Analysis and Handling Methods of Motor Winding Faults

Analysis and Handling Methods of Motor Winding Faults

The winding is a component of the electric motor, and aging, moisture, heat, corrosion, foreign object invasion, and external impact can all cause damage to the winding. Overloading, undervoltage, overvoltage, and phase loss operation of the motor can also cause winding faults. Winding faults are generally divided into winding grounding, short circuit, open circuit, and wiring errors. Now explain the fault symptoms, causes, and inspection methods separately.

Winding grounding refers to the grounding caused by insulation damage between the winding and the iron core or the casing.

Fault phenomenon

The casing is charged, the control circuit is out of control, and the winding is short circuited and heats up, causing the motor to malfunction.

cause

Moisture in the winding causes a decrease in insulation resistance; Long term overload operation of the electric motor; Corrosion caused by harmful gases; Metal foreign objects invade the interior of the winding and damage the insulation; Insulation damage and collision with iron core during rewinding of stator winding; The end of the winding touches the end cover of the machine base; Friction between the stator and rotor causes insulation burns; The insulation of the lead wire is damaged and collides with the shell; Overvoltage (such as lightning strikes) causes insulation breakdown.

Inspection Method

(1) Observation method. By visually inspecting the insulation at the end of the winding and inside the wire slot, observe for any damage or burnt marks. If there are any, it is the grounding point.

(2) Multi meter inspection method. Check with a multimeter in low resistance mode, if the reading is very small, it indicates grounding.

(3) Megohmmeter method. Select different megohmmeters according to different levels to measure the insulation resistance of each group of resistors. If the reading is zero, it indicates that the winding is grounded. However, for motor insulation that is affected by moisture or breakdown due to accidents, it needs to be judged based on experience. Generally speaking, when the pointer swings at "0", it can be considered to have a certain resistance value.

(4) Test lamp method. If the test light is on, it indicates that the winding is grounded. If sparks or smoke are found in a certain area, it is the fault point of the winding grounding. If the light is slightly on, there is a ground breakdown in the insulation. If the light is not on but sparks appear when the test rod is grounded, it indicates that the winding has not yet broken down, but is severely damp. You can also lightly tap the edge of the outer shell with hardwood, and when it turns off and on at a certain point, it indicates that the current is on and off, and that point is the grounding point.

(5) Electric current burning method. After connecting a voltage regulating transformer to the power supply, the grounding point quickly heats up, and the area where the insulation material emits smoke is the grounding point. Special attention should be paid to the fact that small motors should not exceed twice the rated current and the duration should not exceed half a minute; The large motor should have a rated current of 20% -50% or gradually increase the current, and immediately cut off the power when the grounding point starts to smoke.

(6) Group elimination method. For grounding points that are located inside the core of the iron and are severely burned, the burnt copper wire melts together with the iron core. The method used is to divide the grounded phase winding into two halves, and so on, and finally find the grounding point.

In addition, there are high-voltage testing method, magnetic needle exploration method, power frequency vibration method, etc., which will not be introduced one by one here.

processing method

(1) If the winding is damp and causes grounding, it should be dried first. When cooled to around 60-70 ℃, it should be coated with insulation paint and then dried.

(2) When the insulation at the end of the winding is damaged, insulation treatment should be carried out again at the grounding point, painted, and then dried.

(3) When the grounding point of the winding is in the slot, the winding should be rewound or some winding components should be replaced.

Finally, different megohmmeters should be used for measurement to meet the technical requirements.