Abstract technology of repair and maintenance of an asynchronous motor with a squirrel-cage rotor. Induction motor maintenance and overhaul Typical motor rewind charts

The scheme of the technological process for the repair of asynchronous motors and synchronous generators is shown in Figure 69 and does not require special explanations.
Since this manual is intended for students of electrification faculties of agricultural universities, future electrical engineers, the manual describes the most important, according to the authors, issues of repairing electrical machines. In addition, it should be taken into account that the State All-Union Order of the Red Banner of Labor Research Institute for the Repair and Operation of the Machine and Tractor Park (GOSNITI) has developed technological maps and guidelines for the overhaul of asynchronous electric motors, welding and automotive electrical equipment.

Scheme of the technological process of repair of squirrel-cage electric motors.
These documents are compiled in the form of tables, which list the numbers and contents of all technological operations, specifications and instructions for carrying out repairs, provides information about the equipment, fixtures and tools needed for repairs. Technological maps are supplemented with diagrams, sections, drawings. In the repair industry, various technical documentation is compiled, it is not the same at different plants and in individual departments, although the content of individual documents is close, and some of them are duplicated even at the same plants. Thus, Glavelectroremont of the METI recommends that its enterprises fill out a defective note and a list of defects after the fault detection of machines.
The content of the note includes the passport data of the machine before repair and the customer's wishes for changing them. It contains all dimensions of the stator and rotor cores and the winding data of the stator and rotor (winding type, number of slots, wire brand, number of turns in the coil, number of parallel conductors in a turn, number of coils in a group, phase, winding pitch, number of parallel branches, phase conjugation, wire consumption in kilograms, head extension, heat resistance class).
The list of defects records all the necessary operations throughout the machine, for example, the frame - weld cracks, repair locking surfaces, weld paws, repair fasteners and eyebolts, etc.
Each repaired machine is accompanied by a technological card, which contains information about the customer, technical specifications machine with its passport data, the value of the phase resistance, the cross section of the output ends and the insulation class, the size of the stator core and the number of slots, information about the winding data before repair and by calculation, information about the mechanical part - its condition, information about winding control and bench tests.
The technological map is signed by a troubleshooting technician, a foreman, a calculation engineer and QCD employees.
The duty officer for drying fills in the drying logs of electrical machines, which include: the customer, the order number, the passport data of the machine, the place of drying, information about the beginning of drying, the temperature of individual elements of the machine, the insulation resistance of the stator and rotor windings and the end of drying. The final results are certified by the person responsible for the drying and the head of the site.
Separately, the Quality Control Department maintains a book of test reports for each repaired machine. OTK. also draws up an act on the transfer of successfully tested machines to the finished product warehouse. The act indicates the repair number of the machine, type, power, insulation class, voltage, speed, form of execution, price list, repair cost, customer. The act is signed by the head of the QCD and the head of the warehouse.
Approximately the same form is drawn up an act of issuance of finished products indicating the total amount of repair costs. The act is signed by the management of the repair enterprise and the representative of the customer.
Technical documentation for the repair of transformers is more extensive in general and in terms of the content of individual documents. For example, the content of a troubleshooting note includes not only the passport data, the data of the HV and LV windings and the dimensions of the magnetic circuit, but also the mass of oil, the removable part and total weight transformer.
The note is signed by the persons who wound the windings and assembled the transformer, and the master.
Separately, a protocol for the analysis of transformer oil is filled out, in which the customer, the place, reason and date of sampling, the duration of the oil operation and the results of physical, chemical and electrical analyzes of the oil are indicated. Give a conclusion about the quality of the oil. The protocol is signed by the person who conducted the analysis, the site engineer.
For each transformer, a repair (revision) form is filled out containing the following information: about the customer, transformer passport, work and measurements performed during the repair process for all components and parts of the transformer (tank, radiator, expander, exhaust pipe, tank and expander fittings, transport fixtures, HV, MV and LV bushings, valve and bushing flange cover seals, magnetic circuit and its grounding, HV, MV, LV windings and the state of their pressing, voltage switch, winding insulation details, taps and circuit, oil, additional data), o drying (drying method, its beginning and end, temperature during drying, inspection and crimping after drying, DC resistance of windings in phases of all windings at the measurement temperature), preliminary tests (determination of transformation ratios for all windings and taps, insulation resistance, checking the electrical strength of the insulation), on the final tests (data from the experiments of idling and short circuit , transformation ratio test, resistance of all windings in phases at measured temperature, winding connection group, winding capacitance ratios at different frequencies, etc., insulation test with applied voltage, turn insulation test, oil strength). At the same time, data on the devices used in the tests are entered into the form. The form is signed by the person who conducted the tests, the QCD foreman, the workshop foreman and Chief Engineer.
The transformer drying logs and the protocol for the analysis and testing of transformer oil are attached to the form.
For repaired transformers, certificates of acceptance of finished works are drawn up. In the process of repair, they draw up a limit card-report on the consumption of materials, on the basis of which the cost of repairing transformers is determined. Defection of electrical equipment. Fault detection methods
Defektirovanie is the definition of machine malfunctions during operation or repair. There are two stages - fault detection of the assembled machine and after its disassembly.
Fault detection of a machine or apparatus is one of the most critical operations, since undetected malfunctions can lead to the destruction of the machine in operation, an accident, and an increase in the duration and cost of work during repeated repairs.
Electrical equipment is characterized by the presence of two parts - electrical and mechanical. When fault-finding the mechanical part of electrical equipment, they check the condition of the fasteners, make sure that there are no cracks in one or another part, determine wear and tear and compare it with permissible standards, measure air gaps and compare with tabular values, etc.
All detected deviations from the norms are recorded and entered in the list of defects or a repair card, the forms of which are different at different plants, but the content is almost the same.
Malfunctions in the electrical part of a machine or apparatus are hidden from human eyes, so they are more difficult to detect. The number of possible faults in the electrical part is limited to three:
open circuit;
the short circuit of individual circuits between themselves or the circuit of the circuit (circuits) on the body;
the closure between each other of the turns of the winding (the so-called inter-turn or turn closure).
These faults can be identified using the following four methods:
test lamp or resistance method (ohmmeter);
method of symmetry of currents or voltages;
millivoltmeter method;
electromagnet method.
Consider the definition of faults in the assembled machine or apparatus.
An open in a winding without parallel circuits can be determined by using a test lamp. If there are two or more parallel branches in the winding, a break is determined with an ohmmeter or an ammeter and a voltmeter. The obtained value of the resistance of the winding (for example, the armature winding of a DC machine) is compared with the calculated or passport value, after which a conclusion is made about the integrity of the individual branches of the winding. Breaks in multi-phase machines and devices that do not have parallel branches can be determined by the current or voltage symmetry method, but this method is more complicated than the previous one.
It is somewhat more difficult to determine a break in the rods of squirrel-cage rotors of asynchronous electric motors. In this case, resort to the method of current symmetry.
Experience in determining breaks in rods is as follows. The rotor of the electric motor is braked and the stator is supplied with a voltage reduced by 5 ... 6 times compared to the rated voltage. An ammeter is included in each of the phases of the stator winding. With good stator and rotor windings, the readings of all three ammeters are the same and do not depend on the position of the rotor. When the rods break in the rotor, the readings of the instruments are different, most often
two ammeters show the same currents, and the third shows a smaller current. When the rotor is slowly rotated by hand, the readings of the instruments change, the reduced current value will follow the rotation of the rotor and goes from one phase to another, then to the third, etc.
This is explained by the fact that when the rotor turns, the damaged rods move from the zone of one phase to the zone of another. A stalled induction motor is like a transformer in short circuit mode. Breakage of the rod is equivalent to transferring the damage zone from the short circuit mode to the load mode, which leads to a decrease in the current in the stator winding in that part of it that interacts with the damaged rod.
If several rotor rods break, the readings of all ammeters may be different, but they, as mentioned above, will cyclically change and follow one after the other (passing through the phases of the stator winding) with slow rotation of the rotor. Different readings of ammeters, independent of the rotation of the rotor, indicate damage or defects in the stator winding, but not the rotor.
The location of the break in the windings of the rotors of squirrel-cage motors is determined using an electromagnet. The rotor, mounted on an electromagnet, is covered with a sheet of paper, on which steel filings are poured. When the electromagnet is turned on, the sawdust is located along the entire rods and is absent in the break zone.
Breaks in the armature windings of DC machines are determined using an ohmmeter (millivoltmeter).
The closure of individual electrical circuits of electrical equipment to the housing or to each other is determined using a test lamp. Often in this case, megohmmeters are used. The latter should be preferred, since they are easy to determine the circuit with a relatively high resistance at the point of contact between the circuits or with the case.
The short circuit between the sections lying in different layers of the grooves of the section armatures on the body is determined using an ohmmeter (millivoltmeter).
The coil circuit in multi-phase electrical machines and devices is determined by the method of symmetry of such and voltages or by special devices, for example, the EJI-1 type.
So, turn short circuits in the windings of three-phase electric motors are determined at idle their operation using the current symmetry method (the readings of all three ammeters included in each phase of the stator winding should be the same in the absence of turn short circuits), and turn short circuits in the stator windings of synchronous generators are determined at idle using the voltage symmetry method (the readings of all three voltmeters connected to the stator winding terminals must be the same).
When determining turn short circuits in the windings of three-phase transformers, both the current and voltage symmetry method is used.

Rice. 7. Scheme for determining turn short circuits in equipment coils.
Turn short circuits in the windings of single-phase electrical machines and transformers are determined with an ohmmeter or ammeter. When determining turn short circuits in the excitation coils of DC machines, it is advisable to use low-voltage alternating current rather than direct current to increase the sensitivity of the test by selecting the appropriate instruments (ammeter and voltmeter).
It should be noted that the turn short circuit in the windings of electrical equipment operating on alternating current is accompanied by a sharp increase in current in the damaged winding, which, in turn, leads to a very rapid heating of the winding to unacceptable limits, the winding starts to smoke, char and burns.
The place of turn circuits in the stator windings of AC electrical machines is determined using an electromagnet. The place of turn short circuits in the armature windings of DC machines is determined with an ohmmeter (millivoltmeter).
Usually damaged coils of transformers are not defective, but if necessary, the electromagnet method can be used (Fig. 7).
The fault detection of DC and AC machines and transformers during repair is described in detail in the workshop on installation, operation and repair of electrical equipment.

Dismantling of electrical machines. Removing the old winding

Dismantling electrical machines into their component parts is not difficult. It is only necessary to mechanize the performance of individual operations as much as possible, using electric or hydraulic wrenches, pullers, hoists, etc., and also be careful when removing the rotors of large machines so as not to damage the stator iron packages or its winding with the rotor.
The most time-consuming operation during disassembly is the removal of the old winding. This is done by the following methods: mechanical, thermomechanical, thermochemical, chemical and electromagnetic.
The essence of the mechanical method lies in the fact that the body of the electric machine with stator steel packages and winding is installed on a lathe or milling machine and cutter or
one of the frontal parts of the winding is cut with a cutter. Then, with the help of an electric or hydraulic drive, the remaining part of the winding is removed (pulled out) from the grooves (with a hook for the remaining frontal part of it). However, with such a removal of the winding, there are remains of insulation in the grooves, and additional costs are required for their removal.
2. With the thermomechanical method of removing the old winding, an electric machine with a cut off end of the winding is placed in a kiln at a temperature of 300 ... 350 ° C and kept there for several hours. After that, the rest of the winding is easily removed. Often the machine is placed in a furnace with the entire winding (none of the ends of the winding is cut off), but in this case, after firing, the winding is removed from the grooves only manually.
It is difficult to create a uniform thermal field in a kiln. Quite often, the winding insulation ignites in the furnace, leading to a sharp increase in temperature in the furnace, especially in some of its zones. When the temperature rises above the permissible level, machine bodies can warp, especially aluminum cases. Therefore, machines with aluminum bodies are not recommended to be fired. Some enterprises investigate the distribution of temperatures inside the furnace during its operation and determine the zones in which it is possible to locate electrical machines with aluminum casings.
During firing in a furnace, stator steel sheets are annealed, specific losses in steel are noticeably reduced and efficiency increases; cars. However, the lacquer films between the steel package and the housing and between the individual steel sheets burn out. The latter leads to the fact that after 2 ... 3 firings, the tight fit between the package and the body is broken, the package begins to rotate in the machine body, and the pressing of the package is weakened. Therefore, the firing of the insulation of the windings of machines in molten salts (caustic or alkali) can be considered progressive.
Roasting in molten salts is carried out at a temperature of 300°C (573K) with aluminum cases and 480°C (753 K) with cast iron for several minutes. The complete absence of air access to the firing object, as well as the ability to control the temperature within the required limits, make it possible to use this firing method for machines with aluminum casings. Warping of the latter is completely excluded.
At thermo chemical method removing the winding, the electrical machine prepared for firing (one of the frontal parts of the winding is cut off) is lowered into a container with a solution of caustic soda or alkali. The machine is in solution at a temperature of 80...100°C for 8...10 hours, after which its winding can be easily removed from the grooves of the stator packs. With this method, no warping of the hulls can occur. This method is especially justified for oil-bitumen insulation of windings.
In the chemical method, an electrical machine with a winding is placed in a container with washing liquid of the MF-70 type. This liquid is volatile and toxic, therefore, when working with it, safety regulations must be observed. The technology for removing the windings is as follows: loading the container with repaired machines, sealing the container, filling it with liquid, the reaction process, which usually takes night time off, removing the liquid, purging the container freed from liquid, clean air, depressurization and opening of the container, excavation of electrical machines and removal of the winding from the stator slots.

5. The electromagnetic method is as follows. A single-phase transformer is made with a removable armature and one removable, more precisely, replaceable core. A magnetizing winding is wound on an irreplaceable rod for mains voltage. One or more motor stators are put on the second removable rod, the winding insulation of which must be burned. The diameter of the replaced rod is selected in such a way as to obtain the smallest (about 5 mm) gap between the stator bore and the rod. The method is convenient in that with it it is possible to regulate the heating temperature of the stator by changing the voltage supplied to the magnetizing winding or switching the number of its turns. With this method, machines with both cast iron and aluminum bodies can be fired.

By design windings of electrical machines are divided into three types: concentric, loose and template. The latter, in turn, are divided into windings with continuous compounded insulation and sleeve. They are used in large machines with a voltage of 3.6 kV and higher, so they are not considered in this book.
In practice, the repair of windings consists in removing the old one and making a new winding, which has the same or improved data of slot insulation and winding wire.
Concentric winding is the most obsolete, laborious and is used only in electrical machines with closed slots. The manufacture of this winding consists of the following basic operations: the manufacture of slotted insulating sleeves using templates, the material for which is selected depending on the voltage of the machine and its heat resistance class; laying sleeves in grooves; filling the sleeves with metal or wooden studs according to the dimensions of the insulated winding wire; the choice of a winding scheme, in which the smallest voltages are obtained between adjacent conductors in the groove of the machine; preparation of the wire for winding coils, which consists in removing the insulation at the ends of the wire prepared for winding the coil and waxing it to facilitate pulling it through the grooves; winding with two winders of the smallest coil using special templates for forming the frontal parts of the coil; winding the remaining coils, their connection and isolation.
In the manufacture of bulk windings, insulating slot boxes are first prepared and placed in the grooves. In this case, it should be borne in mind that in machines of the old series, the slot boxes consist of two layers of electric cardboard and one layer of varnished cloth. They were replaced by slotted boxes, consisting of film-electrocardboard, and at present, in small machines of new series, only one thin layer of insulating film is used. Under these conditions, the use of new materials, including winding wires, when repairing old-series electric machines significantly increases their reliability and, if necessary, can be accompanied by a noticeable increase in machine power. On the contrary, when repairing machines of new series, it is necessary to use only appropriate high-quality materials and winding wires, otherwise the repair of the machine will lead to a decrease in its reliability, deterioration in technical and economic indicators and a sharp decrease in its power. In addition, it is necessary to take into account the narrow specialization and mechanization of work at electrical engineering plants and the lower level of work technology at repair enterprises, which also affects the quality of work, the fill factor of the machine slot and its reliability. The next winding operation is winding on special, size-adjustable coil templates. This is followed by the laying of coils in grooves, the installation of wedges, which can also be used in low-power machines of new series, as well as a film, connecting and bundling the winding with insulating cords or stockings with the installation of insulating interphase spacers on the frontal parts of the winding. If it is necessary to connect individual coils, they are isolated with linoxin, PVC or glass-lacquer tubes.
Connections between the coils can be made either by soldering (the ends to be joined are tinned, twisted and dipped in a bath of molten solder), or by resistance welding using manual tongs with a graphite electrode.
Drying of the windings of electrical machines, before and after impregnation, is carried out in drying ovens (convective method), losses in stator or rotor steel (induction method), losses in windings (current method) and infrared irradiation (radiation method).
Usually, electrical repair enterprises have vacuum or atmospheric drying ovens, the volume of which is determined at the rate of 0.02 ... 0.04 m 3 /kW of the power of the machines for which the oven is intended. The heater can be electric, including lamp, steam or gas. The heater power is determined at the rate of approximately 5 kW per 1 m 3 of the furnace volume. Rational air circulation must be ensured in the oven. Thus, the drying power is the greater, the more number and power of the machines being dried. Drying time ranges from several hours (6...8) for small machines to several tens of hours (70...100) for large machines.
Drying machines by induction requires a magnetizing winding. This method is useful for drying large machines that are best dried at installation or repair sites rather than in a drying oven. This method is more economical than the previous one both in terms of power consumption and drying time.
Drying with a current method is even more beneficial. The duration of drying is reduced in comparison with drying in ovens by 5...6 times, and power consumption - by 4 or more times. The disadvantage of this drying method is the need to have an adjustable non-standard voltage power supply. In this case, the connection schemes of the windings can be different. The drying temperature and its mode depend on the heat resistance class of the machine and the brand of impregnating varnish. The completion of drying can be judged by the established resistance of the insulation being dried (at a given constant temperature).
The most common method of impregnation is the immersion of a winding heated to 60 ... 70 ° C in a varnish of approximately the same temperature. The number of impregnations depends on the purpose of the machine, in agricultural production it is recommended to carry out up to three impregnations. The duration of impregnation is 15...30 minutes for the first and 12...15 minutes for the last.
After vacuum drying, pressure impregnation can be applied for critical machines. But to provide the first and second processes, relatively complex equipment is required.

electromechanical work includes: repair of machine bodies, end shields, shafts, bearing assemblies, active iron of the stator or rotor, collectors, slip rings, brush devices and short-circuited mechanisms, poles, squirrel cages and output boxes. In addition, these works include shrouding of rotors and armatures and their balancing.
In the conditions of electrical repair enterprises of the State Committee for Agriculture, the iron of the stator and rotor, the poles and squirrel cages of the rotors are usually not repaired. Cars with such damage are considered non-repairable, they are not accepted for repair and are written off for scrap.
Repair of housings and end shields, as a rule, consists in the elimination of fractures and cracks and is carried out by welding.
Currently, almost all electrical machines have rolling bearings, maintenance and repair of which is much easier than plain bearings.
Rolling bearings are usually replaced when worn. If there are no bearings of the required standard sizes, bearings with other sizes can be used, but the new bearing must correspond in its load capacity to the replaced one. In this case, internal or external auxiliary (repair) bushings are used, the fit (coupling) of which is carried out by pressing (with an interference fit), and auxiliary thrust rings are used under the outer ring of the bearing.
Roller bearings can be replaced with ball bearings in cases where significant axial forces are not observed during operation of the machine (the run-up of the mechanism shaft does not exceed the run-up of the electric motor).
Ball bearings have a tight fit on the shaft, therefore, before landing on the shaft, they are heated in an oil bath to a temperature of 80...90°C.
Collector repair can be carried out with or without disassembly. Repair without disassembly consists in turning (on lathe or in their own bearings), peeling, grinding and polishing. The cutting of the collector (using a cutter on the machine, a hacksaw blade or a special scraper) is performed at each repair of the collector, even if it has not been grooved.
When repairing or replacing the insulation between the collector plates, one should strive not to disassemble the collector completely, but to use a detachable clamp, which significantly reduces the labor costs for disassembly and especially for assembly of the collector. For low-voltage machines, new collars can be molded directly during assembly of the collector without the use of special molds.
The repaired, fully assembled manifold is heated in a furnace to a temperature of 150 ... 160 ° C, tested on a machine for mechanical strength at a frequency of rotation 1.5 times higher than the nominal one, and checked for the absence of short circuits between the plates and between the plates and the bushing.
Slip rings are repaired if their thickness in the radial direction reaches 8 ... 10 mm (less than 50% of the original). The design of the assembly with slip rings can be very diverse: a split sleeve, insulation from electric cardboard, flexible micanite and rings; solid sleeve, split sleeve made of sheet steel, insulation made of electric cardboard and rings; a continuous bushing with insulating figured rings, between which the machine rings are located; solid bushing, mikafolium or micanite insulation and rings. All designs of slip ring assemblies, except for the last one, are assembled with an interference fit in a cold state.
The slip rings are checked for the absence of short circuits between them and the housing and runout (radial runout should not be more than 0.1 mm at a speed of up to 1000 rpm and 0.05 mm at a higher speed, and axial runout should not exceed 3 .., 5% of the ring thickness).
Repair of brush devices (traverse with fingers, brush holders with springs and clips and brushes) most often consists in restoring the insulation of the brush holder fingers, reliable contact between the bundles and the brush, adjusting the brush holder springs and installing, adjusting and running in the brushes. The brush holders are insulated with getinax end washers and bakedized paper on the neck of the finger with a thickness according to the repair process chart.
The choice of brushes depends on the purpose of the machine and the features of its operation. It is recommended to install electrographite brushes (EG) in exciters of an AC machine, allowing a current density of 9 ... 12 A / cm 2 and a linear speed of rotation of 40 ... 45 m / s; in crane engines - carbon-graphite (T and UG) with parameters of 6 A / cm 2 and 10 m / s and electrographite; in low-voltage generators (up to 20 V) - electrographite and copper-graphite (M and MG) with parameters 14 ... 20 A / cm 2 and 15 ... 25 m / s; in automobile electric machines - copper-graphite; in machines with slip rings - graphite (G), electrographite and copper-graphite.
The pressure of the brushes is recommended in the range from 1500 to 2000 Pa.
Repair of the short-circuit mechanism consists in restoring the worn side ribs of the short-circuit ring, fork pins and spring contacts by welding and surfacing, or replacing the worn part with a new one.
Stockings or keeper tape are used to bandage the stator windings of machines of relatively low power. The frontal parts of the windings of various coils and phases are fastened with a bandage into a single whole unit, which, after impregnation and drying, becomes monolithic. This provides the necessary mechanical strength of the winding during starts and sudden overloads of the machine. In large machines, so-called bandage rings are used, they are placed on top of the outer frontal parts of the machine coils. Each coil is tied with a keeper tape to the ring.
A special role is played by the shrouding of the windings of the rotors and armatures of machines, which experience not only electrodynamic loads during the operation of the machine, but also centrifugal forces. Rotors and anchors are shrouded on turning or special shrouding machines equipped with devices for tensioning tinned steel shrouding wire.
A layer of insulation made of micanite and electric cardboard is laid between the winding and the wire. With a wire diameter of 0.6 to 2 mm, the wire tension should be from 200 to 2000 N, the number of turns of the bandage is calculated for centrifugal forces, which should not exceed 400 N per 1 mm 2 wire section. The bandages are soldered around the entire circumference to turn them into a continuous ring.

In repair practice, parts from various materials are restored using manual arc and gas surfacing and welding, automatic surfacing and welding under a layer of flux, vibro-arc surfacing in a coolant jet, welding and surfacing in a shielding gas environment, electric spark processing and build-up both in air and in a liquid medium, metallization, ostalivaniya, chemical nickel plating.
When repairing electric motors, a relatively large amount of work is to increase the seating surfaces. For these purposes, vibro-arc surfacing with flux-cored wire and surfacing in a carbon dioxide environment are widely used. The first is used to restore shafts, axles and pins with a diameter of more than 30 mm. At the same time, the hardness of the surfacing layer is 1.5...2 times higher compared to the hardness of the layer obtained by vibro-arc surfacing in liquid. This improves the quality of the surfacing layer.
After surfacing, a groove is made and the surface is polished, and if necessary, grooves (spline grooves) are milled.
For finishing shaft surfaces instead of grinding, hardening the surface layer to a depth of 0.2 ... 0.3 mm, increasing wear resistance and fatigue strength of the part, an electromechanical processing method is used, which consists in the fact that when processing a part on a lathe, a part and a cutter a voltage of 2 ... 6 V is applied and a current of 350 ... 1500 A flows at the place of their contact.
Cast iron beds and bearing shields are welded with gas welding. Before surfacing, the parts are heated in a furnace to a temperature of 300 ... 400 ° C, while cast iron electrodes are used, borax or other mixtures are used as a flux.
After surfacing, the parts are fired at the same temperature for 4...6 hours, after which they are slowly cooled in the switched off furnace (12...14 hours). Recently, at the repair enterprises of the Goskomselkhoztekhnika system, installations for galvanic electron rubbing are used to restore bearing seats in parts housings.
Restoration can be subjected to holes with a diameter of 50 to 150 mm. The principle of operation of the installations is based on the electrolysis process, accompanied by metal deposition on one of the electrodes. The part to be restored is connected to the negative pole of a power source with a voltage of 24 to 30 V, for example, a PSO-300 converter. An electrode wrapped in a material capable of absorbing (absorbing) electrolyte is inserted into the restored hole. The electrolyte is supplied to the absorbent material by means of a pump with a flow rate of 20 l/min. When the electrode rotates at a frequency of 20 to 40 rpm (using any vertical drilling machine) an electrolytic bath is created in the absorbent material, in which the electrolysis process takes place. A set of electrodes consists of steel parts wrapped with absorbent material, which can be used as cotton fabric, for example, keeper tape with a layer of up to 2.5 ... 3 mm. The gap between the absorbent layer and the surface of the growing hole is 1.5...2 mm.
To build up parts made of steel and cast iron, an electrolyte of the following composition is used: zinc sulfate - 600 ... 700 g per liter warm water and boric acid- 20...40 g per liter of warm water. The acidity (concentration) of the electrolyte pH = 3...4, it is checked monthly, and once a month the electrolyte is completely replaced.
For aluminum parts, a solution of 150 g of aluminum sulfate in a liter of water is used as an electrolyte. The acidity of the electrolyte is pH=3...3.5.
The current density during etching, which precedes the growth, is 1 ... 1.5 A / cm 2 (etching duration 8 ... 10 s) and when growing 2 ... 3 A / cm 2. The growth rate is 20...30 µm/min.
Preparing the bearing shield for restoration consists in cleaning it with fine sandpaper, degreasing it with a rag soaked in gasoline or acetone, and drying it. With the extension method described, it is necessary to insulate the table of the drilling machine in order to use the body and table as clamps of different polarity. For safety reasons, the electric motor is isolated from the machine body. The worker serving the installation works in glasses, a rubber apron and rubber gloves. The floor of the machine is lined with rubber mats. Installing and removing parts is only allowed when the power is off.
Recently, elastomers have been used to restore seats for bearings, in particular GEN-150 (V). To dissolve 20 parts by weight of elastomer, 100 parts by weight of acetone are needed. The part to be restored is cleaned of dirt, corrosion, degreased, cleaned with acetone and dried. The elastomer is applied to the part through a tube.

Introduction

Main part

1. Device and principle of operation induction motor with squirrel-cage rotor

2. Possible malfunctions of an asynchronous motor with a squirrel-cage rotor and ways to eliminate them

3.Tool used

4. Technological map of repair and maintenance of an asynchronous motor with a squirrel-cage rotor

Economy

Labor protection and ecology

Conclusion

Bibliography

Introduction

Maintenance of electrical installations of industrial enterprises is carried out by hundreds of thousands of electricians, on whose qualifications the reliable and uninterrupted operation of electrical installations largely depends. The correct organization of the work of an electrician and the competent conduct of the operation of electrical installations become a very difficult and responsible matter, since any error in operation can lead to significant material damage, failure of expensive equipment, large losses of products, and wasteful use of electricity.

Relevance chosen topic: against the backdrop of industrial development, the role of reliable and powerful electric machines with high efficiency is increasing.

For my work, I chose the topic "Technology of repair and maintenance of an asynchronous motor with a squirrel-cage rotor", since such an motor is one of the most common types of electric motors.

Objective: to study and describe the device, the principle of operation, the technology of repair and maintenance of an asynchronous motor with a squirrel-cage rotor.

Tasks:

· to analyze the literature and technical documentation on the chosen topic;

study and describe the device, the principle of operation, possible faults asynchronous motor with a squirrel-cage rotor;

draw up a technological map for the repair and maintenance of an asynchronous motor;

make economic calculations of repair work;

Analyze the environmental situation at the site of the internship.

1. Main body

.1 Design and principle of operation of an asynchronous motor with a squirrel-cage rotor

An asynchronous machine is an AC electric machine whose rotor speed is not equal (in motor mode less) to the speed magnetic field generated by the stator winding current. They are mainly used as electric motors and are the main converters of electrical energy into mechanical energy.

An induction motor consists of two main parts separated by an air gap: a stationary stator and a rotating rotor. Each of these parts has a core and a winding. In this case, the stator winding is connected to the network and is, as it were, primary, and the rotor winding is secondary, since energy enters it from the stator winding due to the magnetic connection between these windings. According to their design, asynchronous motors are divided into two types: motors with a squirrel-cage rotor and motors with a phase rotor. Consider the device of a three-phase asynchronous motor with a squirrel-cage rotor. This type of motor is the most widely used.

Fig.1. Asynchronous squirrel-cage motor

1-shaft; 2-outer bearing cover; 3-roller bearing; 4-inner bearing cover; 5-bearing shield; 6-box of conclusions; 7-stator winding; 8-rotor winding; 9-stator core; 10-rotor core; 11-motor housing; 12-fan shroud; 13-fan; 14-ball bearing; 15-ground bolt; 16-hole engine mounting bolt

In the stator bore there is a rotating part of the motor rotor, consisting of a shaft and a core with a short-circuited winding. Such a winding, called a "squirrel wheel", is a series of metal, aluminum or copper rods located in the grooves of the rotor core, closed on both sides by short-circuit rings. The rotor core also has a laminated structure, but the rotor sheets are not coated with insulating varnish, but have a thin oxide film on their surface. This is sufficient insulation to limit eddy currents, since their magnitude is small due to the low frequency of magnetization reversal of the rotor core. For example, at a mains frequency of 50 Hz and a nominal slip of 6%, the remagnetization frequency of the rotor core is 3 Hz. The squirrel-cage rotor winding in most motors is done by casting the assembled rotor core with molten aluminum alloy. At the same time, short-circuiting rings and ventilation blades are cast simultaneously with the winding rods. The rotor shaft rotates in rolling bearings located in end shields.

The ends of the phase windings are brought out to the terminals of the terminal box. Typically, asynchronous motors are designed to be connected to a three-phase network for two different voltages, which differ by a factor. For example, the motor is designed to be connected to a network for voltages of 380/660 V. If the line voltage is 660 V, then the stator winding should be connected with a star, and if 380 V, then with a triangle. In both cases, the voltage on the winding of each phase will be 380V. The conclusions of the phase windings are placed on the panel in such a way that it is convenient to connect the phase windings by means of jumpers, without crossing the latter. In some low power motors, there are only three clamps in the terminal box. In this case, the motor can be connected to the network for one voltage (the connection of the stator winding of such a motor with a star or a delta is made inside the motor).

1.2 Possible malfunctions of a squirrel-cage induction motor

An external malfunction can be:

insufficient ventilation of the engine;

violation of the contact of the device with the network;

overload of the device;

incompatibility of the input voltage with the operating requirements of the motor.

The following can be considered internal breakdowns of an asynchronous motor:

bearing failures;

broken rotor shaft;

weakening of the grip of the brushes;

stator mounting failures;

the appearance of grooves on the collector or slip rings;

short circuits between turns of windings;

insulation penetrating the body;

winding desoldering;

wrong polarity.

Motor mounting:

The electric motor, delivered to the place of installation from the manufacturer or from the warehouse where it was stored before installation, or from the workshop after the revision, is installed on the prepared base.

Depending on the conditions, cast iron or steel plates, welded metal frames, brackets, sleds, etc. are used as bases for electric motors. Plates, frames or sleds are aligned axially and in a horizontal plane and fixed on concrete foundations, ceilings, etc. with the help of foundation bolts, which are embedded in prepared holes. These holes are usually left when concreting foundations, laying wooden plugs in advance in appropriate places.

Shallow holes can also be punched into finished concrete bases using electric and pneumatic hammers equipped with high-performance tools with tips made of hard alloys. The holes in the plate or frame to secure the motor are usually made by the manufacturer, who supplies common stove or a frame for the electric motor and the mechanism driven by it.

If there are no holes for the electric motor, the base is marked and holes are drilled at the installation site. To perform these works, the mounting and installation dimensions of the installed electric motor are determined (see figure), namely: the distance between the vertical axis of the motor and the end of the shaft L6 + L7 or the end of the mounted half-coupling, the distance between the ends of the half-couplings on the shafts of the electric motor and the mechanism driven by it, the distance between the holes in the legs along the motor axis С2+С2, the distance between the holes in the legs in the perpendicular direction С+С.

In addition, the height of the shaft (axle height) on the mechanism and the height of the motor axis h must be measured. As a result of these last two measurements, the thickness of the paw pads is preliminarily determined.

For the convenience of centering the electric motor, the thickness of the pads should be provided within 2 - 5 mm. The lifting of electric motors on the foundations is carried out by cranes, hoists, winches and other mechanisms. Lifting of electric motors weighing up to 80 kg in the absence of mechanisms can be done manually using decks and other devices. The electric motor installed on the base is preliminarily centered with a rough adjustment along the axes and in the horizontal plane. The final alignment is made when the shafts are mated.

1.3 Tool used

In the process of maintenance and repair of a squirrel-cage induction motor, the following tool is used:

Alignment ruler

Staples and strings

Rulers with pulleys of different widths.

Wrenches 6 - 32 mm - 1 set.

Files - 1 set.

Set of heads - 1 set.

Metal brush - 1 pc.

Repair knife - 1 pc.

Screwdriver set - 1 set.

Locksmith's screwdriver - 1 pc.

Dies 4 - 16 mm - 1 set.

Taps 4 - 16 mm - 1 set.

A set of drills 3 - 16 mm - 1 set.

Mount - 1 pc.

Pliers - 1 pc.

Chisel - 1 pc.

Drill - 1 pc.

Core - 1 pc.

Flat brush - 2 pcs.

Hammer - 1 pc.

Shovel - 1 pc.

Basting brush - 1 pc.

1.4 Technological map of repair and maintenance of an asynchronous motor with a squirrel-cage rotor

Security measures

The electric motor must be de-energized, the AB is turned off, grounding is installed, posters are hung out. Apply portable grounding to the input ends of the electric motor cable. Secure the work site. Work with PPE. Work with trusted instruments and tested power tools and fixtures.

The composition of the brigade

An electrician for the repair of electrical equipment with an electrical safety group of at least the third. Electrician for the repair of electrical equipment with the third electrical safety group.

2. Economy

Conclusion: repair of parts of an asynchronous motor is more cost-effective than replacing them.

3. Labor protection and ecology of EVRAZ NTMK converter production

I had an internship at the converter shop of EVRAZ NTMK and had the opportunity to analyze the environmental situation and labor protection conditions at the plant in general and the converter shop in particular. squirrel-cage rotor induction motor

The EVRAZ NTMK converter shop celebrated its 50th anniversary in autumn 2013. This is one of the most modern steelmaking facilities in Russia. Over the past few years, a full-scale reconstruction has been carried out here. Today the workshop includes a converter department with four 160-ton converters; out-of-furnace steel processing section, which includes four ladle furnaces and two circulating degassers; department of continuous casting of steel from four CCMs. An iron desulfurization unit is in operation, which allows the production of steel with a minimum sulfur content.

Reducing the negative impact of production on the environment and the population of Nizhny Tagil is the goal of the entire environmental policy of the Nizhny Tagil Iron and Steel Works. In recent years, the plant has invested significant funds in the technical reconstruction of the enterprise, which, along with modernization, without fail solved the environmental problems of the city.

By 2007, the following facilities were built and put into operation: the ONRS complex in the converter shop, consisting of continuous casting machines No. 1, 2, 3, 4, ladle furnace No. 1, 2, 3, and a degasser;

Sergey Permyakov, Head of the Environmental Protection Department at NTMK, noted that only thanks to the technical re-equipment of converter No. 4, it was possible to reduce emissions into the atmosphere by almost 500 tons per year. Dust emissions decreased by 30 tons as a result of overhaul of dust and gas trapping units in the blast furnace and converter shops. Major overhauls were also carried out in the dirty water recycling cycle of the blast furnace, rolling and converter industries.

The implementation of these measures made it possible to reduce the content of oil products in water bodies by 14 tons, zinc by 977 kg, fluorine by 8,309 kg, and iron by 466 kg. Together with environmentalists from Nizhny Tagil, this technology was also used at the Nizhny Tagil reservoir.

In June 2010, OAO NTMK successfully completed an external recertification audit of its environmental management system. Based on the results of the audit, the certificate of compliance with the requirements of the international standard ISO 14001 was extended.

The implementation of environmental protection measures over the past five years has made it possible to reduce annual emissions of pollutants into the atmosphere by 32,000 tons.

Conclusion

In the course of this work, I analyzed the literature and technical documentation on the chosen topic, studied and described the device, principle of operation, possible malfunctions of an asynchronous motor with a squirrel-cage rotor, compiled a technological map of repair and maintenance, made an economic calculation of repair work, described the environmental situation on the site passing industrial practice. Thus, it is possible to consider the set goals of the task fulfilled.

The knowledge and skills acquired in the course of this work, acquired in industrial practice, will be useful in my future professional activities.

Bibliography

1. Lobzin S.A. Electric cars. - M.: Information Center "Academy", 2012.

Moskalenko V.V. Electrician's Handbook: Handbook. - M.: ProfObrIzdat, 2002.

Moskalenko V.V. Electric drive. - M.: Information Center "Academy", 2000.

Nesterenko V.M. Technology of electrical work. - M.: Information Center "Academy", 2004.

Sibikin Yu.D., Sibikin M.Yu. Maintenance, repair of electrical equipment and networks of industrial enterprises. - M.: IRPO; Ed. Center "Academy", 2000.

Sibikin Yu.D., Sibikin M.Yu. Technology of electrical work. - M.: Information Center "Academy", 2000.

Sibikin Yu.D. Electrical safety in the operation of electrical installations of industrial enterprises. - M.: Ed. Center "Academy", 2007.

Page 10 of 17

3.11 Technological map of the current repair of asynchronous electric motors 6kV PEN.

After assembly, make a control measurement of the motor insulation resistance and absorption coefficient with a 2500V megohmmeter. The insulation resistance must be at least 40 MΩ, the absorption coefficient must be at least the value specified in clause 1.3.2.

3.12 Technological map of the current repair of asynchronous electric motors 6 kV TsN.

After assembly, make a control measurement of the motor insulation resistance and absorption coefficient with a 2500V megohmmeter. The insulation resistance must be at least 40 MΩ, the absorption coefficient must be at least the value specified in clause 1.3.2. When assembling, check the condition of the oil indicators, for which:

a) clean the oil gauges from external contaminants;

b) unscrew the damping bolt from the oil gauge, clean the internal cavity of the damping chamber of the oil gauge and the damping bolt from contamination; install a new sealing head gasket of the stilling bolt and screw the bolt back. It is allowed, if necessary, to lubricate the sealing gasket of the head of the stilling bolt with a thin layer of oil-resistant sealant KLT-75;

c) check the absence of plaque on the internal surfaces of the glass, which makes it difficult to visually control the oil level, mechanical damage in the form of cracks and chips; clean the “breathing” hole in the upper cover of the oil indicator with a soft wire;

d) blow out the oil gauges with compressed air at a pressure of no more than 2 kg/cm 2 to check the patency of the oil gauge with control by the air pressure coming out through the “breathing” hole;

If traces of oil leaks through the seals of the oil gauge, plaque on the inner surface of the glass, which makes it difficult to visually check the oil level, foreign particles (sealant residues, etc.) or other defects, the oil gauge is completely disassembled and the defects are eliminated with subsequent assembly. In this case, the resting bolt is screwed into place last, after the sealant that seals the glass has hardened. After assembly, the oil indicator is installed on the oil tank with the inspection hole of the small indicator housing in the direction opposite to the motor housing, after which the oil indicator is re-checked according to item d).

When installing the floorboards of the upper part of the body and the connecting jumpers between the floorboards, use sealant (paint) in the threaded connection of the jumpers as a countermeasure.

3.13 Technological map of the current repair of asynchronous electric motors 6kV (NR).

3.14 Technological map of the current repair of the backup exciter DAZ-18-10-6 (U3), GSP-2000-1000.

When replacing a bearing, it must be pressed off the shaft using a screw puller. The new bearing is washed from conservation grease in B-70 gasoline. Heat the bearing in an oil bath or with an inductor to a temperature of 90°C and press onto the shaft. Refer to Appendix 20 for bearing mounting recommendations. Shaft fit is tight. Then the bearing is filled with grease (LITOL-24, SVEM, TsIATIM-201). After assembly, make a control measurement of the motor insulation resistance and absorption coefficient with a 2500V megohmmeter. The insulation resistance must be at least 40 MΩ, the absorption coefficient must be at least the value specified in clause 1.3.2.

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The most difficult and responsible issue of repair of electric motors is to determine the suitability of serviceable windings for further operation and to establish the type and required amount of repair of faulty windings.

Determination of suitability of windings

Typical winding damages are insulation damage and electrical circuit integrity failure. The condition of the insulation is judged by such indicators as the insulation resistance, the results of the insulation test with increased voltage, the deviations of the DC resistance values ​​​​of individual windings (phases, poles, etc.) from each other, from previously measured values ​​\u200b\u200bor from factory data, as well as by the absence of signs of interturn short circuits in individual parts of the winding. In addition, the assessment takes into account the total duration of the electric motor without rewinding and its operating conditions.

Determination of the degree of wear of the insulation of the windings is carried out on the basis of various measurements, tests and assessment of the external state of the insulation. In some cases, winding insulation according to appearance and according to the test results, it has satisfactory results and the engine after repair is put into operation without its repair. However, after working for a short time, the machine fails due to insulation breakdown. Therefore, the assessment of the degree of wear of the machine insulation is a crucial moment in determining the suitability of the windings.

A sign of thermal aging of the insulation is its lack of elasticity, brittleness, tendency to cracking and fracture under rather weak mechanical stresses. The greatest aging is observed in places of increased heating, remote from the outer surfaces of the insulation. In this regard, to study the thermal wear of the winding insulation, it is necessary to open it locally to the full depth. For the study, select areas of a small area located in the areas of the greatest aging of the insulation, but available for reliable restoration of the insulation after opening. To ensure the reliability of the results of the study, there should be several places for opening the insulation.

At the opening, the insulation is examined in layers, repeatedly bending the removed sections and examining their surface through a magnifying glass. If necessary, compare identical samples of old and new insulation from the same material. If the insulation during such tests breaks, peels and multiple cracks form on it, then it must be replaced in whole or in part.

The signs of unreliable insulation are also the penetration of oil contaminants into the thickness of the insulation and the loose fitting of the winding in the groove, in which vibration movements of the conductors or sides of the sections (coils) are possible.

To determine the malfunction of the windings, use special devices. So, to detect turn short circuits and breaks in the windings of machines, to check the correct connection of the windings according to the scheme, to mark the output ends of the phase windings of electrical machines, the EL-1 electronic apparatus is used. It allows you to quickly and accurately detect a malfunction during the manufacture of windings, as well as after laying them in the grooves; the sensitivity of the device allows you to detect the presence of one short-circuited turn for every 2000 turns.

If only a small part of the windings has malfunctions and damages, then a partial repair is prescribed. However, in this case, it must be possible to remove the defective parts of the winding without damaging the healthy sections or coils. Otherwise more appropriate overhaul with complete winding replacement.

Repair of stator windings

Repair of stator windings is carried out in cases of insulation friction, short circuit between wires of different phases and between turns of one phase, short circuit of the winding to the housing, as well as breaks or poor contacts in the soldered joints of the windings or sections. The scope of repair depends on the general condition of the stator and the nature of the fault. After determining the stator malfunction, a partial repair is performed with the replacement of individual winding coils or a complete rewind is carried out.

In the stators of asynchronous motors with a power of up to 5 kW of a single series, single-layer random windings are used. The advantages of these windings are that the wires of one coil are laid in each half-closed slot, the laying of the coils in the slots is a simple operation, and the fill factor of the slot with wires is very high. In the stators of electrical machines with a power of 5-100 kW, two-layer loose windings are used with a half-closed groove shape. For asynchronous motors with power above 100 kW, the windings are made with coils of rectangular wire. Machine stators for voltages above 660 V windings are wound with wires rectangular section.

Rice. 103. Hinged template for winding coils:
1 - clamping nut; 2 - fixing bar; 3 - hinge bar.

The methods of manufacturing and laying in the grooves of the stators are different for windings of round or rectangular wires. Coils of round wire are wound on special templates. Manual winding of coils requires a lot of time and labor. More often, mechanized winding of coils is used on machines with special hinged templates (Fig. 103), with which coils of various sizes can be wound. The same templates allow you to wind all coils in series, designed for one coil group or for the entire phase.

The windings are made of wires of the PELBO brand (wire enameled with oil varnish and covered with one layer of cotton threads), PEL (wire enameled with oil-based varnish), PBD (wire insulated with two layers of cotton threads), PELLO (wire, insulated with oil varnish and one layer of lavsan threads).

Having wound the coil groups, they are tied up with tape and proceed to laying in the grooves. To isolate the windings from the housing in the slots, slot sleeves are used, which are a single-layer or multi-layer U-shaped bracket made of a material selected depending on the insulation class. So, for insulation class A, electric cardboard and varnished cloth are used, for heat-resistant winding - flexible micanite or glass micanite.

Production of insulation and laying soft loose winding of an asynchronous electric motor

The block diagram of the algorithm and the flow chart for the repair of the bulk winding of an asynchronous motor is shown below.

Winding technology:

1. Cut a set of strips of insulating material according to the dimensions of the winding data. Bend the cuff on the cut strips on both sides. Make a set of groove sleeves.


2. Clean the stator slots from dust and dirt. Insert the groove insulation to its full length in all grooves.


3. Cut a set of strips of insulating material and prepare the gaskets to size. Prepare a set of gaskets for the frontal parts of the windings.


4. Insert two plates into the groove to protect the wire insulation from damage when laying them. Insert a coil group into the stator bore; straighten the wires with your hands and put them into the grooves Remove the plate from the groove Distribute the wires evenly in the groove with a fiber rod. Insert an interlayer insulating gasket into the groove. Set the coil on the bottom of the groove with a hammer (hatchet) With a two-layer winding, place the second coil in the groove.


5. Use ready-made wedges made of plastic materials (PTEF films, etc.) or make wooden ones. Cut wooden blanks to the size of the winding data. Determine their relative humidity and dry to a relative humidity of 8%. Soak wooden wedges in drying oil and dry.


6. Insert the wedge into the groove and jam with a hammer.
   Cut off the ends of the wedges protruding from the ends of the stator with needle-nosed pliers, leaving 5-7 mm ends on each side. Cut off the protruding parts of the insulating gaskets.


7. Insert insulating spacers in the ends of the windings between adjacent coils of two groups of different phases laid side by side.
   Bend the frontal parts of the winding coils by 15-18 ° with hammer blows towards the outer diameter of the stator. Follow the smooth bending of the coil wires at the points where they exit the groove.

The procedure for manufacturing insulation and laying winding wires may be different. For example, the manufacture of slot sleeves, interlayer gaskets, the manufacture of wooden wedges can be carried out before laying the windings, and then the work order remains according to this scheme.

In winding manufacturing technology, some generalizations are made in detail.

Rice. 104. Laying and insulation of a two-layer stator winding of asynchronous motors:
slot (a) and frontal parts of the winding (b):
1 - wedge; 2, 5 - electric cardboard; 3 - fiberglass; 4 - cotton tape; 6 - cotton stocking.

Coils of a two-layer winding are placed (Fig. 104) in the grooves of the core in groups as they were wound on a template. Coils are stacked in the following sequence. The wires are distributed in one layer and put those sides of the coils that are adjacent to the groove. The other sides of the coils are inserted after the lower sides of the coils of all slots covered by the winding pitch are inserted. The following coils are laid simultaneously with the lower and upper sides with a gasket in the grooves between the upper and lower sides of the coils of insulating pads made of electrical cardboard, bent in the form of a bracket. Between the frontal parts of the windings, insulating gaskets made of varnished cloth or sheets of cardboard with pieces of varnished cloth glued to them are laid.

Rice. 105. Device for driving wedges into grooves

After laying the winding in the grooves, the edges of the groove sleeves are bent and wooden or textolite wedges are driven into the grooves. To protect the wedges 1 from breakage and protect the frontal part of the winding, a device (Fig. 105) is used, consisting of a bent sheet steel of the clip 2, into which a steel rod 3 is freely inserted, having the shape and size of a wedge. The wedge is inserted with one end into the groove, the other into the holder and driven by hammer blows on the steel rod. The length of the wedge should be 10 - 20 mm longer than the length of the core and 2 - 3 mm less than the length of the sleeve; wedge thickness - not less than 2 mm. The wedges are boiled in drying oil at a temperature of 120-140 C for 3-4 hours.

After the coils are laid in the grooves and the windings are wedged, the circuit is assembled, starting with the serial connection of the coils into coil groups. For the beginning of the phases, the conclusions of the coil groups coming out of the grooves located near the input shield of the electric motor are taken. The conclusions of each phase are connected, having previously stripped the ends of the wires.

Having assembled the winding circuit, they check the dielectric strength of the insulation between the phases and on the case. The absence of turn short circuits in the winding is determined using the EL-1 apparatus.

Replacing a coil with damaged insulation

The replacement of a coil with damaged insulation begins with the removal of the insulation of the inter-coil connections and bandages, which attach the front parts of the coils to the bandage rings, then the spacers between the front parts are removed, the coil connections are unsoldered and the slot wedges are knocked out. The coils are heated by direct current to a temperature of 80 - 90 °C. The upper sides of the coils are raised with the help of wooden wedges, carefully bending them inside the stator and tying them to the frontal parts of the stacked coils with a keeper tape. After that, the coil with damaged insulation is removed from the grooves. The old insulation is removed and replaced with a new one.

If, as a result of turn short circuits, the wires of the coil are burned out, it is replaced with a new one wound from the same wire. When repairing windings from rigid coils, it is possible to save winding wires of rectangular cross section for restoration.

The technology of winding rigid coils is much more complicated than random winding coils. The wire is wound on a flat template, the grooved parts of the coils are stretched to an equal distance between the grooves. Coils have considerable elasticity, therefore, to obtain accurate dimensions, their grooved parts are pressed, and the frontal parts are straightened. The pressing process consists in heating coils lubricated with bakelite or glyptal varnish under pressure. When heated, the binders soften and fill the pores of the insulating materials, and after cooling, they harden and hold the wires of the coils together.

Before laying in the grooves, the coils are straightened with the help of devices. The finished coils are placed in grooves, heated to a temperature of 75 - 90 ° C and upset with light hammer blows on a wooden sedimentary plank. The frontal parts of the coils are also straightened. The lower sides of the frontal parts are tied to the bandage rings with a cord. Gaskets are clogged between the frontal parts. The prepared coils are lowered into the grooves, the grooves are wedged and the inter-coil connections are connected by soldering.

Repair of rotor windings

In asynchronous motors, the following types of windings are used: "squirrel cages" with rods filled with aluminum or welded from copper rods, coil and rod. The most widespread are "squirrel cages" filled with aluminum. The winding consists of rods and closing rings on which fan wings are molded.

To remove the damaged “cell”, melt it or dissolve aluminum in a 50% solution of caustic soda for 2–3 hours. A new “cell” is poured with molten aluminum at a temperature of 750–780 °C. The rotor is preheated to 400-500 °C to avoid premature solidification of aluminum. If the rotor is weakly pressed before pouring, then during pouring aluminum can penetrate between the iron sheets and close them, increasing the losses in the rotor from eddy currents. Too strong pressing of iron is also unacceptable, since breaks of newly poured rods may occur.

Repair of "squirrel cages" from copper rods is most often carried out using old rods. After sawing the connections of the “cage” rods on one side of the rotor, the ring is removed, and then the same operation is performed on the other side of the rotor. Mark the position of the ring relative to the grooves so that the ends of the rods and the old grooves coincide during assembly. The rods are knocked out by carefully hitting the aluminum tamps with a hammer and straightened.

The rods should enter the grooves with a light hammer blow on the textolite lining. It is recommended to simultaneously insert all the rods into the grooves and knock out the diametrically opposite rods. The rods are soldered in turn, preheating the ring to a temperature at which the copper-phosphorus solder easily melts when brought to the junction. When soldering, they monitor the filling of the gaps between the ring and the rod.

In asynchronous motors with a phase rotor, the methods for manufacturing and repairing rotor windings are not much different from the methods for manufacturing and repairing stator windings. The repair begins with the removal of the winding circuit, the locations of the beginning and ends of the phases on the rotor and the location of the connections between the coil groups are fixed. In addition, sketch or record the number and location of bandages, the diameter of the bandage wire and the number of locks; number and location of balancing weights; insulation material, the number of layers on the rods, gaskets in the groove, in the frontal parts, etc. Changing the connection diagram during the repair process can lead to rotor imbalance. A slight imbalance while maintaining the circuit after repair is eliminated by balancing weights that are attached to the winding holders of the rotor winding.

After establishing the causes and nature of the malfunction, the issue of partial or complete rewinding of the rotor is decided. The bandage wire is unwound onto a drum. After removing the bandages, the solderings in the heads are unsoldered and the connecting clamps are removed. The frontal parts of the rods of the upper layer are bent from the side of the contact rings and these rods are taken out of the groove. Clean the rods from the old insulation and straighten them. The grooves of the rotor core and the winding holder are cleaned of insulation residues. Straightened rods are isolated, impregnated with varnish and dried. The ends of the rods are tinned with POS-ZO solder. The groove insulation is replaced with a new one, laying the boxes and gaskets on the bottom of the grooves with a uniform projection from the grooves on both sides of the core. After graduation preparatory work start assembling the rotor windings.

Rice. 106. Laying the coil of the rotor winding:
a - coil; b - an open groove of the rotor with a laid winding.

In a single series A of asynchronous motors with a power of up to 100 kW with a phase rotor, loop two-layer rotor windings from multi-turn coils are used (Fig. 106, a).

When repairing, the windings are put into open grooves (Fig. 106, b). The previously removed rods of the rotor windings are also used. The old insulation is removed from them and new insulation is applied. In this case, the assembly of the winding consists of placing the rods in the slots of the rotor, bending the front part of the rods and connecting the rods of the upper and bottom rows soldering or welding.

After laying all the rods or finished windings, temporary bandages are applied to the rods, they are tested for the absence of a short circuit to the case; the rotor is dried at a temperature of 80-100 ° C in drying cabinet or stoves. After drying, the winding insulation is tested, the rods are connected, the wedges are driven into the grooves and the windings are bandaged.

Often in repair practice, bandages are made of fiberglass and baked together with the winding. The cross section of the fiberglass bandage is increased by a factor of 2 to 3 in relation to the section of the wire bandage. The fastening of the end coil of fiberglass with the underlying layer occurs during the drying of the winding during sintering of the thermosetting varnish with which the fiberglass is impregnated. With this design of the bandage, such elements as locks, brackets and under bandage insulations disappear. Devices and machines for winding fiberglass bandages use the same as for winding wire.

Repair of anchor windings

Faults in the windings of the armatures of DC machines can be in the form of a connection between the winding and the housing, interturn short circuits, wire breaks, and soldering of the ends of the winding from the collector plates.

To repair the winding, the armature is cleaned of dirt and oil, the bandages are removed, the connections to the collector are unsoldered and the old winding is removed. To facilitate the removal of the winding from the grooves, the armature is heated at a temperature of 80 - 90 ° C for 1 hour. To lift the upper sections of the coils, a polished wedge is driven into the groove between the coils, and to lift the lower sides of the coils - between the coil and the bottom of the groove. The grooves are cleaned and covered with insulating varnish.

In the armatures of machines with a power of up to 15 kW with a semi-closed groove shape, bulk windings are used, and for machines of higher power with an open groove shape, coil windings are used. Coils are made of round or rectangular wire. The most widely used template armature windings are made of insulated wires or copper bars isolated with varnished cloth or mica tape.

Sections of the template winding are wound on a universal template in the form of a boat and then stretched, since it must lie in two grooves located around the circumference of the armature. After giving the final shape, the coil is insulated with several layers of tape, impregnated twice in insulating varnishes, dried and tinned the ends of the wires for subsequent soldering in the collector plates.

An insulated coil is inserted into the grooves of the armature core. They are fixed in them with special wedges and the wires are attached to the collector plates by soldering with POS-30 solder. Wedges are pressed from heat-resistant plastic materials - isoflex-2, trivolterm, PTEF films (polyethylene terephthalate).

The connection of the ends of the winding by soldering is carried out very carefully, since poor-quality soldering will lead to a local increase in resistance and an increase in the heating of the connection during operation of the machine. The quality of the soldering is checked by inspecting the soldering point and measuring the contact resistance, which should be the same between all pairs of collector plates. Then the operating current is passed through the armature winding for 30 minutes. In the absence of defects in the joints, there should be no increased local heating.

All work on the dismantling of bandages, the application of bandages made of wire or glass tape on the anchors of DC machines is carried out in the same manner as when repairing the windings of phase rotors of asynchronous machines.

Repair of pole coils

Pole coils are called excitation windings, which are divided by purpose into coils of the main and additional poles of DC machines. The main parallel excitation coils consist of many turns of thin wire, while the series excitation coils have a small number of turns of heavy gauge wire wound from bare copper bars laid flat or edgewise.

After determining the faulty coil, it is replaced by assembling the coil at the poles. New pole coils are wound on special machines using frames or templates. Pole coils are made by winding insulated wire directly onto an insulated pole, previously cleaned and coated with glyptal varnish. A varnished cloth is glued to the pole and wrapped with several layers of micafolium impregnated with asbestos varnish. After winding, each layer of micafolium is ironed with a hot iron and wiped with a clean cloth. A layer of varnished cloth is glued onto the last layer of micafolium. Having insulated the pole, put on the lower insulating washer, wind the coil, put on the upper insulating washer and wedge the coil on the pole with wooden wedges.

Coils of additional poles are repaired, restoring the insulation of the turns. The coil is cleaned of old insulation, put on a special mandrel. The insulating material is asbestos paper 0.3 mm thick, cut in the form of frames according to the size of the turns. The number of spacers must be equal to the number of turns. On both sides they are covered with a thin layer of bakelite or glyptal varnish. The turns of the coil are moved apart on the mandrel and spacers are inserted between them. Then the coil is pulled together with a cotton tape and pressed. The coil is pressed on a metal mandrel, on which an insulating washer is put on, then the coil is installed, covered with a second washer and the coil is compressed. Heating by means of a welding transformer up to 120 C, the coil is additionally compressed. Cool it in the pressed position to 25 - 30 °C. After removal from the mandrel, the coil is cooled, coated with air-drying varnish and kept at a temperature of 20–25 °C for 10–12 hours.

Rice. 107. Options for insulation of pole cores and pole coils:
1, 2, 4 - getinaks; 3 - cotton tape; 5 - electric cardboard; 6 - textolite.

The outer surface of the coil is insulated (Fig. 107) alternately with asbestos and micanite tapes, fixed with taffeta tape, which is then varnished. The coil is mounted on an additional pole and wedged with wooden wedges.

Drying, impregnation and testing of windings

Manufactured windings of stators, rotors and armatures are dried in special ovens and drying chambers at a temperature of 105-120 °C. By drying, moisture is removed from hygroscopic insulating materials (electrocardboard, cotton tapes), which prevents deep penetration of impregnating varnishes into the pores of insulating parts during impregnation of the winding.

Drying is carried out in infrared rays of special electric lamps, or using hot air in drying chambers. After drying, the windings are impregnated with varnishes BT-987, BT-95, BT-99, GF-95 in special impregnating baths. The premises are equipped with supply and exhaust ventilation. Impregnation is carried out in a bath filled with varnish and equipped with heating for better penetration of the varnish into the insulation of the wire winding.

Over time, the varnish in the bath becomes more viscous and thicker, due to the volatilization of varnish solvents. As a result, their ability to penetrate into the insulation of the winding wires is greatly reduced, especially in cases where the winding wires are tightly packed into the grooves of the cores. Therefore, when impregnating the windings, the density and viscosity of the impregnating varnish in the bath are constantly checked and solvents are periodically added. The windings are impregnated up to three times, depending on their operating conditions.

Rice. 108. Device for impregnation of stators:
1 - tank; 2 - pipe; 3 - branch pipe; 4 - stator; 5 - cover; 6 - cylinder; 7 - rotary traverse; 8 - column.

To save varnish, which is consumed due to sticking to the walls of the stator frame, another method is used to impregnate the winding using a special device (Fig. 108). Ready for impregnation, the stator with winding 4 is installed on the lid of a special tank 1 with varnish, having previously closed the stator terminal box with a plug. A seal is laid between the end of the stator and the tank cover. In the center of the cover there is a pipe 2, the lower end of which is located below the level of varnish in the tank.

To impregnate the stator winding, compressed air is supplied to the tank through pipe 3 with a pressure of 0.45 - 0.5 MPa, with which the varnish level rises to fill the entire winding, but below the upper edge of the stator frame. At the end of the impregnation, turn off the air supply and hold the stator for about 40 minutes (to drain the remaining varnish into the tank), remove the plug from the terminal box. After that, the stator is sent to the drying chamber.

The same device is also used to impregnate the stator windings under pressure. The need for this arises in cases where the wires are very tightly laid in the stator grooves and during normal impregnation (without varnish pressure), the varnish does not penetrate into all the pores of the insulation of the turns. The pressure impregnation process is as follows. Stator 4 is installed in the same way as in the first case, but is closed from above by cover 5. Compressed air is supplied to tank 1 and cylinder b, which presses cover 5 to the end of the stator frame through the installed seal gasket. Rotary traverse 7, mounted on column 8, and the screw connection of the cover with the cylinder make it possible to use this device for impregnating stator windings of various heights.

The impregnating varnish is supplied to the tank from a container located in another, non-flammable room. Lacquer and solvents are toxic and flammable and, in accordance with labor protection rules, work with them should be carried out in goggles, gloves, rubber apron in rooms equipped with supply and exhaust ventilation.

After impregnation, the windings of the machines are dried in special chambers. The air supplied to the chamber by forced circulation is heated by electric heaters, gas or steam heaters. During the drying of the windings, the temperature in the drying chamber and the temperature of the air leaving the chamber are continuously monitored. At the beginning of the drying of the windings, the temperature in the chamber is slightly lower (100-110 °C). At this temperature, solvents are removed from the insulation of the windings and the second drying period begins - baking of the varnish film. At this time, the drying temperature of the windings is increased to 140 ° C for 5-6 hours (for insulation class L). If after several hours of drying the insulation resistance of the windings remains insufficient, then the heating is turned off and the windings are allowed to cool to a temperature 10-15 ° C higher than the ambient temperature, after which the heating is turned on again and the drying process continues.

The processes of impregnation and drying of windings at power repair enterprises are combined and, as a rule, mechanized.

In the process of manufacturing and repairing the windings of machines, the necessary tests of the insulation of the coils are carried out. The test voltage should be such that during the test defective sections of the insulation are revealed and the insulation of good windings is not damaged. So, for coils with a voltage of 400 V, the test voltage of a coil not dismantled from the grooves for 1 min should be 1600 V, and after connecting the circuit during partial repair of the winding - 1300 V.

The insulation resistance of the windings of electric motors with voltage up to 500 V after impregnation and drying must be at least 3 MΩ for the stator windings and 2 MΩ for the rotor windings after full rewinding and 1 MΩ and 0.5 MΩ, respectively, after partial rewinding. These winding insulation resistance values ​​are recommended based on the practice of repair and operation of repaired electrical machines.