leakage current is the current formed between mutually insulated windings or between windings and casing in a motor through the surface of surrounding medium or insulator when voltage is applied, which is generally expressed by effective value.
when the leakage current flowing through the motor insulation medium is not close to the breakdown voltage, its magnitude changes linearly with the applied voltage, and its law conforms to ohm's law. Only when the applied voltage is close to the breakdown voltage value, its current suddenly changes.
The insulation dielectric strength test may damage the insulation of the motor or reduce its safety factor. Therefore, it is not appropriate to repeatedly apply the test voltage to the same motor. DC voltage has the same ability as AC voltage in checking design and structural defects, but its damage is relatively small. However, it is generally stipulated to use AC voltage, because high-voltage AC is relatively easy to obtain.