Source：Shengda Yu Published：2020-08-20 Clicks：7936
Due to the insulation damage caused by excessive motor current, excessive power supply voltage variation, single-phase operation, mechanical bruising, poor manufacturing, etc., it is divided into winding turn-to-turn short circuit, winding-to-winding short-circuit, winding-to-pole short-circuit and winding-to-phase short circuit.
Fault phenomenon: the magnetic field distribution of ions is uneven, and the imbalance of three-phase current leads to the aggravation of vibration and noise when the motor is running. in serious cases, the motor can not start, but a large short-circuit current is produced in the short-circuit coil, which causes the coil to heat up quickly and burn out.
Causes: insulation aging and loss of insulation due to long-term overload of motor; insulation damage caused by wire embedding; insulation breakdown caused by the decrease of insulation resistance caused by moisture in windings; damage when end and interlayer insulation materials are not properly padded or shaped; insulation damage of end connection wire; insulation breakdown caused by overvoltage or lightning strike; insulation damage caused by friction between rotor and stator winding. The metal foreign body falls into the inside of the motor and there is too much oil.
Inspection method:
1) external observation: observe whether the junction box and the end of the winding are charred or not. when the winding is overheated, it leaves dark brown and has a bad smell.
2) temperature detection method: no-load operation for 20 minutes, should stop immediately when abnormal is found, and touch whether each part of the winding exceeds the normal temperature with the back of the hand.
3) electrification experiment method: measured by ammeter, if the current of a phase is too large, it shows that the phase has a short circuit.
4) Bridge inspection: when measuring the DC resistance of a winding, the difference should not be more than 5%. If the difference is more than 5%, the phase with low resistance will have a short circuit fault.
5) short-circuit detector method: if there is a short circuit in the tested winding, the steel sheet will vibrate.
6) Multimeter or mega-ohmmeter method: measure the insulation resistance between any two-phase windings. If the reading is very small or zero, it means that there is a short circuit between the two-phase windings.
7) Voltage drop method: the three windings are connected in series and connected to low-voltage safe AC, and it is found that the small group has short-circuit fault.
8) current method: motor no-load operation, first measure the three-phase current, in the exchange of two-phase measurement and comparison, if it does not change with the power exchange, the larger current one-phase winding has a short circuit.
Motor maintenance method:
1) short circuit at the end: separate the short circuit point with insulating material or repackage the insulated wire, and then paint and dry.
2) short circuit online slot: after softening, find out the short circuit point to repair, put it back into the wire slot, and then paint and dry.
3) for each phase winding in which the turn of the short line is less than 1 stroke 12, all the short lines are cut off when the number of turns in series is connected, and the conduction part is connected to form a closed loop for emergency use.
4) when the number of turns of the short circuit point of the winding exceeds 1 / 12:00, all the windings should be removed and rewound.