Several methods in motor repair
3 Judgment of the inter-turn short circuit fault of stator winding
The short circuit fault of the stator winding is generally determined by measuring the DC resistance of the three-phase winding. However, the DC resistance of the stator winding of the motor with a large capacity is small, and the influence of the relationship between the accuracy of the meter and the measurement error is difficult to obtain a correct judgment, but the following method can be used to judge.
Without disassembling the motor, use a single-phase auto-coupled voltage regulator of appropriate capacity to gradually step up from zero and pass low-voltage alternating current to one of the phases. At the same time, the current is measured with a clamp-type ammeter to increase the current to about 1/3 of the rated current of the motor. Then stop the boost, use the multimeter to measure the other two-phase induced voltage separately. If one phase has a turn-to-turn short circuit fault, its induced voltage is lower than the other phase. Then, one phase is energized, and the induced voltages of the other two phases are measured in the same manner. According to whether the induced voltage is the same, it can be judged whether there is a turn-to-turn short circuit fault. Stator inter-turn short circuit fault, generally need to replace the motor winding during maintenance.
4 judgment of squirrel cage broken strip
After the cage rotor is broken, it is generally normal for no-load operation, but with the load, the motor speed is reduced, the stator current is increased, the motor is vibrated, the temperature is increased, and abnormal noise is accompanied. The greater the load, the more broken bars, the more serious the above phenomenon.
The method for judging whether a broken bar is as follows:
1. Power-on method: Use a single-phase voltage regulator with appropriate capacity to connect low-voltage AC to the motor's one-phase winding. The regulator gradually boosts from zero, and the current is measured with a clamp-type ammeter to stop 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 ammeter. If the pointer does not move or oscillate slightly, it indicates that the rotor is intact. If the pointer is periodically oscillated and the swing amplitude is large, it indicates that the rotor squirrel cage has a broken strip.
2, the alternative method: is to find a motor rotor with the same chassis number, the same as the iron core, replaced by the faulty motor installed. With the same load test, all the above faults are eliminated. This proves that there is a problem with the rotor cage of this motor.
