When a short circuit occurs between turns of the motor, the following phenomena will occur:

1) A large circulating current will flow through the short-circuited coil (often up to 2-10% of the normal current) times), causing serious heating of the coil;

2) The three-phase current is unbalanced and the motor torque is reduced;

3) Noise is generated;

4) Short circuit In severe cases, the motor cannot be started with load.

At the beginning of an inter-turn short circuit, only two wires may be in contact due to worn insulation at the overlap.

Due to the circulating current generated in the short-circuit turns, the coil heats up rapidly, further damaging the insulation of adjacent wires, causing the number of short-circuited turns to increase and the fault to expand.

When there are enough short-circuited turns, the fuse will blow out or even the winding will burn and smoke. ?

When one phase of the three-phase winding has an inter-turn short circuit, it means that the number of turns of the phase winding is reduced, and the three-phase current of the stator is unbalanced. Unbalanced three-phase current causes the motor to vibrate and make abnormal sounds.

The average torque of the motor drops significantly, and it becomes weak when dragging the load.

Motor windings can be divided into centralized and distributed types according to the shape of the coil winding and the embedded wiring method. The winding and embedded assembly of concentrated windings are relatively simple, but their efficiency is low and their operating performance is poor.

Most AC motor stators use distributed windings. According to different models, models and coil embedding process conditions, the motors are designed with different winding types and specifications, so their winding technology The parameters are also different.

Winding short circuit

Short circuit between turns of the winding due to insulation damage caused by excessive motor current, excessive power supply voltage changes, single-phase operation, mechanical bumps, poor manufacturing, etc. , short circuit between windings, short circuit between winding poles and short circuit between winding phases.

1. Fault phenomenon

The magnetic field of ions is unevenly distributed and the three-phase current is unbalanced, which intensifies the vibration and noise of the motor during operation. In severe cases, the motor cannot start, and when the short circuit coil A large short-circuit current is generated in the coil, causing the coil to heat up quickly and burn out.

2. Causes

The motor is overloaded for a long time, causing the insulation to age and lose its insulation effect; insulation damage is caused when wires are embedded; the winding is damp, which reduces the insulation resistance and causes insulation breakdown; the end and The interlayer insulation material is not padded properly or is damaged during shaping; the end connecting wire insulation is damaged; overvoltage or lightning strikes cause insulation breakdown; the ends of the rotor and stator windings rub against each other causing insulation damage; metal foreign matter falls into the motor and oil pollution occurs many.

3. Inspection method

(1) External observation method. Observe whether the junction box and winding ends are burnt. The winding will leave a dark brown color and smell after being overheated.

(2) Temperature detection method. Run without load for 20 minutes (stop immediately if abnormality is found), and touch each part of the winding with the back of your hand to see if the temperature exceeds the normal temperature.

(3) Electrical test method. Use an ammeter to measure. If the current of a certain phase is too large, it means there is a short circuit in that phase.

(4) Bridge inspection. Measure the DC resistance of each winding. Generally, the difference should not exceed 5%. If it exceeds, the phase with the smaller resistance will have a short circuit fault.

(5) Short-circuit detector method. If the winding under test has a short circuit, the steel sheet will vibrate.

(6) Multimeter or megger method. Measure the insulation resistance between any two-phase windings. If the reading is extremely small or zero, it means there is a short circuit between the two-phase windings.

(7) Voltage drop method. After connecting the three windings in series, low-voltage safe alternating current was supplied, and a short-circuit fault was detected in the small group.

(8) Current method. When the motor is running with no load, first measure the three-phase current, then switch the two phases and measure and compare. If it does not change with the power supply switch, the one-phase winding with the larger current has a short circuit.

4. Short circuit treatment method

(1) The short circuit point is at the end. You can use insulating material to isolate the short-circuit point, or you can re-wrap the insulated wire, paint it and dry it again.

(2) The short circuit is in the wire slot. After softening it, find the short circuit point and repair it, put it back into the trunking, and then paint and dry it.

(3) For each phase winding with less than 1/12 short-circuit turns, cut off all short-circuit lines when the number of turns is connected in series, and connect the conductive parts to form a closed loop for emergency use.

(4) When the number of turns at the short-circuit point of the winding exceeds 1/12, all must be removed and rewound.