4-6. SOLDERING OF WINDINGS, COLLECTORS, BANDAGES
Connecting conductors by soldering is done using solder. According to the melting temperature, solders are divided into soft (tin - lead) with a melting point of up to 230 ° C and hard (copper - silver) with a melting point of 700 ° C and above. There is also an intermediate group of solders. Among the soft tin-lead solders, solders of the POS-30-POS-90 brands are used (the number indicates the percentage of tin) with a melting point of 180 ° C. Good results are obtained by soldering with pure tin (melting point 230 ° C). However, due to the scarcity of this metal, soldering with pure tin is carried out only in especially
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For anchor |
For anchor |
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in critical electrical machines in the presence of elevated temperatures.
Cadmium-zinc-silver solders (PKDTs Sr 31) with a melting point of 250 ° C are used for soldering the bandages of machines with class H insulation, and lead-silver solders (PSSr 2.5) with a melting point of 280 ° C are used for soldering the collectors of these cars
Among the hard ones, silver solders are used (P Av 45-70) with a melting temperature of 660-730 ° C and copper-phosphorus (PMF7, MF-3) with a melting temperature of 710-850 ° C. There are a number of requirements for solders: they must in molten form, penetrate well enough into the cracks between the surfaces being soldered, i.e., have sufficient fluidity, should not soften at temperatures as close as possible to the melting temperature, and provide sufficient mechanical strength of the solder at these temperatures. The soldering area should not be fragile. Soldering must have a sufficiently low electrical resistance and, in addition, over time, this resistance, as well as mechanical properties, should not deteriorate due to oxidation and aging.
It should be noted that solders with a high lead content are more prone to oxidation, and copper-phosphorus solders produce slightly more brittle compounds than silver ones.
In order for solder to provide a strong connection to the surfaces, in addition to their cleanliness, it is necessary that there is no film of oxides on them. At soldering temperature, the surfaces of any metal are covered with such a film. Fluxes are used to destroy the oxide film: rosin for soft rations and borax for hard ones. Pickling of soldered surfaces with acid when soldering live parts in electrical machines is not allowed, since acid destroys insulating materials.
Rosin can be used in solid form or in the form of an alcohol solution. Borax is used in the form of a powder or an aqueous solution. Soldering is done with a hot lamp or soldering iron. To speed up soldering, it is advisable to use electric soldering irons. For hard soldering, electrically heated pliers (Fig. 4-20) and graphite jaws are used,
Soft solders are used to solder collectors and bandages of all machines, stator and rotor busbars and connections for machines insulated according to class A with low operating temperatures.
It is recommended to use pure tin solder for soldering commutators and bandages of critical machines where significant overloads are possible. For normal machines, soldering of collectors and bands can be done with POS-30-POS-60 solder with 30-6E% tin content (GOST 1499-42).
Rice. 4-20. Welding pliers.
Hard solder is used to solder: tires (rods) of windings of machines that have high overheating and are insulated by class B-N, non-insulated windings of squirrel-cage rotors, damper cages, etc. Hard solder is also used to connect copper bars during the winding process of coils. Thin wires To avoid burnout, solder with soft solders.
Soldering technology soft solders involves the following operations: 1) cleaning the surface of the soldering area; 2) heating the soldering site to a temperature at which the solder melts upon touching the soldering site; 3) generous application of rosin; 4) introducing a stick of solder by pressing it against the gap between the surfaces to be soldered; 5) removing (with a rag) excess solder while hot; 6) cooling and washing off the remaining rosin with alcohol.
For better connection Soldered surfaces are recommended to be pre-tinned.
Soldering of collectors It is done in an inclined position so that the tin does not flow behind the cockerels. Warming up the collector blowtorch must be done very carefully so as not to let go of the plates. The winding is covered with asbestos fabric or
cardboard. For small collectors, it is enough to warm up the cockerels with a soldering iron.
The same applies to soldering wires into tape cockerels (Fig. 4-21). The slot in the plate, the cock and the end of the winding wire must be pre-tinned.
The best results are obtained by soldering the collectors in a bath. In this case, the anchor is installed vertically with the collector down. The end part of the cockerels is placed on an asbestos gasket lying on the side of a steel ring. The ring and the collector are heated using electric heating to a temperature of 250 ° C, after which the cockerels are generously coated with rosin and molten tin or solder is poured into the groove between them and the side of the ring.
This soldering method ensures good penetration of tin into all areas to be soldered.
Tin, naturally, should not be poured above the level of the cockerels so that it does not flow into the winding.
To perform soldering using this method, the repair shop must have a heating installation and a set of replacement rings for different diameters collectors.
A very convenient method (especially in repair conditions) is the method of heating the cockerels when soldering collectors, according to which the collector is covered with a copper clamp or wire, providing good contact with plates. One end from the welding transformer is connected to this clamp, and the other end is connected to a soldering iron, which is a copper rod with a graphite plate mounted in a handle made of insulating material. By touching the graphite pad to the cockerel, it is heated to the desired temperature.
Rice. 4-21. Soldering cockerels.
Soldering Shin double-layer winding involves preparation, i.e., covering the busbars with a staple and wedging them with a copper wedge (Fig. 4-22). The rotor is given a slight tilt to prevent tin from flowing into the winding.
If the tires have a large cross-section and the bracket is long, then to facilitate soldering of the entire surface, slots are made in the bracket or round holes(Fig. 4-"23). Soldering can only be done well
Rice. 4-22. Preparation
rotor rods
windings for soldering.
Figure 4-23. Bracket with holes.
only in the case that there are no voids left inside the bracket with wedged tires. Otherwise, the solder will leak out and the soldering will be weak.
Soldering bandages after winding them consists of uniform soldering thin layer tin of adjacent turns of bandage wire, so that a continuous belt is formed. In this case, there should be no places where the tin is applied in such a thick layer that it covers the turns of the bandage wire.
Soldering wires hard solder is produced in the following sequence: 1) preparation of the ends; 2) heating until dark red-crimson; 3) sprinkling with borax until the ends of the wire are completely covered with a layer of molten borax; 4) further heating until the solder melts, after which it is necessary to stop heating; 5) inspection and filing of the soldering area; checking its bending strength. Solder in the form of a leaf is placed between the ends of the wire. For large-section rectangular copper, the joint is made obliquely (angle 65°). The ends are placed in clamps and one is secured tightly, the other loosely. The soldering area is heated with a blowtorch, autogenous torch or electric tongs (Fig. 4-20).
Soldering tires can be produced using similar pliers with carbon jaws. Solder in the form of a leaf is placed under the bracket, which is compressed with pliers. The current is turned on for the short time required to melt the solder.
Good results are obtained by soldering with MF-3 phosphorous copper solder (melting point 720-740° C).
The surfaces to be soldered are cleaned with sandpaper and pressed with electric pliers. By turning on the current, the soldering area is heated to 750-800 ° C, and at the same time the edges of the surfaces to be soldered are coated with solder. Due to the high fluidity of this solder, it is distributed over the entire surface. For better spreading of solder, it is advisable to position the junction plane obliquely or vertically.
Soldering aluminum wires and busbars complicated by the fact that aluminum is highly susceptible to oxidation. Special solders have been developed for soldering aluminum wires with each other and with copper wires [L. 1] with a melting point of 160-450 ° C, containing mainly zinc, tin and additives: aluminum, copper, silver, cadmium.
Aluminum can be soldered with tin using an ultrasonic soldering iron. Such a soldering iron has, in addition to the heater, a winding powered by a current with a frequency of 20,000 Hz, covering a steel core made of a special alloy. At the same time, the working end of the soldering iron makes high-frequency oscillations that destroy the oxide strips.
At current repairs electrical machines perform following works: checking the degree of heating of the housing and bearings, the uniformity of the air gap between the stator and the rotor, the absence of abnormal noise in the operation of the electric motor; cleaning and blowing the electric motor without disassembling it, tightening the contact connections at the terminal boards and connecting the wires, cleaning the rings and collectors, adjusting and fastening the traverse brush holder, restoration of insulation at the output ends, changing electric brushes; changing and adding oil to the bearings. If necessary, carry out: complete disassembly of the electric motor with elimination of damage to individual places of the winding without replacing it; washing of components and parts of the electric motor; replacing faulty slot wedges and insulating bushings, washing, impregnating and drying the electric motor winding, coating the winding with topcoat varnish, checking the fan mounting and repairing it, grooving the rotor shaft journals and repairing the squirrel cage (if necessary), changing flange gaskets; replacing worn-out rolling bearings; washing plain bearings and, if necessary, refilling them; if necessary, welding and grooving of electric motor covers, partial soldering of cockerels; grooving and grinding of rings; repair of the brush mechanism and commutator; flow of the collector and its maintenance; assembly and testing of electric motor operation Idling and under load.
At major renovation carry out the following work: complete or partial replacement of the winding; straightening, wiping journals or replacing the rotor shaft; rebuilding rings or manifold; rotor balancing; replacement of fan and flanges; complete soldering of cockerels; cleaning, assembling and painting the electric motor and testing it under load.
Determining the condition of parts and assigning the type of repair. Defects are carried out before disassembly, during disassembly and after disassembly. Defective operations performed before disassembly: external inspection; familiarization with defects in the documentation; pre-repair tests at idle speed, if possible.
Before connecting to the network, check the condition of the shaft, bearing shields, bearings, the absence of the rotor touching the stator, the presence of lubrication, and the integrity of the phases; condition of the output ends and terminal board; winding insulation resistance.
If the test results are satisfactory, turn on the electric motor for 30 minutes under voltage, measure the no-load current in phases, check the noise of the electric motor, the operation of the commutator, the heating of the bearings, the amount of vibration, etc.
The inspection and inspection operations carried out during the disassembly process include: measuring the size of the air gaps between the iron of the stator and the rotor (armature) at four points spaced 90° from each other; measurement of shaft run-up in plain bearings; determination of clearances in sliding and rolling bearings; identifying faults in other parts.
During the disassembly process, damage or breakage of the disassembled individual units and parts or parts of electrical machines must not be allowed. Parts interconnected with tension are removed with universal pullers. The working and seating surfaces of components and parts of disassembled electrical machines are protected from damage.
Removed usable hardware, spring rings, dowels and others small parts stored for reuse. Disassembled components and parts are placed in technological containers or on racks. The disassembler's workplace is equipped with a table or workbench and special tools and devices. A device for removing bearings from the rotor shaft is placed near the dismantler's workplace. When disassembling electric motors, you can use a special stand for legs. The stand, equipped with a lift, a rotary table and a conveyor (plate, trolley, etc.), ensures complete disassembly of electric motors with a rotation axis height of more than 100 mm. To lift assembled products, components and parts whose weight exceeds 20 kg, you should use a lifting -transport mechanisms and devices. Grasping components and parts by working surfaces is not allowed. Lifting and transport equipment must have a smooth lifting and lowering speed, and the load capacity must be at least 1 ton.
The devices used to remove bearings from the rotor shaft and to remove the rotor from the stator bore must ensure the protection of the working surfaces from damage.
The tool used during disassembly must not have nicks, burrs or other defects on work surface and comply with safety requirements. The production container must contain all disassembled components and parts and comply with the requirements of industrial sanitation. The technological process of disassembly consists of the following operations: preparatory, direct disassembly and control. The choice of disassembly method depends on the technical and organizational capabilities of production. Operations of the technological process produced in a room with a temperature of 20 ± 5 ° C and a relative humidity of no more than 80%. During preparatory operations, place the container with electric motors on the stand, and the electric motor on the disassembler’s table or transfer trolley of the disassembly stand. For closed motors, unscrew the bolts securing the external fan casing and remove it; unscrew the fasteners securing the fan and remove it; in the case of fastening the fan with a spring ring, first remove it with a special tool. For motors with a wound rotor: disconnect the connecting wires, release the fastenings, remove the cover of the slip rings, remove the brushes; in case of repair of the rotor windings, unsolder the connecting clamps from the output ends; remove the tap holder and remove the slip rings from the rotor shaft.
For electric motors, the design of which provides for the location of the slip ring assembly inside the bearing shield, removal of the slip rings is carried out after removing the bearing covers (outer and inner), the bearing shield and the bearing on the side opposite the working end of the shaft.
For crane and metallurgical electric motors, inspection hatch covers are also removed; detach the capsules from the bearing shields and remove the outer sealing rings; drain the oil from the oil chambers (at the plain bearings).
Unscrew the bolts securing the outer bearing caps and remove the latter. If there are spring rings between the bearing cap and the bearing, the latter must be preserved. Remove the spring ring securing the bearing (if equipped). Unscrew the fasteners securing the bearing shields, the cover and the terminal block (block), and remove the latter. The seals provided by the design in the terminal box are retained. When dismantling electric motors at the disassembler's workplace, preparatory operations are carried out here.
The front (from the side of the working end of the shaft) bearing shield is removed from the sharpening of the frame using a lever inserted into the gap between the ears of the bearing shield and the frame, or release bolts. Squeezing should be done evenly until the shield completely comes out of the centering sharpening.
It is allowed to remove the bearing shield from sharpening the frame using light blows of a hammer on a soft metal drift or a pneumatic hammer on the ends of the ears of the bearing shield.
When removing the front bearing shield from sharpening, it is necessary to support the shaft manually or with linings, preventing the rotor from hitting the stator. The bearing shield is removed from the shaft by turning it on the bearing, avoiding distortions. Rear (on the side opposite the working end of the shaft) bearing shield removed in the same way as the front one. You can remove the rear bearing shield after removing the rotor from the stator. The rotor is removed using a special device, while preventing the rotor from touching the bore and the stator winding.
Tags with repair numbers are attached to the stator, rotor and bearing shields. The disassembled units and parts are placed in production containers or on racks and transferred to the subsequent operation.
When disassembling at a disassembly stand, the electric motor is installed on a transfer cart, and it is sent along the conveyor using a pusher clamp. Preliminary disassembly operations are performed and the trolley is transferred to the hydraulic stand table.
Install the electric motor so that the centers of the hydraulic cylinder rods of the installation coincide with the centers of the shaft of the electric motor being disassembled, and clamp the electric motor shaft in the centers. Lower the table down and push the cart onto the conveyor.
Raise the table until the electric motor is completely seated on it, and clamp the legs of the electric motor with clamps.
Move the left cylinder rod to the right until the bearing shield completely exits the stator grinding. Remove the bearing shield from the bearing. Install a stop between the bearing and the motor housing. By moving the right cylinder rod to the left, the right bearing is pressed out from the rotor shaft. Do the same with the left bearing shield and bearing. The centers are released and the cylinder rods of the hydraulic stand are moved away from the rotor shaft of the electric motor. Rotate the table with the electric motor 60-90° and remove the bearings and internal bearing caps. Remove the rotor from the stator bore using a special device, while preventing the rotor from touching the bore and stator winding.
Permissible radial clearances in plain bearings of electrical machines. Table 3.14.
| Shaft diameter, mm | Permissible clearances mm, at rotation speed, rpm | |||
| 750-1000 | 1000-1500 | 1500-3000 | ||
| 18-30 | 0,04-0,093 | 0,06-0,13 | 0,14-0,28 | |
| 30-50 | 0,05-0,112 | 0,075-0,16 | 0,17-0,34 | |
| 50-80 | 0,065-0,135 | 0,095-0,195 | 0,2-0,4 | |
| 80-120 | 0,08-0,16 | 0,12-0,235 | 0,23-0,46 |
Notes:
l. During operation, double the maximum clearances are allowed.
2. In the absence of special instructions from the manufacturer, the gap between the shaft journal and the upper liner should be specified within the following limits; for bearings with ring lubrication (0.08÷0.10) Dsh, for bearings with forced lubrication (0.05÷0.08) Dsh, where Dsh is the diameter of the shaft journal.
3.To create more favorable conditions formation of an oil wedge, it is recommended to make lateral clearances B = a for split bearings. In this case, the bearings are bored to a diameter of D + 2a using spacers of thickness a.
The permissible difference in air gaps of electrical machines should not exceed the values specified in the factory instructions, and if such data is not available, then the gaps should differ by no more than that indicated below for machines: asynchronous - by 10%; synchronous low-speed ones – by 10%; synchronous high-speed – by 5%; DC with loop winding and a gap under the main poles of more than 3 mm -5%; DC with a wave winding and a gap under the main poles of more than
1 mm – by 10%; as well as an armature and additional poles - by 5%.
The run-up - the axial movement of the machine shaft in the plain bearings in one direction from the central position of the rotor should not exceed 0.5 mm for machines with voltages up to 10 kW, 0.75 mm - for machines 10-20 kW, 1.0 mm - for machines 30 -70 kW, 1.5 mm – for machines 70-100 kW. The total bilateral shaft spread should not exceed 2-3 mm.
Clearances in rolling bearings. Table 3.15.
Inspection and inspection operations after disassembling electric machines include: external inspection and measurement of all wear surfaces of parts; final conclusion on the condition of parts as a result of inspection, checks and tests. The results of defect detection are recorded in a repair card, on the basis of which the technologist or foreman fills out transaction card and prescribes the type of repair. Defective parts and assemblies are repaired using the methods indicated below.
Technology for repairing components and parts of electrical machines. Collector design. For most electrical machines, the collector design shown in (Fig. 3.27, and where, 1 – steel body; 2 – insulation; 3 – cockerels; 4 – collector plate; 5 – conical tension washer; 6 – locking screw; 7 – gasket micanite).
The machine collector must be cleaned of dirt and grease. The collector insulation must be reinforced, and the edges of the collector plates must be chamfered. A collector with unevenness up to 0.2 mm must be polished, 0.2-0.5 mm must be ground, and more than 0.5 mm must be machined. The collector runout of machines (checked using an indicator) should not exceed 0.02 mm for collectors with a diameter of up to 250 mm and 0.03-0.04 mm for collectors with a diameter of 300-600 mm.
Repair of collectors. Information about possible malfunctions, the reasons for their occurrence and methods for repairing collectors (Fig. 3.27, b) are given in table. 69.
Rice. 3.27. Manifold structure. (a) Molding of the manifold on lathe(b)
Repair of slip rings. The set of slip rings is shown in (Fig. 3.28. where, 1 – bushing; 2 – electrical cardboard; 3 – contact ring; 4 – insulation of studs; 5 – contact studs (leads from rings))
Minor damage to the surface of the contact rings (burns, runout, uneven wear) can be eliminated by cleaning and polishing without dismantling the rings. In case of major damage to the surfaces, the rings are removed and ground, reducing their thickness by no more than 20%.
A breakdown of the insulation on the body, as well as extreme wear of the rings, necessitate their replacement. It is advisable to make replacements only in large electrical centers, where for each type of slip rings a standard technological process of disassembly, manufacturing, assembly and testing is carried out with the provision of appropriate devices and equipment.
Core repair. The cores (active steel) simultaneously serve as a magnetic core and a frame for placing and strengthening the winding. When repairing and replacing the winding, it is necessary to check the cores and eliminate any detected defects. The main malfunctions of the stator and rotor cores, their causes, as well as solutions are given in 3.16.
Collector faults. Table 3.16.
| Malfunction | Cause | Repair |
| Surface burning | Sparking. All-round fire | Turning, grinding |
| Beating. Plate protrusion | Poor build. Poor quality micanite | Heat. Pull-up. Turning |
| Insulation protrusion between plates | Wear of plates. Collector weakening | Promotion. Tightening. Turning |
| Protrusion of plates at the edge of the collector | Extreme turning. Plates too thin | Replacing a set of plates and inter-lamella insulation |
| Part of the cockerels is broken off (in the slot) | Careless knocking out of winding ends from the slot | Disassembly. Repair or replacement of plates |
| Short circuit between plates | Burrs on the surface. Burnout of micanite insulation due to ingress of oil and copper-coal dust Short circuit inside the collector | Inspection. Clearing. Deep cleaning between the plates. Washing with alcohol. Covering with paste |
| Short to body | Breakdown, burnout of insulating cones | Disassembling, repairing or replacing a manifold with a molded one on a machine (Fig. 3.27) |
Malfunctions of the stator and rotor cores. Table 3.17.
| Malfunction | Cause | Repair |
| Loosening the pressing | Loss of ventilation struts. Loosening of tie bolts. Breaking off and falling out of individual teeth | Repair the spacers. Tighten the bolts. Hammer and strengthen the wedges |
| Fluffing of teeth | Weak end sheets or pressure washers | Pre-pressing. Force of outer sheets |
| Core heating | Burrs. Sanded areas. Mechanical damage to the surface of the cores. Damage to the insulation of the coupling bolts | Clearing |
| Burnout of areas | Breakdown of winding insulation on steel | Replacement of insulation. Clearing. Re-lamping |
| Steel deformation | Incorrect assembly or installation of the machine. Mechanical damage | Edit |
Fig.3.28. Contact rings assembled.
Conditions for sparkless switching. If the current density per unit surface of contact of the brush with the commutator in any place becomes too large, the brushes spark. Sparking destroys the brushes and commutator surface. Reliable contact between the brush and the commutator is ensured by a smooth mirror surface of the commutator (without protrusions, dents, burns, without eccentricity or runout).
The brush lifting mechanism must be in good working order. Brushes cannot be used on one machine different brands. They must be installed strictly in neutral. The distance between the brushes around the circumference of the commutator must be equal. Deviations in the distances between the running ends of the brushes should not exceed
% for machines with power up to 100 kW. The distance from the holder to the surface of the collector should be 2-4 mm. When the brushes are inclined, the acute angle of the brush should be approaching.
Permissible deviations of the brush holder clips from the nominal size in the axial direction are 0-0.15 mm; in the tangential direction, with brush widths less than 16 mm -0-0.12 mm; with a brush width of more than 16 mm – 0-0.14 mm.
Permissible deviations of brush sizes from the nominal dimensions of the brush holder cage can only be with a minus sign. Permissible deviation values: in the axial direction from –0.2 to –0.35 mm; in the tangential direction (with brush widths up to 16 mm) from –0.08 to –0.18 mm; in the tangential direction (with brush widths of more than 15 mm) from –0.17 to –0.21 mm.
The clearance of the brushes in the cage should not exceed –0.2 ÷ 0.5 mm in the axial direction; in the tangential direction (with brush widths up to 16 mm) 0.06 ÷ 0.3 mm; in the tangential direction (with brush widths more than 16 mm) 0.07 ÷ –0.35 mm. The working (contact) surface of the brushes must be ground to mirror shine. The specific pressure of different brands of brushes should be in the range of 0.15-4 MN/m2 and accepted according to catalogs.
Fig.3.29. Shapes of electric machine shafts: a) direct current machines; b), c) asynchronous motors.
The deviation in the value of the specific pressure between individual brushes of one rod is allowed by ±10%. For engines subject to shocks and shocks (crane engines, etc.), the specific pressure can be increased by 50-75% compared to the catalog data.
Repair of mechanical parts. Shaft repair. The shapes of electric machine shafts, indicating fits and roughness, are shown in Fig. 20.9. The shaft may have the following damage: bending, cracks, scuffs and scratches of the journals, general wear, taper and ovality of the journals, camber of key grooves, nicks and riveting of the ends, crumpling and wear of the threads at the ends of the shaft, loss of tension in the fit on the core shaft and, in rare cases, breakage shaft
Repairing shafts is a responsible job and has specific features, since the shaft being repaired is very difficult to separate from the core associated with it. The permissible rate for turning the shaft journals is 5-6% of its diameter; permissible taper 0.003, ovality 0.002 of the diameter. Shafts that have cracks with a depth of more than 10-15% of the diameter and more than 10% of the shaft length or perimeter must be replaced. The total number of dents and indentations should not exceed 10% of the seating surface for the pulley or coupling and 4% for the bearing.
Repair of frames and bearing shields. Main damage to frames and bearing shields: breakage of frame mounting feet; damage to the threads in the holes of the frame; cracks and warping of bearing shields; wear of the seating surface of the shield hole for the bearing seat.
Repair of the frame and bearing shields consists of welding cracks, welding broken legs, restoring worn seats, damaged threads in holes and removing the remaining torn bolt rods. The runout of the centering sharpening relative to the axis is radial and no more than 0.05% of the sharpening diameter.
Repair of plain bearings. Damage to sliding bearings: wear along the inner diameter and ends, cracking, chipping, sagging, melting of the fill, tightening of the grooves, wear of the bushing along the outer diameter. Wear on the inside diameter and ends is the most common damage.
The service life (in years) of plain bearings filled with B16 babbitt, depending on the operating mode, is as follows: Light 4-5; Heavy 1.5-2; Normal 2-3; Very heavy 1-1.5
The temperatures for heating the bearings before pouring and melting the babbitts are given in Table. 71. Repair of sliding bearings consists of the following operations: melting the old casting, repairing the liner, preparing it and the alloy for casting, pouring and cooling.
Centrifugal filling of bearings is carried out on a lathe using a special device (Fig. 3.28, where, 1 – faceplate; 2 – tie rod; 3 – liner; 4 – babbitt filling boundary; 5 – funnel; b – bucket with babbitt). The rotation speed of the chuck is set according to the table. 72 depending on bearing size. The processing allowance is 2-2.5 mm per side with an internal diameter of up to 150 mm. The allowance at the ends is 2-4 mm. Oil distribution and oil catching grooves for bearings with a shaft journal diameter of 50-150 mm are made 3-6 mm wide and 1.5-3 mm deep.
Table 3.18.
* The numerator indicates the temperature of the beginning of melting, the denominator indicates the end of melting.
Fig.3.28. Filling the liner centrifugally
Basic requirements for the installation of sliding bearings: the working parts of the bearing shells must be fitted (by scraping along the shaft journals in their middle part along an arc from 60 to 120°); the standard contact surface (when checking for paint) of the shaft journal and the lower bearing is two spots on 1 cm 2 surfaces on an arc of 60-90°; the presence of dense belts at the ends of the shaft journal and the upper liner - one spot per 1 cm 2. Damage and replacement of rolling bearings. The main damage to rolling bearings is wear of the working surfaces of the cage, cage, ring, balls or rollers, as well as the presence of deep marks and scratches, traces of corrosion, and the appearance of discoloration. Rolling bearings are not repaired at ERC, but replaced with new ones. For medium-power electric machines, the service life of rolling bearings is 2-5 years, depending on the size of the motor and its operating mode.
Rotation frequency of the cartridge when filling bearings. Table 3.19.
| Chuck rotation speed, rpm | Inner diameter of bearings, mm | Chuck rotation speed, rpm | |||
| B16, BN | B83 | B16, BN | B83 | ||
Basic requirements for installing rolling bearings: the inner rings of the bearings must be seated tightly on the shaft; the outer rings of the bearings must be inserted into the bores of the bearing shields freely with a gap of 0.05-0.1 mm in diameter; axial clearance (the amount of axial movement of one race relative to other) should not exceed 0.3 mm.
Seal repair. Grease leakage from bearings into electrical machines occurs due to design flaws, improper installation of seals and improper application of lubricant. A ring with teeth, mounted on the shaft in addition to the usual stuffing box seal, prevents lubricant from getting inside the machine. To install such a ring, it is necessary to shorten the bearing shell of the ring lubricant.
To prevent severe leakage of lubricant into the machine, an oil slinger ring with inclined reflectors is mounted on the shaft, throwing oil into the bearing. If axial ventilation is strong, additional labyrinth type seals should be installed. Repair of sealing devices consists of replacing studs with damaged threads, drilling and tapping new holes in the sealing rings.
Rotor balancing. To ensure the operation of the electric machine without beating and vibration after repair, the rotor assembly with all rotating parts (fan, rings, coupling, pulley, etc.) is subjected to balancing.
There are static and dynamic balancing. The first is recommended for machines with a rotation speed of up to 1000 rpm and a short rotor, the second, in addition to the first, for machines with a rotation speed of more than 1000 rpm and for special machines with an extended rotor. Static balancing is carried out on two prismatic rulers, precisely aligned horizontally. A well-balanced rotor remains motionless in any position relative to its horizontal axis. The rotor balancing is checked for 6-8 rotor positions, turning it around its axis at an angle of 45-60°. Lead weights are driven into special dovetail-shaped grooves. During dynamic balancing, the location of the weight is determined by the amount of beating (vibration) when the rotor rotates. Dynamic balancing is carried out on a special balancing machine (Fig. 3.29, where 1 – stand; 2 – balanced rotor; 3 – pointer indicator; 4 – coupling; 5 – drive). A rotating rotor (armature) installed for testing, when unbalanced, begins to vibrate along with the bearings.
Rice. 3.29. Machine for dynamic balancing of rotors:
secured by welding or screws.
To determine the location of imbalance, one of the bearings is fixed motionless, then the second continues to vibrate during rotation. The tip of a colored pencil or an indicator needle is brought to the rotor, which leaves a mark on it at the point of greatest deflection of the rotor. When the rotor rotates in the opposite direction at the same speed, a second mark is applied in the same way. Based on the average position between the two marks obtained, the location of the greatest imbalance of the rotor is determined.
At the point diametrically opposite to the point of greatest imbalance, a balancing weight is secured or a hole is drilled at the point of greatest imbalance. After this, the imbalance of the second side of the rotor is determined in a similar way.
The balanced machine is installed on a smooth horizontal plate. If the machine is satisfactorily balanced, operating at rated speed, there should be no rocking or movement on the plate. The check is carried out at idle speed in engine mode.
Technology for repairing electrical machine windings. Determining the scope of repairs. Before repairing the windings, it is necessary to accurately determine the nature of the fault. Serviceable electric motors that operate abnormally as a result of damage to the supply network, drive mechanism, or incorrect marking of the terminals are often sent for repair.
The basis of the armature winding of DC machines is a section, that is, a part of the winding enclosed between two collector plates. Several winding sections are usually combined into a coil, which is placed in the grooves of the core.
The circuits of single-phase windings are constructed basically according to the same rules as the circuits of three-phase windings, only in them the working phase occupies 2/3 of the slots, and the starting phase occupies 1/3. For capacitor motors, half of the slots are occupied by the main phase and half by the auxiliary phase.
When scheduling repairs, you should remember that for electric motors with a power of up to 5 kW with a double-layer winding, if it is necessary to replace at least one coil, it is more profitable to rewind the stator completely. For motors with a power of 10-100 kW with round wire winding, one or two coils can be replaced by the pulling method without lifting undamaged coils.
Connections of the output ends of the windings of AC and DC electrical machines. The windings of three-phase alternating current machines can be connected in a star or triangle. The ends of the windings are connected either tightly inside the machine or outside on the clamp board. With an external connection, six ends of three windings are brought out to the terminal board (Fig. 3.30 a, b) where, a - a synchronous or asynchronous machine with six terminals (the windings are connected in a star "DU"), b - a synchronous or asynchronous machine with six terminals (windings connected in a triangle), with an internal blind connection - three ends of three windings for connecting an external network (Fig. 197, c, d) where, c - synchronous or asynchronous machine with three terminals (windings connected in a star), d - synchronous or asynchronous machines with three terminals (windings connected in a triangle)
Fig.3.30. Connection diagrams for winding terminals of three-phase alternating current machines.
Designations of winding terminals. Table 3. 20.
Designations of the terminals of the windings of DC machines. Table 3.21.
Figure 3.31 (a) shows the terminal diagram of the windings of DC machines. The terminals of the armature winding Y2 and the winding of additional poles D1 are connected inside the machine. D2 is also displayed on the terminal board. In some cases, the winding of additional poles consists of two halves and is connected on both sides of the armature (Fig. 3.31, where, b - with the location of parts of the winding of additional poles on both sides of the armature.) Here both ends of the winding of additional poles D1 and D 2.
Fig.3.31. Terminal diagrams for DC machine windings
Repair of stator windings of electrical machines. To record winding data during rewinding, use the following form of winding card.
Wrapping card
Motor type
Factory number
Date of manufacture
power, kWt
Voltage, V
Number of phases
Rotation speed, rpm
frequency Hz
Phase connection
Stator package length, mm
Stator bore diameter, mm
Number of grooves
Type of winding (double-layer, single-layer concentric, chain, single-layer concentric in bulk, etc.)
Winding diagram
Shape of the frontal parts (for two-plane and three-plane single-layer windings)
Overhang of the frontal parts (distance from the end of the package to the most distant point of the frontal parts of the winding): from the circuit side, mm from the opposite side, mm
Number of wires in the groove: in the upper layer, in the lower layer, total.
Number of parallel wires
Winding wire: brand, diameter, mm
Winding pitch (for a concentric winding, indicate the pitches of all coils of a coil group or semi-group)
Number of parallel branches
Average coil length, mm
Sketch of the groove with dimensions, insulation and wire arrangement
Dimensions, shape and material of groove wedges
Wrapper:
The technological process for manufacturing a stator winding for an asynchronous machine being repaired consists of the main stages given in Table. 73. A device for cleaning the grooves for laying coils, a tilter, and soldering the insulation of stator winding connections are shown in (Fig. 3.32 (a) where, 1–holder; 2–reference; 3–mandrel; 4–rotor; 5–screw; 6–stand Repair of rotor windings The sequence of operations for repairing rotor windings is given in Table 3.22.
Fig.3.32. (a) - a device for cleaning the grooves, (b) - placing loose winding coils in the grooves.
Technological process of rewinding the stator of an asynchronous motor. Table 3.22.
| Operation | Repair work | |
| Removing the stator winding | The frontal parts of the coils and connecting wires are freed from fastening after annealing the stator; cut connections between coils and phases; push the wedges down and knock them out of the stator grooves; remove the winding from the slots; clean the grooves, blow and wipe | Devices for mounting stator windings and cleaning slots |
| Preparation of insulation and sleeves for electric motor stator slots | Install the stator on the tilter, measure the length and width of the groove; a template is made, pressed liners, belts and other insulating material are cut; install sleeves and lay belts | Stator contactor |
| Winding the stator coils on winding machine | Unpack the coil, measure the wires, install the coil on the turntable; secure the wires in the leash; determine the size of the coil turn. Set up a template; wind the coil group, cut off the wire, tie the wound coil in two places and remove it from the template | Micrometer. Universal template. Winding machine |
| Laying coils in the stator | Place the coils in the stator slots. Install gaskets between the coils in the grooves and frontal parts. The wires are sealed in the grooves and the frontal parts are straightened; secure the coils in the grooves with wedges, insulate the ends of the coils with lacquer cloth and keeper tape. | Wrapper tool. Glue jar |
| Assembling the stator winding circuit | Clean the ends of the coils and connect them according to the diagram; electrically weld (solder) the joints, prepare and connect the lead ends; isolate joints; bandage the connection diagram and straighten frontal overhangs; check the correct connections and insulation. | File, knife, pliers, hammer. electric arc soldering iron, megaohmmeter, test lamp |
| Drying and impregnation of the stator winding (rotor, armature) with varnish | Load the stator (rotor, armature) into the drying chamber using a lifting mechanism; unloaded from the chamber after drying the winding; impregnate the stator winding in a bath, allow it to drain after impregnation, and load it back into the chamber; dried; remove from the chamber and remove varnish stains from the active part of the magnetic circuit with a solvent | Drying chamber |
| Coating the frontal parts of the winding with electric enamel | Cover the frontal parts of the stator winding (rotor, armature) with electric enamel | Brush or spray |
Sequence of operations for repairing a rod rotor. Table 3.23.
| Operation | Repair work | Equipment, tools, fixtures |
| Dismantling the rod rotor winding circuit | Install the rotor on the trestle, clean it from dust and dirt, using gas burner unsolder the bandages and remove them, unsolder the circuit and remove the lead ends | Transport device |
| Removing rods from grooves | Remove the rods from the rotor grooves using a device, clean the grooves and winding holders from old insulation | Dismantling device |
| Tire cleaning and straightening | Clean the tires from old insulation, straighten, strip and tin the ends of the tires | File |
| Isolated | Apply insulation to tires | Brush |
| Preparation of insulation and installation of sleeves | They make gaskets (in the rotor grooves and spacers), insulation for the winding encoder, under-banding and for busbar layers. Apply insulation to the winding holder, install gaskets in the grooves and straighten them using a mandrel | Scissors, wrapper tool |
| Laying the winding | The bottom layer of tires is placed in the grooves of the rotor, spacers are installed, the frontal parts are insulated, the top layer is placed in the grooves, the frontal parts are compressed with compression rings, spacers are installed and the grooves are jammed. | Template for control |
| Circuit assembly | Pull the output ends into the rotor shaft, put on the cockerels and install jumpers according to the diagram. The cockerels are wedged with copper wedges, the circuit is assembled and welded using electric welding (soldering). | File. Electric soldering iron Comb for knocking out wedges, special knife |
Repair of armature windings. The integrity of the armature winding can be checked using the voltage drop method, which makes it possible to detect interturn short circuits, breaks, poor-quality soldering, and incorrect connection of the windings to the collector. This method allows you to locate the coil connected to the armature body. To do this, one probe from the power source is connected to the shaft or package, and the second probe alternately touches the collector plates (Fig. 3.33:a) to determine the quality of soldering in the “cockerels” and determine damage in the windings; b) c) correct pole rotation in motors and generators). The minimum reading of the millivoltmeter will be when the probe comes into contact with the plates to which the coil, closed to the housing, is attached. For the same purposes, you can use the transformer method (Fig. 3.33, d). The sequence of operations for repairing armature windings is given in Table. 75. Repair of pole coils. The sequence of operations for rewinding the windings of pole coils is given in Table 3.24.
Fig.3.33. Schemes for testing DC electrical machines.
a) - the quality of rations in the “cockerels” and the determination of damage in the windings; b, c – the correctness of the alternation of poles in motors and generators; d) - diagram of the location of the groove with short-circuited turns: Фu1 magnetic flux created by the current of the pulse generator; Fi2 is the magnetic flux from the current flowing through short-circuited turns.
Technological process of anchor repair. Table 3.24.
| Operation | Repair work | |
| Connecting the winding from the collector | Wedges are made and installed between the cockerels, the cockerels are soldered, the ends of the winding are raised, and excess tin is removed. | Electric arc soldering iron |
| Removing the old winding | The bandages are removed, the wedges are upset and knocked out of the grooves; remove the winding and clean the armature slots; measure and make insulation, lay it in the grooves of the armature | Wrapper tool |
| Making a new winding | Sections of the armature winding are wound on a machine, placed in the grooves, the frontal parts of the winding are insulated, wedges are made and installed in the grooves. | Winding template |
| Winding impregnation Banding | Impregnate the armature winding with varnish in a bath, dry it in a drying chamber (before and after impregnation); check the winding insulation on the housing, prepare and place the insulation under the bands; apply cord and wire bandages and seal the latter | Drying chamber. Hand scissors, combination nippers |
| Connecting the armature winding to the commutator | Straighten the collector cockerels, tin the cockerels and the ends of the winding, disassemble the ends according to the diagram and attach them to the cockerels, wedge the cockerels, solder and clean | Asbestos strips 0.3mm thick |
Rewinding to a different voltage and a different rotation speed of the stator windings of asynchronous motors. When converting windings to a different voltage, the number of effective conductors in the slot is changed in direct proportion to the phase voltage. If the number of parallel branches of the winding changes during rewinding, the resulting number of effective conductors must be multiplied by the ratio of the new number of parallel branches to the old number. If the old winding had three parallel branches, and the new one is made with two, then the multiplier will be equal to 2/3, if the old winding had 2 branches, and the new one is made with three, then the multiplier is 3/2. For ease of conversion at standard phase voltages of 220, 380, 500, 660 V use Fig. 3.34, a. The number of conductors along it is determined as follows: on the horizontal line of the old voltage, the old number of conductors is found and a vertical line is drawn from the found point until it intersects with the line of the new voltage. The intersection point gives a new number of conductors.
The process of rewinding the winding of pole coils. Table 3.25.
| Operation | Work carried out | Equipment, tool, fixture |
| Removing poles with coils | Remove the insulation, unsolder the connections between the coils, disconnect the winding terminals from the terminal panel and mark the poles; unfasten and remove the poles with the coils; remove the coils and insulating pads from the core | Electric soldering iron, pliers |
| Rewinding the winding of pole coils | Remove the insulation from the coil, unwind the coil, wind a new coil on the machine; impregnate the coil with varnish in a bath, dry it in a drying chamber, cover the outer surface with enamel by hand | Winding template drying chamber, spray bottle, varnish jar |
| Installation of poles with coils | Clean the output ends of the coils from varnish, install insulating gaskets and coils on the core. Install the gaskets and poles into the frame and secure; check the diametrical distances between the poles, solder and insulate the connections between the coils. Bring the ends to the terminal panel and check the polarity of the pole coils | Scale ruler, glue jar, megohmmeter |
Example. At a phase voltage of 220 V, the number of conductors in the slot is 25. Determine how many conductors there should be at phase voltages of 380, 500 and 660 V.
On the 220 V horizontal we find point 25, draw a vertical line down from it and find the number of conductors in the groove at other voltages: 43 – at 380 V; 57 – at 500 V and 75 – at 660 V.
When changing the number of parallel branches, the resulting number of effective conductors in the slot must be multiplied by the ratio of the new number of parallel branches to the old one. So, if the old number of branches is 3, and the new number of branches is 2, the result obtained in Fig. 3.34 should be multiplied by 2/3. The number of effective conductors in the stator slot varies in direct proportion to the voltage, and the wire cross-section is inversely proportional.
The new diameter of the copper wire, while maintaining the number of parallel branches and parallel conductors, is found as the product of the old diameter and the square root of the ratio of the old voltage to the new one. For the convenience of recalculating the diameter, Fig. 3.34, b is shown.
Fig.3.34. Determining the number of conductors in the groove when rewinding to a different voltage.
Technological processes impregnation, drying and varnishing of windings . Impregnation of the windings is carried out in a special boiler filled with varnish, in which a pressure of up to 0.8 MPa is created and maintained for 5 minutes, then the pressure is reduced to normal and raised again for 5 minutes; this operation is repeated up to 5 times. Information about impregnating varnishes and recommended amounts of impregnation are given in table. 3.26. Drying of windings after impregnation with varnishes is divided into two stages. At the first stage (at 60-80°C) the solvent is removed. At the second stage, the varnish base hardens at a temperature of 120-130°C, depending on the varnish and the heat resistance class of the insulation. If the windings are subjected to re-impregnation, they are cooled in air to 60-70°C and then immersed in varnish again.
Impregnating varnishes and number of impregnations. Table 3.26.
| Type of winding | Recommended varnish | Number of impregnations |
| Loose windings of stators, armatures and rotors (impregnation in the assembly; wires PBD, PELBO, PELSHO): normal version; moisture-resistant version | BT-988 321T BT-987 321T | 3-5 3-5 |
| Template windings of armatures, stators and rotors (impregnation of turn insulation): normal and moisture-resistant version (PBD wire) | BT-988 | |
| Impregnation of body insulation of template windings: normal version (wires PBD, HDPE) moisture-resistant version (wire PSD) | BT-988 BT-987 | |
| Impregnation of wound stators with template winding: normal version (wires PBD, HDPE) moisture-resistant version (wires PBD, HDPE) | BT-988 BT-987 | |
| Impregnation of wound rotors with rod winding: normal version, moisture-resistant version | 321T 321T | |
| Impregnation of shunt coils of DC machines: normal version (wires PBD, PELBO, PEV-2) moisture-resistant version (wires PBD, PELBO, PEV-2) | BT-987 321T BT-987 321T | 2-3 |
Notes: 1. The impregnation method for shunt coils is under vacuum and pressure, for the rest - hot immersion. 2. Insulation class for normal and moisture-resistant versions – A
Varnishing of the windings is carried out immediately after drying the impregnated windings after they are laid in the grooves. The recommended winding temperature for varnishing is 50-60°C. The thickness of the varnish or enamel film is no more than 0.05-0.1 mm. Windings coated with air-drying varnish or enamel are cooled in air until the stickiness disappears (usually 12-18 hours). To reduce time varnish coating can be dried in an oven at 70-80°C for 3-4 hours. Cover varnishes and oven-drying enamels are dried at 100-180°C depending on the type of enamel and the heat resistance class of the insulation (Table 3.27).
Modes of varnishing and drying of windings. Table 3.27.
| Windings | Varnishing method | Type of topcoat or enamel | Drying temperature, °C | Drying time, h |
| Standard AC machine stators | Pulverization | BI-99, GF-92ХС, GF-92ХК | 15-25 | 6-24 |
| Anchors and rotors of normal design | » | BT-99, GF-92GS | 20; 80-110 | 4 or more |
| AC machine stators with moisture-proof insulation | Immersion Pulverization | BT-99, GF-92HS GF-92GS | 110-120 | 6-24 3-10 |
| Anchors and rotors with moisture-resistant insulation | Immersion Pulverization | 460, BT-99 GF-92GS | 120-140 110-120 | 8 and more 4-12 |
| AC machine stators with class H insulation | Immersion Spraying | PKE-15, PKE-13 PKE-19 or PKE-14 | 120-180 - | 8-12 – - |
During a major overhaul, as a rule, a complete replacement of the winding and insulation of the machine is performed. Windings made from round wire and multi-turn windings made from rectangular wire of small cross-section, as a rule, are not restored, but are made again. Windings made from large-section rectangular wire are reused, replacing the turn and body insulation. In all cases of winding repair, all insulation must be replaced. The round wire winding is laid manually, since the mechanization of the process is hampered by the low quality of the cores after removing the windings, a large range and small quantities of similar machines.
Malfunctions of electrical machines. Damage to electrical machines can be mechanical or electrical. Mechanical damage includes: melting of babbit in plain bearings; destruction of the separator, ring, ball or roller in rolling bearings; deformation of the rotor shaft (armature); formation of deep workings (paths) on the surface of collectors; weakening of the poles or stator core on the frame, pressing of the rotor core (armature); rupture or slipping of wire bands of rotors (anchors), etc.
Electrical damage is usually called: breakdown of insulation on the housing; breakage of conductors in the winding; short circuit between the turns of the winding; disruption of contacts and destruction of connections made by soldering or welding; It is unacceptable to reduce the insulation resistance due to its aging, destruction or moisture, etc.
The number of pre-repair operations for identifying malfunctions of electrical machines includes: measuring the insulation resistance of the windings (in order to determine the degree of moisture); testing the electrical strength of the insulation; checking the integrity of the bearings, the axial run of the rotor (armature), vibration, the correct fit (rubbing in) of the brushes to the commutator and slip rings while the machine is idling; determination of the gaps between the rotating and stationary parts of the electric machine, as well as monitoring the condition of fasteners, the tightness of the bearing shields on the sharpening points of the frame and the absence of damage (cracks, chips, etc.) in individual parts and parts of the machine.
Work on pre-repair identification of faults and damage to electrical machines is called defect detection.
Defects are carried out by external inspection and testing during partial or complete disassembly of the electrical machine.
However, such defect detection does not always make it possible to identify and accurately determine the nature and extent of its damage, and as a result, it is impossible to determine the volume of upcoming repair work. The most complete picture of the condition and required repairs of an electrical machine is provided by defect detection performed after disassembling it.
All malfunctions and damages discovered after disassembling the electrical machine are noted in the defect map and, on their basis, a repair route map is drawn up indicating the work to be performed for each repair unit or for individual parts of the machine being repaired.
The main repair work for electrical machines includes disassembly, repair of windings and mechanical parts, assembly and testing.
repaired cars.
Before repairs, carefully inspect the windings, paying special attention to where the windings exit the stator slots. Oily areas of the windings are wiped with a cleaning material soaked in gasoline. Winding areas with minor insulation damage (peelage, mechanical damage, exposed wires, etc.) are covered with insulating varnish or air-drying enamel, applying the varnish with a brush or spray.
Bandages that are torn, weakened or have lost their mechanical strength are carefully removed and banded the frontal parts of the windings, using taffeta tape when insulating the winding of heat resistance class A and glass tape when insulating classes E, B and F. The bandage is laid around the circumference of the frontal parts of the winding through one or two grooves using special awl (Fig. 4) with tension. Then the bandages are impregnated with one of the air-drying varnishes or enamels.
Places of the output wires of the stator winding of an electric motor with mechanical damage to the insulation are covered with several layers of insulating tape. Output wires are replaced with new ones if their insulation along the entire length has cracks, peeling or mechanical damage extending to the copper core. When replacing, remove the bandage from the frontal part of the winding and disconnect the damaged wire from the terminals of the coil group of the stator winding.
Rice. 4. Tools used to repair stator windings of electric motors:
awl for banding the frontal parts of the windings; b-knife; V -- mandrel for knocking out groove wedges; d - device for driving groove wedges.
Rice. 5. Connection of output wires with wires of coil groups:
A - twisting of copper wires; b- twisting of copper 1 wire with aluminum 2;
c-welding of copper 2 and aluminum 1 wires; G - insulating the junction with a Linoxin tube.
If the electric motor winding is wound with copper wire, then at a length of 35-40 mm, use a knife (Figure 4, b) to strip the ends of the wires of the coil groups and the output wire. The stripped ends are twisted, as shown in Figure 5a, and the length of the twist should not be less than 20-25 mm. The place where the wires are twisted is soldered with POS-30 or POS-40 solder or welded with a carbon electrode. When welding, one clamp of the transformer is connected to the twist, and the second to the carbon electrode (Fig. 5c). The arc voltage should be 16-18V.
If the electric motor winding is made of aluminum wire, then the ends of the wires of the coil groups are stripped to a length of 70-80 mm, and the end of the copper lead wire is stripped to a length of 50 mm. The stripped ends are connected by twisting in such a way that all the strands of the copper wire are inside four to five turns of aluminum wire and the end of the copper wire protrudes above the aluminum by 3-4 mm (Figure 5b). Using a brush, apply flux (rosin-25%, ethyl alcohol-75%) to the end surface of the twist and melt it with a carbon electrode until a high-quality connection of the wires is obtained. Melting begins from the end surface of the copper wire. After welding, the remaining flux is removed from the twist.
The junction of the wires is insulated by putting a twisted linoxin tube on it (Fig. 5, G) or by wrapping several layers of insulating tape. Then the frontal parts of the winding are banded, placing the turns of the bandage through one or two grooves around the circumference of the frontal part of the winding, and impregnated with air-drying varnish.
Weakened groove wedges are knocked out with a hammer using a mandrel (Fig. 4c ) and replaced with new ones made of hard wood (dry beech, birch, etc.). To drive in wedges, it is convenient to use a special device consisting of a guide and an extension (Fig. 4, d).
When removing and installing slot wedges, be careful not to damage the slot insulation and the insulation of the winding end parts.
Wedges made on the farm, at an enterprise or received from the manufacturer must be soaked and dried.
Soak the wedges for 3-4 hours in transformer or linseed oil, heated to a temperature of 100-120 ° C, then remove from the oil and allow it to drain for 20-30 minutes. Dry the wedges in a vertical position for 5-6 hours at a temperature of 100-110° C.
After driving, the ends of the groove wedges protruding beyond the ends of the stator are cut off, leaving 5-7 mm on each side.
To determine the moisture content of the insulation of the stator and phase rotor windings, the insulation resistance of the windings relative to the housing and between the windings is measured.
Rice. 6. Measuring the insulation resistance of electric motor windings.
Fig. 7 Cabinet for drying windings of electrical machines
If the insulation resistance is less than 1 MOhm at a temperature of 15°C, the motor windings must be dried. It is recommended to dry the windings of electric motors in the conditions of the electrical equipment maintenance area of a workshop of a farm or enterprise.
Several drying methods are used. It is most advisable in site conditions to dry the windings in a drying cabinet at a temperature of 80-90 ° C for 7-10 hours. For drying electric motor windings, you can use the OP-4443 cabinet (Fig. 7). Cabinet cover in open position serves as a platform for installing electric motors when removed from a crane beam or other lifting means, and the roller table on the lid and inside the cabinet serves for supplying motors to the cabinet chamber.
Rice. 8. Current diagram
drying the insulation of electrical machine windings (a):
1- winding; 2 - potential regulator
Scheme for drying the insulation of windings of electrical machines by losses in steel (b):
1 - machine stator; 2 - magnetizing winding.
The winding insulation is considered dried if its resistance at a steady temperature does not change within 2-3 hours.
When drying windings at the installation site of electric motors, one of three heating methods is usually used: external heating (thermoradiation method), heating by current passed through the windings of the electric motor, or induction heating.
To dry the windings with external heating, in most cases, infrared radiation lamps of the ZS type with a power of 250, 500, 1000 W, conventional lighting lamps with a power of 100-250 W or tubular electric heaters of the TEN type are used. Lamps and tubular electric heaters are placed in the stator bore so that the winding is heated evenly. During drying, the heating temperature and the insulation resistance of the windings are controlled. The heating temperature is controlled with a thermometer with a scale of 0-150 ° C, and the insulation resistance is controlled with a 500 V megger. At the beginning of drying, the temperature is measured after 15-30 minutes, and after the temperature has been established, every hour. The temperature of the winding in the hottest place should not exceed 90° C, and the time for heating the windings to a temperature of 70-90° C should be at least 2-2.5 hours. For electric motors of the series CX permissible temperature windings during drying is 110°C. To avoid heat dissipation, the stator and rotor should be protected with sheets of non-combustible material during drying.
When drying by current heating, the motor housing is grounded, the stator windings are connected in series or in parallel (Fig. 8, A) and connected to the secondary winding of the step-down transformer.
TBS-2 or OSO-0.25 lighting transformers can be used as a step-down transformer for drying the windings of electric motors with a power of up to 10 kW, and welding transformers can be used for electric motors of higher power. Before starting drying, use a rheostat or regulator to set the current in the electric motor windings to 60-80% of its rated value. During drying, the heating temperature of the windings and the insulation resistance are monitored.
To avoid insulation breakdown, only electric motor windings with an insulation resistance of at least 0.1 MOhm can be dried using the current method. Drying is especially dangerous DC windings with low insulation resistance, since during drying an electrolytic effect of current may occur.
To dry the windings by induction heating, a magnetizing winding is wound onto the stator frame (Fig. 8b). The windings of the electric motor are heated due to heat losses resulting from heating of the magnetic circuit.
In asynchronous electric motors for general industrial use with a power of up to 100 kW, the stator windings, according to the manufacturing method, are classified as template windings with soft coils. Soft coils are placed in semi-closed grooves with separate conductors, as if poured into the groove (random windings).
The rotors of the most common asynchronous motors are made in the form of a “squirrel cage” (short-circuited). The rotor grooves are filled with bare, uninsulated rods, the ends of which (ends) are connected to each other by rings or filled with aluminum with the simultaneous formation of closing rings.
Manufacturing of random stator windings. As a rule, damaged bulk windings with small-diameter wire are not repaired, but replaced with new ones, which are made from round wire on a winding machine using various templates. The groove insulation is released 10-15 mm above the surface of the stator bore. After laying the entire winding in the grooves, the protruding part of the insulation is cut off and bent inside the groove.
With a two-layer winding, one side of the coil is placed in the lower part of the groove, the second - in the upper part of the groove, located from the first groove at a distance equal to the winding pitch. When replacing one damaged coil, lift the top sides of all coils located between these grooves.
When laying the random winding, make sure that the wires do not cross. To do this, straighten the conductors with a special fiber plate, running it along the groove. An insulating pad is installed between the layers of the winding. After laying the winding, the groove is jammed.
Repair of the core winding of phase rotors. If the rods are destroyed, they are replaced with new ones. For rods with a large cross-section, as a rule, the insulation is restored, for which a diagram of the winding is drawn, the ends of the damaged rod and its attachment points are marked, and the shape of the bend of the frontal parts is drawn. Solder the ends of the damaged rod, straighten its frontal parts and remove the rod with pliers, having previously heated it with an electric current. .
The removed rods are freed from damaged insulation by firing. Damaged groove insulation is replaced with a new one of the same type. The groove is thoroughly cleaned. After laying the restored rod, its frontal parts are bent according to the template using keys.
When making new rotor windings or repairing them, pay special attention to the uniform arrangement of the frontal parts, ensuring minimal rotor imbalance.
Repair of short-circuited rotor winding. Most often, windings made by soldering or welding, the rods of which are connected to a short-circuited ring, are damaged. Damage to it is manifested in the disruption of contact between the rods and the short-circuiting ring, in the appearance of cracks, ruptures, shrinkage cavities and burns.
Cast short-circuited windings made of aluminum alloys are more reliable. If they are damaged, they are removed by smelting or chemically (in a caustic soda solution). Aluminum is re-poured into the cleaned rotor slots using one of the following methods: static, centrifugal, vibration or under pressure. Refilling rotors is difficult, as it requires special equipment. It is performed only at large repair bases.
When repairing the windings of electrical machines, a special winding tool is used.
The normal technology for impregnating winding insulation involves preliminary drying, impregnation with varnishes and final drying. Repeated impregnation of the windings ensures higher quality insulation. To create a moisture-proof film and smooth surface, on which dust accumulates less than on a rough one, after final impregnation and drying, the windings are covered with a topcoat varnish or enamel.
Pre-drying is carried out until moisture is completely removed from the winding and is carried out in special drying cabinets at an air temperature of 110-120 ˚C.
There are several methods of impregnation. The most common method for low-power machines is impregnation by immersion in an impregnating composition. After preliminary drying, the stators and rotors (armatures) with windings are cooled to a temperature of 60-70 ˚C and lowered into an impregnation tank with varnish. The anchor is lowered vertically, with the collector up, so that the collector cocks do not reach the surface of the varnish in the tank by 15 - 20 mm. Impregnation is continued until air bubbles cease to appear, which indicates that all pores of the winding are filled with varnish. Impregnating varnish is used with low viscosity. The required viscosity of the varnish is achieved by adding a solvent.
After impregnation, the winding is placed on a grid for 15 - 20 minutes so that excess varnish flows into the tank. During this time, thoroughly clean the core, rotor shaft, output ends and other surfaces where there should be no varnish film with a rag soaked in solvent. After this, the impregnated winding is dried in drying cabinet in order to remove solvent residues from the pores of the insulation and bake the varnish film. The insulation is considered well dried after impregnation if its varnish film does not stick to the fingers at all.
The frontal parts of the winding, which have not yet cooled down after drying, are covered with a layer of topcoat varnish or enamel, which is applied with a brush or spray. After this, the windings are finally dried in ovens or in air.
At repair bases that have special equipment, they use vacuum impregnation and pressure impregnation methods, or combine these methods. They are more advanced than those described above, but require more complex equipment.
Drying ovens at different repair bases vary in design. But they require mechanization of the supply of machine parts and air exchange, which ensures the removal of solvent vapors. The air in the furnace is heated with steam under high pressure or electric current, depending on the energy capabilities of the enterprise.
They use infrared rays to dry the windings of small electric motors. The winding can be irradiated directly at the repair site with infrared radiation lamps ZS-l, ZS-2, ZS-3, in which 80-90% of the supplied electrical energy is converted into thermal radiation energy. This method does not require bulky and complex drying ovens and cabinets.
Blowers can also be used for drying. In this case, a stream of hot air is directed to the frame, from the heating of which the winding also heats up.
The induction drying method is also common: due to losses in the steel, the latter heats up and dries the winding. Various methods for drying an electric motor are shown in Figure 2, a-c.
Figure 2 - Drying electric motor windings:
a - infrared lamps, b - blower, c - losses in the steel of the frame; 1 - motor, 2 lamps, 3 - temporary cabinet (booth), 4 - electric blower, 5 - insulated wire.
