Causes of short circuit faults in the motor winding
(1) The motor is overloaded for a long time, which causes the insulation to age.
(2) Insulation damage caused by weaving.
(3) The winding is dampened, causing insulation breakdown to cause insulation breakdown.
(4) Overvoltage or lightning strikes to break down the insulation.
(5) The friction between the rotor and the stator winding ends causes insulation damage.
(6) Insulation damage caused by rotor broom heating.
(7) Metal foreign matter falls into the motor and there is too much oil.
(1) External observation method. Observe the junction box, the end of the winding is burnt, the winding is overheated and leaves a dark brown color, and has an odor.
(2) Temperature inspection method. Run for 20 minutes at no load (should stop immediately when an abnormality is found), and touch the parts of the windings to exceed the normal temperature.
(3) Power-on experiment method. When measuring with an ammeter, if a phase current is too large, it indicates that there is a short circuit in the phase.
(4) Bridge inspection. Measure the DC resistance of each winding. Generally, the phase difference should not exceed 5%. If it exceeds, the phase with a small resistance has a short circuit fault.
(5) Multimeter or megohm method. Measure the insulation resistance between any two phase windings. If the reading is very small or zero, it indicates that there is a short circuit between the two phases.
(6) Voltage drop method. After the three windings are connected in series and then connected to the low-voltage safety AC, a group with a small voltage is found to have a short-circuit fault.
(7) Current method. When the motor runs at no load, the three-phase current is measured first, and the two-phase measurement is exchanged and compared. If it is not changed with the power supply, the one-phase winding of the larger current has a short circuit.