1. Reasons for Short Circuit Faults of Motor Windings
(1) The long-term overload of the motor causes aging of the insulation.
(2) Insulation damage caused by wire insertion.
(3) The damp winding reduces the insulation resistance and causes insulation breakdown.
(4) Insulation breakdown due to overvoltage or lightning strike.
(5) Insulation damage is caused by friction between rotor and stator winding ends.
(6) Insulation damage caused by rotor sweeping heat.
(7) Metal foreign materials fall into the motor and oil stain is excessive.
2. Inspection Methods
(1) External observation. Observe whether the junction box and winding end are burnt or not. After the winding is overheated, it leaves dark brown and has a peculiar smell.
(2) Temperature detection method. Running without load for 20 minutes (stop immediately when abnormal is found), touch each part of the winding with the back of your hand to check if it exceeds normal temperature.
(3) Electricity experiment method. Measured by ammeter, if the current of a phase is too large, it indicates that there is a short circuit in the phase.
(4) bridge inspection. When measuring the DC resistance of each winding, the difference should not exceed 5%. If the difference exceeds, there will be short circuit fault in the phase with small resistance.
(5) Multimeter or megohmmeter method. Measuring the insulation resistance between any two-phase windings, if the reading is minimal or zero, shows that there is a short circuit between the two-phase windings.
(6) voltage drop method. Three windings are connected in series and connected to low voltage safe alternating current. A group of short circuit faults with low voltage are detected.
(7) current method. In no-load operation of the motor, the three-phase current is measured first, and then the two-phase current is measured and compared. If it does not change with the change of the power supply, the one-phase winding of the larger current will be short-circuited.