Tripping Characteristics of Residual Current Devices Under Nonsinusoidal Currents

This paper presents an experimental investigation into the operating characteristics of residual current devices (RCDs) under an unbalanced current. The unbalanced current included the harmonic current, ground fault current, and surge current. A testing system was first set up in the laboratory, and the minimum values of the current causing RCD samples to trip were recorded. To obtain consistent testing results, RCD samples under test were demagnetized prior to each test. It is found that RCD tripping is primarily determined by the peak value of the unbalanced current. Under a ground fault, RCDs installed in healthy circuits may trip. It would be necessary to limit the maximum leakage current in the circuits to avoid such nuisance tripping. Under surge conditions, RCDs could withstand a large short-duration current. However, a long-duration surge current can easily cause RCDs to trip.