Since the input and output currents of an inverter contain high-frequency components, the leakage current generated 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 the high-frequency signals can induce unwanted currents through parasitic capacitances in the wiring and equipment. Given the variety of circuit breakers available, there are situations where even if the insulation of the inverter cables and motor is intact, the high-frequency leakage can still cause false tripping. Therefore, the most probable causes are either a leakage current threshold that is too low or excessive harmonic distortion from the inverter.
To address this issue, several countermeasures can be implemented:
1. Increase the sensitivity setting of the residual current device (RCD) to a level that is acceptable and prevents unnecessary tripping while still ensuring safety. 2. Use an earth leakage circuit breaker that is specifically designed to handle high harmonic content, which can reduce false trips caused by inverter-generated noise. 3. Install a zero-phase reactor between the power supply and the inverter to suppress any zero-sequence currents that may contribute to leakage. 4. Reduce the length of the cable connecting the inverter to the motor and ensure that the wiring is not in contact with the ground. This helps minimize stray capacitance and, consequently, reduces leakage current. 5. If adjusting the RCD’s sensitivity is not feasible, consider adding an isolation transformer in the branch circuit that includes the inverter. This can help isolate the system and reduce the impact of high-frequency components. 6. Choose cables with lower capacitive characteristics to further minimize leakage current. Additionally, using shielded cables may also provide extra protection against electromagnetic interference and leakage issues.
By implementing these measures, it is possible to significantly reduce the risk of false tripping due to inverter-induced leakage currents, ensuring a more stable and reliable operation of the electrical system.
Steel cross arms of different configurations are used on overhead lines, transmission towers, transmission lines, wood poles, utility poles, power poles, and light poles.
To make the steel cross arm more stable, there will be two cross arm braces to support the main cross arm by delta connection.
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