The conventional earth fault detection methods that measure residual currents cannot be applied to low voltage multi-earthed neutral systems (officially termed TN-C-S systems in both IEC and Chinese standards)

as they cannot distinguish between residual currents generated by load switching and those resulting from earth faults. To address this issue

equivalent circuits for three states of normal operation

load switching

and earth faults were established. The changing characteristics of residual currents were analyzed

and the equations describing the time-domain relationship between residual currents and mode-0 currents were constructed. The parameters of the equations were identified by the least-squares method to form the parameter vectors. The parameter vectors during load switching are close to those during normal operation

whereas the parameter vectors during earth faults are significantly different from those during normal operation. Earth faults can be identified by determining whether the magnitude difference between the parameter vector during residual current changes and that during normal operation exceeds a threshold value. The simulation and test results demonstrate that the proposed method is unaffected by factors such as earth fault arcs and distributed resources

effectively solving the problem of earth fault detection in TN-C-S systems.