Abstract: An apparatus which detects self-clearing faults in an AC power circuit carrying an electrical current is provided. To this end, the apparatus includes a fast element which detects an occurrence of a fault within one cycle of initiation, detects a clearing of the fault within one cycle of the clearing, and detects a duration of the fault to within one cycle or less. The apparatus further includes a self-clear element which compares the duration of the fault to a predetermined portion of a cycle of the electrical current to determine if the fault is self-clearing.

Abstract: A data switch for transferring data from either actual line readings or from stored memory to the input of a relay tester. The device uses a digital switch set between the A/D converter and the CPU of an electronic relay. The switch permits technicians and engineers to either pass data to the CPU from the system through the A/D converter or, by switching, feed the CPU data from the RAM, which has been loaded with the archived data. In this way, the relay system software can be examined and tested using actual event data under ordinary conditions as desired, with relay settings changed between tests to verify the efficacy of the changed settings to perform as desired for the recorded conditions. The digital switch can be either a hard-wired element, or can be a soft switch, operated through software instructions.