When using an inverter, a leakage maintainer must not be used. This is a major principle of the use of frequency converters.
Some users choose the corresponding leakage maintainer for the inverter when using the inverter. * The result is that the inverter moves together, the leakage maintainer acts, and the system cannot operate at all. Why?
The principle of a leakage maintainer is that the zero sequence current is zero. When using an 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, which is more pronounced when using a shielded cable. During the operation of the inverter, the capacitor is charging and discharging, and the current flows into the ground through the capacitor, and flows back to the inverter from the grounding wire on the incoming side to form a current loop. If a leakage maintainer is used on the incoming side, it will operate and cut off the system. So, don't equip your drive with a leakage maintainer. If you want to ensure safety, just do a good job of grounding the equipment.
Example: Q: An 18.5KW boiler induced draft fan is installed with an 18.5KW inverter, as soon as the inverter is started, the power distribution room will jump when it is opened, and the original power distribution room is equipped with a leakage maintainer (200mA action, 30mA pulse). The customer was asked to remove the leakage maintenance was refused, and then the carrier frequency was adjusted to 1KHz, and the starting method of the inverter was still not dealt with, * After the doubt that the power line of the motor has leakage, because its length is about 20 meters and buried in the ground, but it is also difficult to require the customer to replace it (its original power frequency is used normally). Is there a brief and useful way to deal with it?
Answer: Because the leakage maintainer generally detects that the three-phase unbalance is more than %20, it will skip maintenance, and when the three-phase unbalance degree is installed after the inverter, the three-phase unbalance will generally exceed %50 or more, so the leakage maintainer will definitely jump.
Here are a few ways to do it:
Method 1: There will generally be an adjuster on the leakage maintainer, and the regulator can be adjusted to a larger size.
Method 2: Replace the leakage maintainer with a special leakage maintainer for the inverter, and there are special leakage maintainers for the inverter on the market.
Method 3: Increase the load of the equipment, that is, the load of the motor, and the leakage current of the inverter will not be very large when it is started.
Method 4: Short the leakage maintainer.
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