Inspection method of three-phase motor

(1) Observation method. By visually inspecting the winding end and the insulator in the trunking, observe whether there are traces of damage and charring, and if so, it is the grounding point.
(2) Multimeter inspection method. Check with a multimeter low resistance, the reading is small, it is grounded.
(3) Megohmmeter method. According to different levels of different megohmmeters 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 broken down due to accidents, it needs to be determined by 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 means that the winding is grounded, and if it is found that there is a spark or smoke somewhere, it is a winding ground fault point. If the lamp is slightly bright, the insulation has ground breakdown. If the lamp does not light up, but a spark also appears when the test rod is grounded, it means that the winding has not broken down, but it is seriously damp. You can also use hardwood to tap on the edge of the stop of the shell, knock to a certain place and wait for a light to turn off, indicating that the current is on and off, and this place is the grounding point.
(5) Electric penetration method. With a voltage regulating transformer, after connecting the power supply, the grounding point quickly heats up, and the place where the insulation smokes is the grounding point. Special attention should be paid to the small motor should not exceed twice the rated current, and the time should not exceed half a minute; The large motor is 20%-50% of the rated current or gradually increases the current, and the power is immediately cut off when there is smoke at the grounding point.
(6) Group elimination method. For the grounding point is in the core of the iron core and the burning is relatively strong, the burned copper wire is fused with the core. The method used is to divide the grounded one-phase winding into two halves, and so on, and finally find the grounding point.