An analysis of solid-state fault current limiters for electric power distribution systems

Fault current limiters (FCL) are proposed to decrease fault current levels in distribution systems and thus minimizing damage to distribution equipment as a result of the initial large fault current peaks. This is possible because of the FCL capability of operating within a quarter cycle (compared with 3 or more cycles for typical circuit breakers). Among the different FCL technologies, this paper only considers solid-state FCL based on thyristors, which are preferred over those semiconductor devices that can be turned off by gate control (e.g., GTO, IGCT) because of their lower on-state voltage drops and higher current capabilities. Fault currents can be limited by either increasing the impedance along the path of the fault current (that is, inserting a resistor, an inductor or a resonant tank), or reducing the voltage applied to the fault (that is, operating the main thyristors as an ac-voltage controller). These four FCL types are evaluated and compared using circuit analysis and PSCAD (TM) simulations. A parametric analysis is performed to determine the impact of the fault-detection time delay, thyristor turn-off time, current-limiting impedance (R and L types), and resonant frequency (LC type) upon the FCL design. Finally, a simple case study of a 13.8-kV distribution system is presented taking into account all four FCL types.