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Dry goods! Several practical methods in motor repair

Hits:Updated:2020-04-14 09:04:16【Print】

First, the treatment of reducing the motor insulation resistance after installing the end cover
Before the cage motor is repaired, the windings are well insulated to the casing before the two end covers are installed. When installed, the insulation resistance decreases. This phenomenon can be judged that the failure occurred at both ends of the winding. The cause of the decrease in insulation resistance may be that the paint film on the enameled wire is partially broken or the winding end of the winding die is protruded longer. After the end cap is covered, the inner wall of the end cap approaches or contacts the fault point, so the insulation resistance of the winding is reduced.
To eliminate such a fault, first determine which side of the motor the fault is on.
The judgment method is: first install an end cover, and use a 500V insulation resistance meter to measure the insulation resistance of the winding. If it is very low, it means that there is a fault at this end of the winding. Then, remove this end cap, then install the other end cap, and measure the insulation resistance of the winding. If it is also low, it means that there is a fault at the other end. In the process of removing and installing the end cover, the rotor may not be installed.
After identifying the faulty end, generally shape the winding end slightly and apply some insulating paint. If the problem is not solved, you can pad a layer of thin-film green shell paper on the outer side of the winding end and the inner side of the end cover. Generally eliminated.
Second, find and deal with the ground point in the stator winding slot
The stator winding is grounded in the slot, and it usually occurs at the slot. The slot insulation paper is skewed or damaged at the slot, or the slot is underlined or crossed accidentally. Put the enameled wire under the slot insulation paper, or squeeze the slot insulation paper into the slot wedge. Cause ground fault.
For this kind of fault, we must first determine whether the motor winding is wet. If it is wet, we bake the motor and if the result is invalid, it is judged that there is a ground fault.
There are several ways to find a ground point:
1. Carefully check the lead wires and the two ends of the slot. It is found that the lead wires are intact, the slot insulation 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 pollution everywhere.
2. Untie the Y-type connection point of the stator winding, and measure the insulation resistance of each phase to find out the phase with ground fault.
3. Use a single-phase voltage regulator. The phase wire at the output end is connected to the lead-out wire of the phase with a ground fault. The neutral wire is connected to the motor casing. Then the voltage regulator is boosted from zero to the tank. Smoke, this is immediately the output voltage of the voltage regulator will be zero and cut off the power, the smoke point is the ground point. Pay attention to safety during the entire operation process. Put the motor on an insulating pad, and the person cannot touch the motor before turning off the power.
The processing method is: carefully remove the groove wedge with the grounding groove, then put the motor in the oven to heat it, soften the windings, and then carefully take out the turns in the groove and check the insulation of each wire. The damaged insulation should be painted and dried, and then the slot insulation paper is placed in the slot again, and the taken-out turns are put into the slot, driven into the slot wedge, and the winding is dipped and dried.
If it is found that the enameled wire has been burned out, pull the two wire break ends to the ends of the windings separately, then find an enameled wire with the same wire diameter into the slot, and connect the wires at both ends of the winding. The joint should be twisted, soldered, painted, dried, and then covered with an insulating sleeve. When bundling the ends, pay attention to the bundling joints.
Third, the judgment of stator winding interturn short circuit fault
Short-circuit faults in the stator windings are generally determined by measuring the DC resistance of the three-phase windings. However, the DC resistance of the stator winding of a large-capacity motor is small, and the influence of the relationship between the accuracy of the instrument and the measurement error makes it difficult to obtain a correct judgment. However, the following methods can be used to judge.
Without disassembling the motor, a single-phase auto-coupled voltage regulator with an appropriate capacity is used to gradually increase the voltage from zero, and low-voltage alternating current is supplied 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 use a multimeter to measure the induced voltages of the other two phases. If one phase has an interturn short circuit fault, its induced voltage is 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 voltages are the same, it can be determined whether there is an interturn short circuit fault. The stator turns are short-circuited and the motor windings need to be replaced during maintenance.
4. Judgment of broken squirrel cage bars
After the cage rotor is broken, it usually runs normally at no load, but once the load is added, the motor speed decreases, the stator current increases, the motor vibrates, the temperature increases, and it will be accompanied by abnormal noise. The larger the load, the more broken bars, the more serious the above phenomenon.
The method of judging whether the bar is broken is as follows:
1. Power-on method: Use a single-phase voltage regulator with appropriate capacity to apply low-voltage AC power to the one-phase winding of the motor. The voltage regulator gradually increases the voltage from zero, and at the same time measures the current with a clamp ammeter to increase the current to about 1/2 of the rated current of the motor, and stops the voltage increase. Then slowly turn the shaft of the motor by hand and observe the pointer of the clamp ammeter. If the pointer does not move or slightly swings, it indicates that the rotor is intact. If the pointer swings periodically and the swing amplitude is large, it indicates that the rotor squirrel cage has broken bars.
2. Replacement method: It is to find a motor rotor with the same frame number and iron core number as this motor, and replace and install it on this faulty motor. With the same load test run, all the above faults are eliminated. This proves that the rotor squirrel cage of this motor is indeed a problem.
Fifth, the repair between the motor and the "cantilevered gun"
After a short-circuit between the wire-wound motor and the headgear, the wire head is generally burned for a short period of time. The lengthening method can be used for repair. The specific method is as follows:
Use 1-2 250W infrared light bulbs to partially heat and soften the rotor end and the gun, remove the copper foam, and then bend the burned (flat) copper wire slightly (to facilitate welding). The extended wire can be silver or soldered. When welding, pay attention to protect the windings to prevent burnout (protected with wet asbestos cloth (rope)). Flatten the welding scar after welding. After the copper wire is trimmed and straightened, a glass ribbon is wrapped around, coated with insulating paint, and dried with an infrared light bulb. When the wire is placed in its original position, a layer of thin-film green shell paper is placed under it, and then the excess part of the copper wire is cut off, put into a hood, and soldered. Finally, paint at the repair place and dry. The hood is made of copper sheet in the original size. The copper sheet should be tinned before production.
Motors with parallel hoods have large capacity and are difficult to disassemble and assemble. The above method is suitable for field repair.
Removal of old windings of electric motors
Generally, the soft winding should be dried before the wire is disconnected. However, the larger-capacity motors are more difficult to soften and disconnect, so the following methods can be used to remove the old windings:
With a flat spatula, remove one end of the winding, and the cut is flush with the slot. The other end of the winding is cut with iron scissors, and then the enameled wire in the slot is punched out with a suitable thickness of copper rod, and the slot is finally cleared. If the copper rod is suitable and the operation method is correct, the wires in each slot can be punched together. When using a flat shovel, be careful not to shovel the stator core.
When the wire is disassembled by the above method, the softening process before disassembly can be omitted, saving time and energy, and the disassembly is relatively labor-saving. However, this method is suitable for motors with a capacity of less than 7.5KW. Because the casing of small motors or micromotors is small, it is inconvenient to use a flat shovel.
Grinding of new brushes
The DC motor or rotor is a wire-wound motor to update the brush. 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 and hold a new model of the same type The brush rubs back and forth along the axial direction of the commutator, and the ground surface of the brush will be quickly ground out to match the surface of the commutator. Use coarser sandpaper first, then fine sandpaper. When grinding, the brush should be held in the right direction, and the back and forth movement must be in the direction of the axis of the commutator. It cannot be deflected, and the reciprocating stroke should not be too long. Care must be taken to prevent brush powder from entering the armature and commutator grooves. After grinding, put the brush into the brush holder. After starting the motor for a few minutes with no load, check out each brush. The contact surface generally accounts for more than 80% of the total area. Otherwise, it must be reground 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 used: spread the sandpaper on a flat surface, and use a brush to grind an inclined surface according to the inclination angle of the brush holder. Then install the brush into the brush holder, and turn the motor rotor by hand, so that the bright points will be polished on the inclined surface of the brush, and then polished with sandpaper (can also be scraped with a knife). After grinding, install the brush into the brush holder, and rotate the motor rotor by hand, and the bright spots will be sharpened again. The area is larger than the first time. Do this several times, the contact surface of the brush will become larger and larger, and gradually form an arc. When polishing bright spots, do not polish too much each time, especially the last time, you must be careful, just rub a little with fine sandpaper. If rubbed too much, the contact surface will become smaller instead. It has been proven in practice that grinding inclined brushes with this method is fast and effective.
Eight, emergency repair of rotor journal and end cap bearing chamber wear
The specific methods and steps are as follows:
1. First, wash the place with ethanol or gasoline repeatedly.
2. Heat the ternary nylon ethanol solution into a transparent liquid. Use a small brush to dip the liquid and apply it to the abraded area. For slightly larger abrasion, you can extend the heating time to make the solution thicker and then apply. Generally, it needs to be applied several times until it reaches the required thickness. After the first application, it needs to be left for about 3 minutes and dried by itself. It can be applied a second time when it is not sticky.
3. After drying, it can be dried by heating (the temperature does not exceed 80 ℃, the time is 0.5-1 hour), or it can be allowed to dry naturally (at room temperature 20 ℃, it should be placed in a ventilated place for about 36 hours).
4. If the amount of wear is less than 0.1mm, it can be used after being dried. If the amount of wear is greater than 0.10mm, in order to ensure the concentricity of the stator and the rotor when the motor is assembled, it needs to be turned after coating. When turning (if the dimensions of the outer and inner rings of the original bearing are within their tolerances), the repair of the bearing housing of the end cover can be processed according to P6. If the journal is repaired, it can be processed according to r6.
After the coated nylon solution is completely dried, it has sufficient differential force and hardness, which can fully guarantee the requirements of the motor assembly.




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