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The use of frequency inverters in PLCS should be no stranger to everyone. However, when using frequency inverters, leakage protection devices must never be used. This is a major principle for the application of frequency inverters.
Some users have selected the corresponding leakage protection device for the frequency inverter when using it. The final result is that when the frequency inverter starts working, the leakage protection device activates, and the system simply cannot operate.

Then why is that?
The principle of a leakage protection device is that the zero-sequence current is zero. When using a frequency inverter, the zero-sequence current cannot be zero. The output side of the frequency inverter is a PWM wave. There is a capacitance effect of long cables between the motor cable and the ground. When using cables with shielding layers, the capacitance effect is more obvious. When the frequency inverter is in operation, the capacitor is charging and discharging. Current flows through the capacitor into the ground and then returns to the frequency inverter from the grounding wire on the incoming line side, forming a current loop. If a leakage protection device is used on the incoming line side, it will act and cut off the system operation. So, don't install a leakage protection device for your frequency inverter. If safety is to be ensured, it is sufficient to properly ground the equipment.

This case:
A 18.5KW boiler induced draft fan was equipped with a 18.5KW frequency inverter. Once the frequency inverter was installed and started, the circuit breaker of the distribution room tripped. It turned out that each circuit in the distribution room was installed with a leakage protection device (200mA action, 30mA pulse). The request for the customer to remove the leakage protection was refused. Later, the carrier frequency was adjusted to 1KHz and the start-up method of the frequency inverter was changed, but the problem still could not be solved. Finally, it was suspected that the power cord of the motor was leaking electricity because it was about 20 meters long and buried underground. However, it was also difficult to ask the customer to replace it (the original power frequency was used normally).

May I ask if there are any simple and effective solutions?

Solution: Since a leakage protection device usually trips when it detects a three-phase unbalance degree of above, after installing a frequency converter, the three-phase unbalance degree generally exceeds the operating value, so the leakage protection device will definitely trip. The following are several methods:

Method One: There is usually a regulator on a leakage protection device. Just increase the regulator.

Method Two: Replace the leakage protection device with a dedicated leakage protection device for frequency converters. There are dedicated leakage protection devices for frequency converters available on the market.

Method Three: Increase the load on the equipment, that is, the motor load. In this way, the leakage current of the frequency converter will not be very large when it starts.

Method Four: Short-circuit the leakage protection device.