Detecting High-Impedance Fault with Z-Source Circuit Breakers in Smart Grids

High-impedance faults (HIFs) are almost "invisible" to protective devices but may create destructive damage to electric devices. It is a challenging task to distinguish HIFs from normal operation and fault conditions. Most fault protective devices and relays response to a fault current that is higher than twice the steady-state current rating. Therefore, the HIFs should be detected for power system operators to take proper actions. In this paper, a new method of detecting HIFs is developed based on the status monitoring of Z-source circuit breakers (ZCBs) in the DC section of smart grids. It is noticed that the ZCB can response to a HIF when the capacitances are properly specified in the ZCB circuit. By adjusting the Z-source capacitance values properly, the ZCB can be freely controlled to operate in the HIF detection mode and the HIF interruption mode. At the same time, the original high-current fault interruption of ZCB remains unchanged. The relationship between the maximum HIF resistance and required Z-source capacitance has been derived and its effectiveness and accuracy have been verified by experiment tests.