Zhejiang Shuyi Electric Co. Ltd

When using the inverter, the leakage protector must not be used. This is a major principle for the use of the inverter.

Some customers choose the corresponding leakage protector for the inverter when using the inverter. The final result: as soon as the inverter starts, the leakage protector starts, and the system cannot run at all.

The principle of the leakage protector is that the zero sequence current is zero. When using the inverter, the zero sequence current cannot be zero.

The output side of the inverter is a PWM wave, and there is a capacitive effect of a long cable between the motor cable and the ground. When a cable with a shielding layer is used, the capacitive effect is more obvious. When the inverter is working, the capacitor is charging and discharging, and the current flows into the ground through the capacitor, and then flows back to the inverter from the ground wire on the incoming side to form a current loop. If an earth leakage protector is used on the incoming side, it will act to cut off system operation.

So, don’t equip your inverter with a leakage protector. If you want to ensure safety, do a good job of grounding the equipment.

Case Studies:

Question: A 18.5kW inverter is installed on a 18.5kW boiler induced draft fan. After the inverter is installed, the power distribution room will trip when it is opened. 30mA pulse).

Asking the customer to remove the leakage protection was rejected, and then adjusted the carrier frequency to 1kHz, and changed the starting method of the inverter, but it still could not be solved. Finally, it was suspected that there was leakage in the power line of the motor, because it was about 20 meters long and buried in the ground, but the customer was required to It is also difficult to replace (its original power frequency is normal).

Simple and effective workaround:

Answer: Because the leakage protector generally detects that the three-phase unbalance is more than 20%, it will trip protection. When the inverter is installed, the three-phase unbalance will generally exceed 50%, so the leakage protector will definitely trip. Here are a few ways:

Method 1: There is generally a regulator on the leakage protector, and the regulator can be adjusted to a larger size; Method 2: Replace the leakage protector with a special leakage protector for frequency converters, ZJSHUYI sells special leakage protectors for frequency converters;

Method 3: Increase the equipment load, that is, the motor load, so that the leakage current of the inverter will not be very large when it starts;

Method 4: Short-circuit the leakage protector.


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