Common method for finding grounding points - Solutions - Huaqiang

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1) Shake table method For 6kV motor, if the winding-to-ground insulation resistance is below 6MΩ, the winding is wet or the insulation is deteriorated; if it is zero, it is grounded.
(2) Check the lamp method to remove the end cover, take out the rotor, disassemble the phase windings, connect a 60W, 220V bulb in series between the end of the measured winding and the motor casing, and connect 220V AC at both ends of the tested winding. Voltage, if the bulb is red, it means poor insulation, often called "virtual connection": If the bulb is very bright, it means that there is winding grounding, often called "real connection". If it is "real connection", the insulation at the grounding place often has cracks and blackening marks. You can look for the grounding point at the notch by observing it; if it is "virtual connection", in order to find the grounding point, it can be connected to the virtual high voltage. The part is broken down, and the grounding point is judged by sparks or smoke marks.
(3) Current Orientation Method: Add DC voltage to the first end of the fault phase in parallel. Use 6-12V battery and connect the adjustable resistor in series. The current is controlled within 5A. Move the small magnetic needle slot by slot. The direction of the magnetic needle changing direction is the grounding point. groove. The magnetic needle is then moved axially along the slot, and the magnetic needle changes direction at the point of failure. If conditions permit, we can also use current burn-through or voltage drop to find the grounding point.
According to past experience, the general winding grounding point occurs at the slot or end, and rarely occurs in the slot, because the end is a weak point of insulation, because the two ends of the stator winding are affected as the motor capacity increases. The frequency-doubled electromagnetic force increases accordingly. If the natural frequency of the end of the stator winding is close to 100 Hz, a large resonant amplitude will be generated at the end of the winding during operation, and the overall modal frequency of the winding end is close to 100 Hz and the amplitude is elliptical. The most serious time. In recent years, large motors have been caused by the resonance of the stator winding ends or other reasons, such as loose ropes, bracket fixing bolts, loose fasteners in the slots, and wire rod insulation wear.