Fault recorder is a device that can automatically record all analog and switching value data in case of power system fault and shock. It will not start or only scan data under correct conditions. It will record the wave in case of fault or shock, and record the changes of voltage, current and power and relay protection action in the whole process before and after the fault.

        In the event of an accident in the power system, although the relay protection device trips and removes the fault, sometimes several sets of protection devices may act at the same time, some of which act correctly, while others may act wrongly.

        If there is no fault recording graphic analysis and the fault is represented only by the signal relay on the protection screen, when the signal relay on the protection screen is abnormal, such as the signal relay is stuck or refuses to operate, and even some places forget to turn on the signal power source after the inspection of the protection device, so that the line has a transient fault, Although the protection device acted correctly, tripped and reclosed successfully, the signal relay on the protection screen showed no indication, as if the protection device had never acted. Therefore, the work of relay protection and automatic device can not be evaluated correctly only by the signal representation of protection device. With fault recording, the correctness of relay protection device can be correctly evaluated or checked by analyzing the recording data. Especially in case of switching fault, fault recording data are needed to correctly evaluate the work of relay protection and reclosing device.