Since the input and output currents of an inverter contain high-frequency components, the leakage current caused by these components when driving with an inverter is typically higher compared to when the system is powered directly from the grid. This is because high-frequency signals can more easily pass through parasitic capacitances in the wiring and equipment. With various types of circuit breakers available, there are situations where even if the insulation of the inverter cables and motor is intact, the presence of high-frequency harmonics may still cause the circuit breaker to trip erroneously. Therefore, the most common causes of such issues are either a leakage current threshold that is set too low or excessive harmonic distortion from the inverter.
To address this problem, several effective measures can be taken:
1. Increase the sensitivity level of the residual current device (RCD) to a value that is acceptable and less likely to trigger due to normal high-frequency noise. This helps prevent unnecessary tripping without compromising safety.
2. Use an earth leakage circuit breaker that is specifically designed to handle harmonic currents. These devices are more resistant to false trips caused by non-sinusoidal waveforms.
3. Install a zero-phase reactor (also known as a common-mode choke) between the power supply and the inverter. This component helps suppress common-mode currents, which are often responsible for increased leakage.
4. Try to minimize the length of the cable connecting the inverter to the motor. Also, avoid laying the cables directly on the ground, as this can increase stray capacitance and thus the potential for leakage current.
5. If it's not possible to adjust the RCD’s sensitivity, consider adding an isolation transformer in the branch circuit that includes the inverter. This can help reduce the coupling of high-frequency components to the protective earth system.
6. Choose cables with lower capacitive characteristics. Cables with reduced electrostatic capacity can significantly decrease the amount of leakage current generated by high-frequency switching.
By implementing these solutions, you can effectively manage the challenges posed by inverter-induced leakage currents and ensure the reliable operation of your electrical system.
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