Prolonging Periodical Testing Intervals of Numerical Protection Relays

The paper describes the principles regarding periodical testing of protection relays in the Finnish national grid. Three internal utility studies aiming at prolonged test intervals are presented. The first is an analytical study for modernisation of relay testing procedures, the second is a reliability centered maintenance (RCM) analysis for protection and, finally, the third is a fault and risk analysis with reliability calculations. Based on these three studies, a decision was made to prolong the periodical test intervals, but only of modern numerical protection relays.