Tripping Characteristics of Residual Current Devices Under Different Working Conditions

Residual current devices (RCDs) can be used to protect people and electric equipment against electric leakage and shocks in low-voltage power systems. However, action failures and nuisance tripping of RCDs can cause a lot of casualties and financial losses. Thus, in order to improve the safety and reliability of low-voltage power systems, it is necessary to study the tripping characteristics of RCDs to find out the reason of nuisance tripping and action failures of RCDs. In this paper, experiments were carried out to investigate the tripping characteristics of RCDs under different working conditions. The experimental results show that, for a sinusoidal residual current, the minimum tripping current rises with the increase of current frequency. When a sinusoidal current with low-order harmonic is applied, RCD tripping is decided by the residual current amplitude. What's more, for a surge current, the minimum tripping current decreases sensitively with the increase of current duration while the front time of the surge current has little influence on the minimum tripping current. Based on these test results, the reasons of action failures and nuisance tripping under actual working conditions have been analyzed and discussed, which can give help to the optimization and improvement of the existing RCDs.