Why can't the frequency converter be equipped with leakage protector
Writer： Hengfeng you electric Time：2021-09-03 views：times
When using frequency converter, leakage protector must not be used. This is a major principle for the use of frequency converters.
Some customers choose the corresponding leakage protector for the frequency converter when using the frequency converter. The final result is that when the frequency converter moves together, the leakage protector acts, and the system cannot run at all.
Why?
The principle of leakage protector is that the zero sequence current is zero. When the frequency converter is used, the zero sequence current cannot be zero.
The output side of the frequency converter is PWM wave, and there is the capacitance effect of long cable between the motor cable and the earth. When the cable with shielding layer is used, the capacitance effect is more obvious. When the frequency converter works, the capacitor is charging and discharging, and current flows into the earth through the capacitor, and then flows back to the frequency converter from the grounding wire on the incoming side to form a current circuit. If a leakage protector is used on the incoming side, it will act and cut off the operation of the system.
So, don't equip your frequency converter with leakage protector. If you want to ensure safety, do a good job in equipment grounding.
Case:
Q: an 18.5kw frequency converter is installed for an 18.5kw boiler induced draft fan. As soon as the frequency converter is installed and started, the power distribution room will jump when it is opened,
Leakage protector (200mA action, 30mA pulse) is installed in each circuit of the original distribution room.
The customer was refused to remove the leakage protection. After that, the carrier frequency was adjusted to 1kHz and the starting mode of the frequency converter was changed, but it was still not solved,
Finally, it is suspected that the power line of the motor has leakage, because it is about 20m long and buried underground, but it is difficult for the customer to replace it (its original power frequency is normal).
Is there any simple and effective solution?
A: the leakage protector will trip when it detects that the three-phase imbalance is more than% 20. When the frequency converter is installed, the three-phase imbalance will generally exceed% 50,
So the leakage protector will jump.
Here are several methods:
Method 1: there is usually a regulator on the leakage protector, which can be turned up;
Method 2: replace the leakage protector with the special leakage protector for frequency converter. There are special leakage protectors for frequency converter on the market.
Method 3: increase the equipment load, that is, the motor load, and the leakage current of the frequency converter will not be very large when starting.
Method 4: short circuit the leakage protector.
