Reduction of rating required for circuit breakers by employing series-connected fault current limiters

Calculation was made to examine the reduction of the rating required for circuit breakers by using series-connected resistive and inductive fault current limiters (FCLs) under various fault locations. In the model of the inductive FCL, a capacitance C-p consisting of a coil stray capacitance and a necessary additional capacitance was taken into account. The insertion of the resistive FCL and the inductive FCL with C-p = 100 nF into the power system proved to decrease the severity of the interrupting duty so that a lower-rated circuit breaker can be used. However, the introduction of the inductive FCL with C-p = 10 nF was found to lessen the fault current, while raising the rate of rise of the recovery voltage. From the variation of the breaking condition, the limiting impedance required to allow a circuit breaker to perform a satisfactory interruption is discussed.