This is because the output waveform of the inverter contains higher harmonics, and the cable between the motor and the inverter and the motor generates leakage current. This leakage current is much larger than that of the power frequency drive motor, so this phenomenon occurs.
The leakage current on the output side of the inverter is about three times that of the power frequency operation. In addition to the leakage current of the motor, the operating current of the selected leakage protector should be greater than 10 times of the leakage current at the power frequency. The protection switch (circuit breaker) with leakage protection is not suitable for the place where the inverter is used. Because the output of the inverter has higher harmonics, if it is not a dedicated inverter cable and variable frequency motor, the leakage current is unavoidable, and often exceeds 30 mA, causing the leakage protection to trip.