Fault handling of three-phase asynchronous motor

Winding is a component of the motor. Aging, moisture, heat, erosion, foreign matter intrusion, and external force can cause damage to the winding. Motor overload, undervoltage, overvoltage, and phase loss can also cause winding faults. Winding faults are generally divided into winding grounding, short circuit, open circuit, and wiring errors. Now explain the fault phenomenon, the cause and the inspection method.

Winding ground

Refers to the grounding caused by the winding and the core or the insulation of the casing.

1, the phenomenon of failure

The casing is charged, the control line is out of control, and the winding is short-circuited, causing the motor to fail to operate normally.

2, the cause

The winding is dampened to reduce the insulation resistance; the motor is overloaded for a long time; the harmful gas is corroded; the metal foreign matter invades the winding and damages the insulation; the insulation damages the iron core when rewinding the stator winding; the winding end touches the cover base; the stator and rotor friction cause insulation burn The insulation of the lead wire is damaged by the casing; the overvoltage (such as lightning strike) causes the insulation to break down.

3. Inspection method

(1) Observation method. Visually inspect the ends of the windings and the insulation in the wire trough to see if there are any signs of damage and burnt black, if any, the grounding point.

(2) Multimeter inspection method. Check with a multimeter low-resistance file. If the reading is small, it is grounded.

(3) Megohm method. According to different grades, different megohmmeters are used to measure the insulation resistance of each group of resistors. If the reading is zero, it means that the winding is grounded, but the motor insulation is damp or breakdown due to accidents, it is judged according to experience, generally speaking The pointer swings at "0" and is considered to have a certain resistance value.

(4) Test light method. If the test light is on, the winding is grounded. If a spark or smoke is found somewhere, it is the grounding fault point of the winding. If the lamp is slightly bright, the insulation has a ground penetrating. If the light does not illuminate, but the test rod is grounded, sparks also appear, indicating that the winding has not broken down, only severely damp. Hardwood can also be tapped on the edge of the outer edge of the outer casing. When it is knocked to a certain place, it will be turned off, indicating that the current is on and off, then it is the grounding point.

(5) Current through burning method. With a voltage regulating transformer, after the power is connected, the grounding point will heat up quickly, and the place where the insulator smokes is the grounding point. Special attention should be paid to the fact that the small motor must not exceed twice the rated current for less than half a minute; the large motor is 20%-50% of the rated current or gradually increase the current, and immediately turn off the power when the grounding point has just smoked.

(6) Group elimination method. The grounding point is inside the core and the burning is more severe. The burnt copper wire is fused with the iron core. The method used is to divide the grounded one-phase winding into two halves, and so on, and finally find the grounding point.

In addition, there are high-voltage test methods, magnetic needle exploration methods, power frequency vibration methods, etc., which are not introduced here.