In the motor repair, if a reasonable repair method is adopted, the repair can get twice the result with half the effort. The problems that are often encountered in motor repair are summarized, and several practical methods in repair work are introduced. Reasonable use to get twice the result with half the effort. Several practical methods in motor repair Various situations will be encountered in the repair of the motor. If a reasonable repair method is adopted, detours can be avoided during the repair and the effect will be doubled with half the effort. The experience and experience in daily maintenance work are summarized into several practical methods for motor repair, mainly including the reduction of motor insulation resistance, the grounding point in the stator winding slot, the short circuit between winding turns, the cage rotor broken bar, and the parallel connection between the motors. The methods of handling and repairing problems such as the "fire of the headgear", the removal of old windings, the wear and tear of the rotor journal and the end cover bearing chamber are for reference. The problems that are often encountered in motor repair are summarized, and several practical methods in repair work are introduced. 1 After the end cover is installed, the treatment of the insulation resistance of the motor is reduced When repairing cage motors, the windings are well insulated to the casing before the end covers are installed. After installation, the insulation resistance decreases. This phenomenon can be judged that the fault occurs at both ends of the winding. The reason for the decrease in insulation resistance may be that the paint film on the enameled wire is partially broken or the winding mode is biased to cause the winding end to extend longer. After the end cover is covered, the inner wall of the end cover is close to or in contact with the fault point, so the winding insulation resistance is reduced. To eliminate this kind of fault, first determine which end of the motor the fault is. The judgment method is: first install a head end cover, and measure the insulation resistance of the winding with a 500V insulation resistance meter. If it is very low, it means that the winding at this end is faulty. Then, remove this end cap and install the other end cap to measure the insulation resistance of the winding. If it is also low, it means that there is also a fault at the other end. In the process of disassembling and assembling the end cover, the rotor may not be installed. After determining the fault end, generally reshape the winding end and apply some insulating paint. If the problem is not solved, a layer of thin film green paper can be placed on the outside of the winding end to easily contact the inner side of the end cover. Generally can be eliminated. 2 Find and deal with the grounding point in the stator winding slot The grounding in the stator winding slot generally occurs in the slot. Because the slot insulation paper is offset or damaged at the slot, or the slot is underlined or scribed carelessly, the enameled wire is placed under the slot insulation paper, or the slot insulation paper is squeezed when the slot is driven into the slot. Cause a ground fault. For this kind of fault, first determine whether the motor winding is damp, if it is damp, bake the motor, and the result is invalid, then it is judged that there is a ground fault. There are several ways to find the grounding point: Carefully inspect the lead wires and both ends of the slot, and found that the lead wires are intact, and the insulation of the slots at both ends of the slot is not damaged. The inside and outside of the motor are clean, and there is no dust and oil everywhere. This shows that the grounding point is in the slot. Untie the Y-shaped connection point of the stator winding, measure the insulation resistance of each phase to the ground, and find out the phase with the ground fault. Use a single-phase voltage regulator, the phase wire of its output end is connected to the lead wire of one end of the ground fault phase, the neutral wire is connected to the motor casing, and then the voltage regulator is boosted from zero until smoke is emitted in the tank. This is to immediately turn the output voltage of the voltage regulator to zero and cut off the power supply. The smoke is the grounding point. Pay attention to safety during the entire operation process. Place the motor on an insulating mat, and no one can touch the motor before the power is cut off. The treatment method is: carefully remove the slot wedge with the grounding slot, then put the motor into the oven to heat, bake the soft winding, and then carefully take out the wire turns in the slot and check the insulation of each wire. If the insulation is damaged, paint and dry, then re-place the insulating paper in the groove, and then put the removed wire turns into the groove, drive into the groove wedge, and immerse the winding with varnish and dry. If you find that the enameled wire has been burnt, pull the two broken ends to the ends of the windings, and then find an enameled wire with the same wire diameter and put it in the slot, and connect the wires at both ends of the winding. The joints should be twisted, soldered, painted, dried, and then covered with insulating sleeves. When tying the ends, pay attention to the tying joints. 3 Judgment of short circuit fault between stator winding turns The short circuit fault between the stator winding turns is generally judged by measuring the DC resistance of the three-phase winding. However, the DC resistance of the stator winding of a motor with a large capacity is very small, and the influence of the relationship between the accuracy of the instrument and the measurement error is not easy to draw a correct judgment, but the following methods can be used to judge. Without disassembling the motor, use a single-phase auto-voltage regulator with an appropriate capacity to gradually increase the voltage from scratch, and pass low-voltage alternating current to one of the phases. At the same time, use a clamp ammeter to measure the current so that the current rises to about 1/3 of the rated current of the motor. Then stop boosting and measure the induced voltages of the other two phases with a multimeter. If one phase has an inter-turn short-circuit fault, its induced voltage will be lower than the other phase. Then switch on one phase and use the same method to measure the induced voltage of the other two phases. According to whether the induced voltage is the same, it can be judged whether there is an inter-turn short-circuit fault. Short circuit failure between stator turns requires replacement of motor windings during maintenance. 4 Judgment of broken squirrel cage After the cage rotor is broken, it usually runs normally without load, but as soon as the load is added, the motor speed will decrease, the stator current will increase, the motor will vibrate, the temperature will increase, and there will be abnormal noise. The greater the load, the more broken bars, the more serious the above phenomenon. The method of judging whether the bar is broken is as follows: Energizing method: Use a single-phase voltage regulator with appropriate capacity to pass low-voltage alternating current to one-phase winding of the motor. The voltage regulator slowly boosts the voltage from zero, and at the same time measures the current with a clamp-on ammeter, and stops the boost when the current rises to about 1/2 of the rated current of the motor. Then slowly turn the shaft of the motor by hand and observe the pointer of the clamp-on ammeter. If the pointer does not move or swings slightly, it indicates that the rotor is in good condition. If the pointer swings periodically and the swing amplitude is large, it indicates that the rotor squirrel cage bar has a broken bar. Alternative method: Find a motor rotor with the same frame size and core size as this motor, and replace and install it on this faulty motor. Test run with the same load, all the above faults are eliminated. This proves that there is a problem with the rotor squirrel cage of this motor. 5 Repairs after the "Parallel Headgear Shooting" between the Motors After a short-circuit between the wire-wound motor and the headgear is broken down, a section of the wire will generally be burned off. The method of extension can be used when repairing. The specific methods are as follows: Use 1-2 250W infrared light bulbs to locally heat and soften the gun at the end of the rotor, remove the copper foam, and then slightly bend the burnt copper wire. Silver soldering or tin soldering can be used to connect long wires. Pay attention to protect the winding when welding, so as not to burn out the protection). Flatten the scar after welding. After trimming the copper wire straight, wrap it with a layer of glass ribbon, coat it with insulating paint, and dry it with an infrared bulb. When the wire is placed in its original position, put a layer of thin-film blue-shell paper under it, then cut off the excess part of the copper wire, put it in the headgear, and solder it. Then paint the repair place and dry it. The headgear should be made of copper sheet according to the original size, and the copper sheet should be tinned before making it. A motor with a parallel headgear has a relatively large capacity and is difficult to disassemble and assemble. The above method is suitable for on-site repair. 6 Removal of the old winding of the motor Generally, the soft winding must be baked first and then disconnected. But for larger capacity motors, it is difficult to bake and remove the wires, so the following methods can be used to remove the old windings. Use a flat spatula to remove one end of the winding, and the cut is flush with the notch. Cut the other end of the winding with iron scissors, then use a copper rod of appropriate thickness to punch out the enameled wire in the slot, and then clear the slot. If the copper rod is suitable and the operation method is correct, the wires in each slot can be punched out together. When using a flat shovel, be careful not to damage the stator core. When using the above method to remove the wire, the drying and softening process before the removal can be omitted, which saves time and energy, and the removal is relatively labor-saving. However, this method is suitable for motors with a capacity of 7.5KW or less. Because of the small housing of small motors or micro motors, it is inconvenient to use a flat shovel to operate. 7 Grinding of new brushes DC motors or rotors are renewal brushes of wound motors. When the brush holder is perpendicular to the surface of the commutator, the method of grinding the brush is: spread a piece of sandpaper on the surface of the commutator, hold a new brush of the same model and rub it back and forth along the axis of the commutator. The surface to be ground will soon be ground out of a curved surface that matches the surface of the commutator. Use coarser sandpaper first, then fine sandpaper. When grinding, hold the electric brush straight, move back and forth along the axis of the commutator, not be skewed, and the reciprocating stroke should not be too long. Pay attention to prevent the brush powder from entering the armature and commutator groove. After grinding, put the brushes into the brush holder. After the starter motor runs for a few minutes without load, take out the brushes for inspection. The contact surface should generally account for more than 80% of the total area. Otherwise, re-grind until it is qualified. When the brush holder of the motor is not perpendicular to the surface of the commutator, the following method should be adopted: spread sandpaper on a flat surface, and grind an inclined surface according to the inclination angle of the brush holder while holding the electric brush. Then put the brush into the brush holder, and turn the motor rotor by hand, so that the bright spots will be polished on the inclined surface of the brush, and then the bright spots will be polished with sandpaper. After polishing, put the brush into the brush holder and rotate the motor rotor by hand, and the bright spots will be polished again, the area is larger than the second. After doing this several times, the contact surface of the brush will become larger and larger and gradually form an arc. When sanding bright spots, don't sand too much each time, especially after the next time, be careful, just rub it lightly with fine sandpaper. If rubbed too much, the contact surface will become smaller instead. Practice has proved that using this method to grind inclined brushes has a fast time and good results. 8 Emergency repair of wear of rotor journal and end cover bearing chamber The specific methods and steps are as follows: First use ethanol or gasoline to repeatedly wash the areas to be repainted. Heat the ternary nylon ethanol solution into a transparent liquid. Use a small brush to moisten the liquid and apply a thin layer on the abraded area. For those with a larger amount of abrasion, extend the heating time to make the solution thicker and reapply. Generally, it needs to be applied several times until it reaches the required thickness. After the first application, it needs to be placed for about 3 minutes and allowed to dry by itself. The second application can be done when the hands are not sticky. To dry after application, heating can be used, or it can be allowed to dry naturally. If the abrasion is less than 0.10mm, it can be used after coating and drying. If the amount of wear is greater than 0.10mm, in order to ensure the concentricity of the stator and rotor when the motor is assembled, turning processing is required after coating. During turning, the bearing chamber of the repair end can be processed according to P6, and if the journal is repaired, it can be processed according to r6. After the coated nylon solution is completely dried, it will have sufficient adhesion and hardness, which can fully meet the requirements of the motor assembly. This method is only suitable for the situation where the amount of wear is not large, only a few tenths of a millimeter.