This is because when we use the frequency converter, its output waveform contains high-order harmonics, and the motor and the cable between the frequency converter and the motor will produce leakage current, which will be much larger than the current when the motor is driven by power frequency, so the tripping phenomenon occurs. Isolation circuit breakers are generally used for the control of high-voltage electrical appliances. The molded case circuit breaker can automatically cut off the current when the current exceeds the trip setting.
In this case, we should also use leakage protector. When the leakage current at the frequency converter operation output side of the leakage circuit breaker is more than 3 times that of the power frequency operation, plus the leakage current at the motor, the action current of the leakage protector we selected should be greater than 10 times that of the power frequency operation.