Determination of the optimum routine and selfchecking test time intervals for power system protection considering remote back-up protection system failure

In this study, routine and self-checking tests are performed as one of the methods to maximise the availability and adequate operation of power system protection. However, optimum routine test time intervals (ORTTI) and optimum self-checking test time intervals (OSTTI) should be determined exactly to anticipate maintenance cost of power system protection precisely. Back-up protection system failure has a vital role in determining precise ORTTI and OSTTI, whereas most of the previous studies have assumed that back-up protection system is perfectly reliable. Therefore in this study, an extended Markov model is proposed to determine the ORTTI and OSTTI by considering remote back-up protection system failure probability. It is worth noting that both self-checking and monitoring facilities that improve reliability of the protection system are considered in the proposed Markov model. Simulation results demonstrate that variations in reliability indices, ORTTI and OSTTI for power system protection are significant when remote back-up protection system is not fully reliable.