Technological map for connecting an asynchronous motor. Maintenance and overhaul of an asynchronous motor. Installation and dismantling of equipment should be carried out by specialized teams of the enterprise or specialized commissioning

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 All-Union State All-Union Order of the Red Banner of Labor Research Institute for the Repair and Operation of the Machine and Tractor Fleet (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 that list the numbers and content of all technological operations, technical conditions and instructions for carrying out repairs, provide 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 the 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 map, which contains information about the customer, the technical characteristics of the 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 grooves, information about the winding data before repair and according to the calculation , information about the mechanical part - its condition, information about the control of windings and bench tests.
The technological map is signed by a troubleshooting technician, a foreman, a calculation engineer and QCD employees.
The drying officer fills in the drying logs of electrical machines, which include: the customer, order number, passport data of the machine, drying place, 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 passport data, data of the HV and LV windings and the dimensions of the magnetic circuit, but also the mass of oil, the removable part and the total mass of the 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 winding resistance 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 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 the 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
Fault detection 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:
breakage of the electrical 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 one 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, as mentioned above, they 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 given preference, 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 an electric machine with stator steel packages and winding is installed on a lathe or milling machine and a 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 package pressing 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.
With the thermochemical method of winding removal, an electric 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 with clean air, depressurizing and opening the container, removing 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 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.

According to the design, the windings of electrical machines are divided into three types: concentric, loose and template. The latter, in turn, are subdivided 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; preparing 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 greater, the greater the 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 current 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 interference), 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 of turning (on a lathe or in our own bearings), chipping, grinding and polishing. The cutting of the collector (using a cutter on the machine, a hacksaw blade or a special scraper) is performed with 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 disassembling and especially for assembling 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-circuiting mechanism consists in restoring the worn side ribs of the short-circuiting 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 made of various materials are restored using manual arc and gas surfacing and welding, automatic surfacing and submerged arc welding, 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 and in a liquid medium, plating, steeling, 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 seats for bearings 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 electrolyte 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 of 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.

Dismantling is the dismemberment of an electrical machine into separate parts and assemblies. The most important task is to carry it out in such a way as to prevent additional damage to the machines and their components.

To do this, before disassembly, in particular, in case of severe corrosion of fasteners, all bolts, nuts and joints are lubricated with transformer or machine oil. Sometimes it is advisable to apply rags moistened with oils or kerosene, other organic solvents to them. The exposure time of the solvent is determined by experience; if the gank or screw is not turned, it is prolonged.

Figure 6. The sequence of disassembly of an asynchronous motor type 4A (power up to 10 kW)

The order of disassembly, the tools and tools used depend on the type of machine, its power and design features. For an asynchronous motor of the 4A series with a power of up to 10 kW with a squirrel-cage rotor, a closed, ventilated version, the disassembly procedure is as follows:

The fan cover 2 is removed (Fig. 6. a) To do this, the screws fastening it to the machine body are unscrewed

Fan 1 is removed, while the spring ring is removed from the shaft groove. For removal, there are often special threaded holes in the steel fan sleeve

Fasteners are removed, bearing caps are removed 3.

The rear bearing shield 5 is removed (Fig. 6, b). located on the side of the removed fan.

To remove (after removing the shield fastening bolts), with light hammer blows made of soft material (wood, aluminum, etc.) along the edge of the part, move the shield away from the housing along the shaft. In this case, the rotor shaft is held by hand or with a device on weight to prevent it from falling onto the stator, otherwise the sheets of steel of the magnetic circuit can be damaged. You can use a regular hammer. but in this case it is necessary to use soft pads. Often, when performing such work, special devices are used. such as a universal screw extractor (fig. 7) or a hydraulic mobile extractor, etc.

1- emphasis; 2 - screw; 3 - capture; 4 - handle

Figure 7- Universal screw extractor.

The front shield 4 is removed (located on the drive side), and the fastening bolts are also preliminarily removed (Fig. 7. c). Usually it is separated together with rotor 6. However, often the last one, after removing the bearing shields, remains in the stator bore, then a special operation is performed to remove the rotor (Fig. 7, c). By weight, the rotors are divided into micro (0.01-0.1 kg), small (0.1-3 kg), medium (3-1000 kg).

When removing the rotor, care must be taken not to damage the frontal parts of the winding, the fan wings (on the squirrel cage), the magnetic circuit and other parts. The withdrawal of the rotor from the stator is one of the most critical operations, the slightest negligence leads to serious damage (violations of the insulation of current-carrying parts, damage to the magnetic circuit, etc.) Small rotors are removed manually by placing an electric cardboard in the air gap, or using wooden supports under the shaft. Medium and large - with the help of devices of various designs (depending on the design and weight of the rotor), for example, as in fig. eight.

Figure 8 - Pulling out the rotor with

It is permissible to remove the rotor when removing the front shield. But once again we emphasize that you should carefully monitor to prevent damage to other parts of the machine during this operation.

Usually, ball bearings (8) remain on the rotor shaft and are removed from it by pullers only in cases of their replacement or repair of rotor parts (Fig. 7, d).

For asynchronous electric motors with a phase rotor, when removing the rear shield (located on the side of the slip rings), first remove the casing, then remove the brushes and, finally, unscrewing the fixing bolts, remove the body of the rings. At the same time, the connecting clamps are soldered from the output ends. Removal and disassembly of slip rings is performed only in case of their repair in the same way as collectors of DC machines.

When disassembling units, the parts of which are connected with a large interference (bearing with a shaft, etc.), if the shooting causes a "seizure" of the metal at the seat, the parts are heated, for example, by pouring hot oil on the removed part. Some repair companies use induction heating installations for this purpose. The magnetic flux, passing through the mounted part, heats it up with eddy currents. After disassembling the electrical machine, its parts and assemblies are cleaned or washed.

Current repairs are carried out to ensure and restore the efficiency of the electric motor. It consists in replacing or restoring individual parts. Carried out at the installation site of the machine or in the workshop.

The frequency of current repairs of electric motors is determined by the PPR system. It depends on the location of the engine, the type of machine or machine in which it is used, as well as the duration of work per day. Electric motors are subject to current repairs mainly once every 24 months.
When carrying out current repairs, the following operations are performed: cleaning, dismantling, disassembly and fault detection of the electric motor, replacement of bearings, repair of terminals, terminal box, damaged sections of the frontal parts of the winding, assembly of the electric motor, painting, idling and under load testing. For DC machines and electric motors with a phase rotor, the brush-collector mechanism is additionally repaired.

Table 1 Possible malfunctions of electric motors and their causes

Current repairs are carried out in a certain technological sequence. Before starting the repair, it is necessary to review the documentation, determine the operating time of the motor bearings, and establish the presence of unrepaired defects. A foreman is appointed to carry out the work, the necessary tools, materials, devices, in particular, lifting mechanisms, are prepared.

Before starting dismantling, the electric motor is disconnected from the network, measures are taken to prevent accidental voltage supply. The machine to be repaired is cleaned of dust and dirt with brushes, blown with compressed air from the compressor. Unscrew the screws securing the terminal box cover, remove the cover and disconnect the cable (wires) supplying power to the motor. The cable is removed, observing the required bending radius so as not to damage it. Bolts and other small parts are placed in a box that is included in the tool kit.

When dismantling the electric motor, it is necessary to make marks with a core to fix the position of the coupling halves relative to each other, and also to note which hole in the coupling half the pin enters. The pads under the paws should be tied and marked so that after repair each group of pads should be installed in its place, this will facilitate the centering of the electric machine. Covers, flanges and other details should also be marked. Failure to follow this rule may result in the need for re-disassembly.

Remove the electric motor from the foundation or workplace by the eyebolts. A shaft or endshield must not be used for this purpose. Lifting devices are used for removal.

Disassembly of the electric motor is carried out in compliance with certain rules. It begins with the removal of the coupling half from the shaft. In this case, manual and hydraulic pullers are used. Then the fan casing and the fan itself are removed, the bearing shield mounting bolts are unscrewed, the rear bearing shield is removed with light hammer blows on the wood, copper, aluminum extension, the rotor is removed from the stator, the front bearing shield is removed, the bearings are dismantled.

After disassembly, the parts are cleaned with compressed air using a hair brush for the windings and a metal brush for the casing, end shields, and frame. Dried dirt is removed with a wooden spatula. Do not use a screwdriver, knife or other sharp objects. Detection of an electric motor involves an assessment of its technical condition and the identification of faulty components and parts.

When defecting the mechanical part, the following is checked: the condition of the fasteners, the absence of cracks in the housing and covers, the wear of the bearing seats and the condition of the bearings themselves. In DC machines, a serious node that is subject to comprehensive consideration is the brush-collector mechanism.

Here, damage to the brush holder, cracks and chips on the brushes, wear of the brushes, scratches and dents on the surface of the collector, and the protrusion of micanite gaskets between the plates are observed. Most of the malfunctions of the brush-collector mechanism are eliminated during current repairs. In case of serious damage to this mechanism, the machine is sent for overhaul.

Malfunctions of the electrical part are hidden from the human eye, it is more difficult to detect them, special equipment is needed. The number of damages to the stator winding is limited by the following defects: open circuit, short circuit of individual circuits between themselves or on the housing, coil short circuits.

A break in the winding and a short circuit to the case can be detected using a megohmmeter. Turn circuits are determined using the EL-15 apparatus. A break in the rods of a squirrel-cage rotor is found on a special installation. Malfunctions eliminated during current repairs (damage to the frontal parts, breakage or burning of the lead ends) can be determined with a megohmmeter or visually, in some cases an EL-15 device is required. During fault detection, the insulation resistance is measured to determine the need for drying.

Directly current repair of the electric motor is as follows. When the thread is broken, a new one is cut (for further operation, a thread with no more than two cut threads is allowed), the bolts are replaced, the cover is welded. Damaged winding leads are covered with several layers of insulating tape or replaced if their insulation along the entire length has cracks, delaminations or mechanical damage.

In case of violation of the frontal parts of the stator winding, air-drying varnish is applied to the defective area. Bearings are replaced with new ones if there are cracks, chips, dents, discoloration and other malfunctions. The landing of the bearing on the shaft is usually carried out by preheating it to 80...90°C in an oil bath.

The installation of bearings is carried out manually using special cartridges and a hammer or mechanized using a pneumohydraulic press. it was possible to replace them with new ones.

The order of assembly of the electric motor depends on its size and design features. For electric motors of sizes 1 - 4, after pressing the bearing, the front end shield is installed, the rotor is inserted into the stator, the rear end shield is put on, the fan and cover are put on and fastened, after that the coupling half is installed. Further, according to the scope of the current repair, idling, articulation with a working machine and a load test are carried out.

Checking the operation of the electric motor at idle or with an unloaded mechanism is carried out as follows. After checking the operation of protection and signaling, a test run is performed with listening to knocking, noise, vibrations and subsequent shutdown. Then the electric motor is started, the acceleration to the rated speed and the heating of the bearings are checked, the no-load current of all phases is measured.

The no-load current values ​​measured in the individual phases must not differ from each other by more than ±5%. A difference between them of more than 5% indicates a malfunction of the stator or rotor winding, a change in the air gap between the stator and the rotor, and a bearing failure. The duration of the check is usually at least 1 hour. The operation of the electric motor under load is carried out when the process equipment is turned on.

Post-repair testing of electric motors in accordance with the current Norms should include two checks - measurement of insulation resistance and operability of protection. For electric motors up to 3 kW, the insulation resistance of the stator winding is measured, and for motors over 3 kW, additionally. In this case, for electric motors with voltage up to 660 V in the cold state, the insulation resistance must be at least 1 MΩ, and at a temperature of 60 ° C - 0.5 MΩ. Measurements are made with a megohmmeter at 1000 V.

Checking the operation of machine protection up to 1000 V with a power system with a grounded neutral is carried out by directly measuring the current of a single-phase short circuit to the case using special instruments or by measuring the impedance of the "phase - zero" loop, followed by determining the current of a single-phase short circuit. The received current is compared with the rated current of the protective device, taking into account the PUE coefficients. It must be greater than the fuse current of the nearest fuse or circuit breaker release.

In the process of performing current repairs, it is recommended to carry out modernization measures to improve the reliability of electric motors of old modifications. The simplest of them is the triple impregnation of the stator winding with varnish with the addition of an inhibitor. The inhibitor, diffusing into the lacquer film and filling it, prevents the penetration of moisture. It is also possible to encapsulate the frontal parts with epoxy resins, but in this case the electric motor may become unrepairable.

Filling out the technological card for the repair of the mechanical part of the electric motor

Task: Draw up a technological map for the repair of the mechanical part of the electric motor according to the model of table 1. Draw up a map separately for the repair of cores, housings and end shields, and the repair of shafts.

1) Study the theoretical material on the repair of the mechanical part of the electric motor, using the training manual, Installation, maintenance and repair of electrical and electromechanical equipment, §§ 9.1; 9.2;.9.3. (provided by the teacher).

Table 1. Technological map of the repair of the mechanical part of the electric motor

AC motor

The purpose of the work: mastering the ability to fill out the routing and technological documentation for the repair of the mechanical part of the electric motor

Task: Make a table of the sequence of disassembly and assembly of an AC motor according to the model of table 1.

1) Study the theoretical material on the disassembly and assembly of an AC motor, using the study guide, Installation, maintenance and repair of electrical and electromechanical equipment, §§ 8.3., 10.5. (provided by the teacher).

Practical Work Instruction Card No. 28

Description of the disassembly and assembly sequence

DC motor

The purpose of the work: mastering the ability to fill out the routing and technological documentation for the repair of the mechanical part of the electric motor

Task: Make a table of the sequence of disassembly and assembly of a DC motor according to the model of table 1.

1) Study the theoretical material on disassembling and assembling a DC motor using the study guide, Installation, maintenance and repair of electrical and electromechanical equipment, §§ 8.3., 10.5. (provided by the teacher).

2) Fill in the columns of table 1. separately for disassembly and assembly.

Table 1. The sequence of disassembly and assembly of the AC motor

Practical Work Instruction Card No. 29

Filling in the winding repair flow chart

The purpose of the work: mastering the ability to fill out the routing and technological documentation for the repair of the winding of an AC electric motor

Task: Draw up a technological map for repairing the winding of an AC electric motor according to the model of table 1. Draw up a map separately for repairing windings from round and rectangular wires.

1) Study the theoretical material on the repair of the mechanical part of the electric motor, using the training manual, Installation, maintenance and repair of electrical and electromechanical equipment, §§ 10.1 .; 10.2 (provided by the teacher).

2) Fill in the technological map according to table 1. Each operation should contain no more than one action. If there is more than one variant of the operation, describe each variant, indicating in the column "Description of the operation" in which cases it is performed.

AC electric motor

Practical Work Instruction Card No. 30

Filling out the DC motor repair worksheet

The purpose of the work: mastering the ability to fill out the routing and technological documentation for the repair of a DC electric motor

Task: Draw up a technological map for the repair of a DC motor according to the model of table 1. Draw up a map separately for the repair of the armature, pole windings.

1) Study the theoretical material on the repair of a DC motor using the study guide, Installation, maintenance and repair of electrical and electromechanical equipment, § 84 (provided by the teacher).

2) Fill in the technological map according to table 1. Each operation should contain no more than one action. If there is more than one variant of the operation, describe each variant, indicating in the column "Description of the operation" in which cases it is performed.

Table 1. Technological map of DC motor repair

Practical work instruction card No. 31

Filling in the flow chart for the repair of ballasts

The purpose of the work: mastering the ability to fill in the route-technological documentation for the repair of ballasts

Task: Draw up a flow chart for the repair of ballasts according to the model of table 1.

1) Study the theoretical material on the repair of ballasts using the training manual, Installation, maintenance and repair of electrical and electromechanical equipment, § 14.4. (provided by the teacher).

2) Fill in the technological map according to table 1. Each operation should contain no more than one action. If there is more than one variant of the operation, describe each variant, indicating in the column "Description of the operation" in which cases it is performed.

Table 1. Technological map of winding repair

AC electric motor

Technological (map) process during the repair of a high-voltage synchronous electric motor weighing 2 tons. Attire, shutdown of the electric motor, withdrawal for repair, use of lifting mechanisms, slinging scheme, rigging to the repair site

Architecture, design and construction

If work on the electric motor or the mechanism driven by it is connected with touching the current-carrying and rotating parts, the electric motor must be turned off with the implementation of the provided technical measures to prevent its erroneous switching on. Work not related to touching the current-carrying or rotating parts of the electric motor and the mechanism driven by it can be performed on a running electric motor. When working on an electric motor, it is allowed to install grounding on any section of the cable line ...

Technological (map) process during the repair of a high-voltage synchronous electric motor weighing 2 tons. Attire, shutdown of the electric motor, withdrawal for repair, use of lifting mechanisms, slinging scheme, rigging to the repair site.

If the work on the electric motor or the mechanism driven by it is connected with touching the current-carrying and rotating parts, the electric motor must be turned off with the implementation of the provided technical measures to prevent its erroneous switching on. In this case, for a two-speed electric motor, both power circuits of the stator windings must be disconnected and disassembled.

Work that is not related to touching the current-carrying or rotating parts of the electric motor and the mechanism driven by it can be carried out on a running electric motor.

It is not allowed to remove the guards of the rotating parts of the operating electric motor and mechanism.

When working on an electric motor, it is allowed to install grounding on any section of the cable line connecting the electric motor to the switchgear section, shield, assembly. If work on the electric motor is designed for a long period of time, is not performed or is interrupted for several days, then the cable line disconnected from it must also be grounded on the side of the electric motor. In cases where the cross section of the cable cores does not allow the use of portable grounding, for electric motors with voltages up to 1000 V, it is allowed to ground the cable line with a copper conductor with a cross section of at least the cross section of the cable core, or to connect the cable cores to each other and insulate them. Such grounding or connection of cable cores should be taken into account in operational documentation on a par with portable grounding.

Before admission to work on electric motors capable of rotation due to the mechanisms connected to them (smoke exhausters, fans, pumps, etc.), the handwheels of stop valves (gate valves, valves, gate valves, etc.) must be locked. In addition, measures have been taken to slow down the rotors of electric motors or disengage the couplings.

The necessary operations with shutoff valves must be agreed with the shift supervisor of the technological workshop, section with an entry in the operational log.

Voltage must be removed from the circuits of manual remote and automatic control of electric drives of shut-off valves, guide vanes. Posters "Don `t open! People are working", and on the keys, buttons for controlling the electric drives of the shutoff valves - “Do not turn on! People are working". On electric motors of the same type or similar in size, installed next to the engine on which the work is to be performed, posters should be postedStop! Voltage"whether they are running or stopped.

Admission to all pre-prepared workplaces, one at a time on electric motors of the same voltage, is allowed to be performed simultaneously, transferring from one workplace to another is not required. At the same time, testing or putting into operation any of the electric motors listed in the work order until the work is completed on others is not allowed.

The procedure for turning on the electric motor for testing should be as follows:the foreman removes the team from the place of work, draws up the end of work and hands over the work order to the operational personnel;

operational personnel removes the installed grounding, posters, assembles the circuit.

After testing, if it is necessary to continue working on the electric motor, the operational personnel again prepares the workplace and the team, along with it, is again allowed to work on the electric motor.

Work on a rotating electric motor without contact with current-carrying and rotating parts can be carried out by order.

Maintenance of the brush apparatus with the motor running is allowed by order of a group III worker trained for this purpose, subject to the following precautions:

work with the use of face and eye protection, in buttoned overalls, being careful not to capture it by the rotating parts of the electric motor;

use dielectric galoshes, carpets;

do not touch the current-carrying parts of two poles or the current-carrying and grounding parts at the same time.

The rotor rings may only be ground while the motor is rotating with pads made of insulating material.

The labor protection instructions of the relevant organizations should set out in detail the requirements for preparing the workplace and organizing safe work on electric motors, taking into account the types of electric machines used, the features of ballasts, the specifics of mechanisms, technological schemes, etc.

Organizational measures that ensure the safety of work in electrical installations are:

registration of work by an order, order or list of works performed in the order of current operation;

work permit;

supervision during work;

registration of a break in work, transfer to another place, completion of work.

Responsible for the safe conduct of work are:

issuing the order, giving the order, approving the list of works performed in the order of current operation;

responsible work manager;

allowing;

work producer;

watching;

brigade members.