Behavior study of polarized distance relay in presence of the simultaneous faults

The first part of the paper is concerned with an algorithm of fault calculations for several cases of simultaneous faults to obtain complete information about the current and voltage which are needed in power network protection systems, especially distance relays. The second part presents the behavior of plain and polarized distance relays for each fault case and deals with the operation caused by simultaneous faults. It is shown that any distance relay protection scheme used can lead to incorrect operation in the presence of simultaneous faults. Finally, some modifications in distance relays must be provided to satisfy the requirements of the corresponding simultaneous faults.