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Inverter leakage troubleshooting

Feb 19, 2021

Inverter leakage troubleshooting

There are distributed capacitances in the inverter input/output wiring and the motor. When the leakage current flows, its value is determined by the distributed capacitance and carrier frequency. The countermeasures that can be adopted are shown in the table.

Countermeasures for Inverter Leakage

1. Leakage current to earth

Leakage current not only flows through the inverter's own system, but sometimes flows to other systems through grounding wires, etc., so the following measures are often taken to suppress:

1) Reduce the carrier frequency of the motor. Note that this will increase the motor noise. Choosing flexible PWM will make the increase of motor noise not a problem.

2) By using the leakage circuit breaker designed for high harmonics and surge leakage current in the inverter's own system and other systems, it can operate under low noise.

3) Note that the increase in wiring length will cause an increase in leakage current. Reduce the carrier frequency of the inverter to reduce the leakage current.

4) Increasing the motor capacity will increase the leakage current.

2. Leakage current between lines

Due to the high portion of the current flowing through the distributed capacitance between the inverter output wiring, the external thermal relay may sometimes cause unnecessary actions. With the small capacity of the 400V series, when the wiring is long, the ratio corresponding to the rated current of the motor will increase. Therefore, the thermal relay used externally is prone to unnecessary operation (the leakage current path between the lines is shown in Figure 9-2. Show), the following measures can be taken to restrain:

Leakage current path between lines

1) Use the electronic overcurrent protection of the inverter.

2) Reduce the carrier frequency. Please note that the motor noise will increase at this time. Selecting flexible PWM will make the increase of motor noise not have harmful effects.

In order to ensure that the motor is not affected by the leakage current between the wires, it is recommended to use a temperature sensor to directly detect the motor temperature.