The use of frequency converter, in the PLC, we should not feel strange, and in the use of frequency converter, must not use leakage protector. This is a major criterion for the application of frequency converters. 

Some users in the use of frequency converters, for the converter to choose the corresponding leakage protector. The final result is: frequency converter start, leakage protector on the action, the system simply can not run.

And why is that?

The principle of leakage protector is that zero sequence current is zero. 

The use of frequency converter, zero-sequence current can not be zero. The output side of the inverter is PWM wave, the capacitance effect of the long cable between the motor cable and the Earth is more obvious when the cable with shield layer is used. When the inverter works, the capacitor is charging and discharging, and the current flows into the earth through the capacitor, and then flows back to the inverter from the grounding wire on the incoming line side to form a current loop. If the leakage protector is used on the incoming side, it will act to cut off the system operation. 

So, do not for your inverter leakage protector. If you want to ensure safety, make the equipment grounded on the line.

Case in point:

A 18.5 kw boiler induced draft fan installation of a 18.5 kw inverter, after the installation of the inverter after the start of the distribution room on the trip, the original distribution room every road installed leakage protector (200mA action, 30mA pulse) . 

The request that the customer remove the leakage protection was refused, and then the carrier frequency was adjusted to 1 khz, and the change of the starting mode of the frequency converter could not be solved. 

Finally, it was suspected that the power cord of the motor had leakage because it was about 20 meters long and buried underground, but it is also difficult to ask customers to change (its original power frequency normal use) .

Is there any simple and effective solution?

Solution: as the leakage protector is generally detected three-phase imbalance for more than the jump protection, when the installation of the inverter three-phase imbalance will generally exceed the action value above, so the leakage protector will jump.

The following several methods: 

Method One: Leakage Protector on the general will have a regulator, the regulator can be adjusted; 

Method Two: Leakage Protector replaced by special leakage protector frequency converter, on the market have sell frequency converter special leakage protector. 

Method Three: increase the device load, that is, motor load, frequency converter in the start-up leakage current will not be very large. 

Method Four: the leakage protector short-circuit off.