Impacts of distribution network unbalanced impedance on action performances of Residual Current Operated Device

Residual Current Operated Devices (RCDs) play an important part on the low-voltage electric safety, and offer a safe protection against electric shock hazards and fire hazards caused by earth faults on equipment. At present, all kinds of RCDs are usually prone to nuisance tripping and lower rate of operation due to non-fault conditions. This may arise due to a number of causes such as extraneous earth leakage paths, switching transients, harmonic currents and unbalanced impedance etc.. Through theoretical calculations, Matlab simulation and physical testing, this paper demonstrates the influence of unbalanced impedance on the action performance of RCD. The investigative results show RCD has lower the reliability as the symmetry of three-phase leakage impedance is lower. The conclusions could be of great value for the application of RCDs of different action time as well as the research and development of new type and high reliability RCDs.