished. For grinding abrasive wheels are used, which include pumice impregnated with kerosene. Polishing the commutator wooden concave block covered with glass paper.
In order to avoid protrusion of micanite gaskets above the surface of the collector, it is increased in price. Increase in price consists in the fact that the micanite insulation between the collector plates is cut to a depth of 0.5...1.5 mm, and longitudinal tracks are formed on the surface of the collector. Increase in price is necessary because mikanite is harder than commutator copper, and when the copper plates wear out, micanite protrudes onto the surface of the commutator, which impairs the operation of the brushes and the switching of the machine.
Expansion of the collectors of low and medium power vehicles (converters), undercar generators is carried out manually using a scraper made of hacksaw blade(Fig. 190). The expansion of high-power machine manifolds is carried out on a machine using a milling cutter or a special portable machine with a flexible hose.
Rice. 190 - Increase in cost of collector insulation: 1 - collector; 2 - cutter; 3 - electric motor; 4 - longitudinal movement support; 5 - vertical movement support; 6 - flywheel; 7 - roller
After milling, the edges of the collector plates are removed with a scraper. The chamfers are removed at an angle of 45° with a size of 0.5 mm (Fig. 191) and the collector is thoroughly cleaned of residual mica and copper.
Rice. 191 - Chamfering commutator plates
Sometimes it is necessary to remove one or more copper plates that have significant copper melting or burnout. The causes of such damage can be short circuits between the plates, breakdown of micanite plates, breakage of cockerels in the immediate vicinity of the junction with the plates.
Technical conditions for the repair of electrical machines allow the replacement of no more than five plates. Replacing collector plates is a complex type of repair; removal of even one plate can lead to a violation of the solidity of the collector and loss of geometric correct form, unless special measures are taken and appropriate devices are not used to secure the collector when removing the plate. A tension disc can serve as one of these devices.
The commutator runout in a repaired machine is measured with an indicator after rotating the armature at rated speed. The collector runout should be no more than 0.03...0.04 mm. Exceeding these standards causes severe 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 runout of the collector is detected, the machine is disassembled and the bolts holding the plates are tightened, first in a cold state, then heated to 100...110°C. After this, the surface of the collector is ground, polished and value-added.
The most common damage to contact rings is the following: wear (operation) of the contact surface and violation of the insulation of the contact bolts, melting and burnout of sections 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 onto it, followed by machining. The same method can be used to restore partially worn plates.
Restoring the insulation of slip rings with a cold fit on the bushing 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 electrical cardboard (3) with a thickness of 0.1...0.4 mm are inserted. To prevent the insulation layers from getting knocked down during crimping, a split sleeve (2) rolled up from sheet steel 1.5 mm thick is inserted inside. The sleeve (1) is pressed into the sleeve hole using a hydraulic press.
Rice. 192 - Slip ring assembly
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 landing contact rings, in contrast to the above repair method, the sleeve is not pressed into the contact rings, but the contact rings are hot and pressed onto an insulated sleeve.
For bushing insulation use molding micanite with a thickness of 0.25...0.35 mm, cut into strips, coated with shellac or glyphthalic varnish, dried in air for 0.5...1 hour and tightly placed on a 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 internal diameter of the slip rings by 1.5...2 mm. Then the insulation is wrapped in two or three layers of paper, tightly pulled together with a steel clamp 2...3 mm thick, 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 glyphthalic.
After the bushings have cooled, any traces of varnish are removed from the insulation and machined. The diameter of the machined insulation must exceed the internal diameter of the slip rings by the amount of interference.
Contact bolts are insulated with micafolium or molding micanite with a thickness of 0.2...0.3 mm. To do this, the surface of the bolt is cleaned of old insulation, lubricated with glyphthalic 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, remove the keeper tape from the insulation, clean the insulation from irregularities and varnish stains, process it to the required size manually or on a machine, and paste it with one or two layers of electrical cardboard.
Brush holders and traverses are carefully inspected, the condition of their insulation and the serviceability of the 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, brushes of the wrong brand can cause severe sparking on the commutator.
New brushes are ground into the commutator.
Grinding in brushes manually is a very labor-intensive operation, so when replacing brushes they are ground outside the machine on a special machine (Fig. 193). The same machine is used to check the correct placement of brushes around the circumference of the commutator. A worm screw (7), mounted on the end of the electric motor shaft (1), rotates the shaft (3) through a 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 traverses for brush holders of different types of machines. A drum (5) is placed on the end of the shaft, the outer diameter of which is 1 mm less than the diameter of the collector. Marks are marked on the drum, which are used to check the placement of brushes around the circumference of the commutator. Then remove the brushes from the brush holder holders and wrap the drum with glass paper, which is secured with 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 traverses, 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. The pin insulation and insulating washers must not be damaged. Check the presence of locking bolts, pin bolts and other fasteners. Faulty parts of brush holders (current-carrying bolts, screws, pressure fingers, broken and insufficiently stiff springs) are replaced.
When the commutator rotates, the brushes vibrate in the cages and wear them out. An increase in the gap between the brush and the brush holder cage leads to distortion of the brush in the cage and disruption of its contact with the commutator. The developed holes in the body of the brush holders are restored by galvanic method or surfacing with subsequent processing. If restoration is impossible, the clip is replaced with a new one. Restoring the size of the clip by crimping is not allowed.