FAST FAULT DETECTOR

A system and method for estimating fault current using a sliding observation window that is shorter than one cycle. The method may also include providing a pickup level that defines a current threshold for opening a switch in response to detecting the fault current; estimating the fault current from current measurement signals; accumulating time from a reset zero position during the time that the estimation of the fault current is greater than the pickup level; subtracting time from the accumulated time during the time that the estimation of the fault current is less than the pickup level after time has been accumulated from when the estimation of the fault current is greater than the pickup level; detecting the fault current if the accumulated time reaches a predetermined accumulation time; and opening the switch if the fault current is detected.