Mov surge arrester's failure analysis

This paper provides catastrophic failure analysis of all three (3) station-class metal-oxide varistor (MOV) surge arresters located inside the metal-clad switchgear. All three surge arresters failed causing major damage to the switchgear without any evidence of switching surge activity. Analysis concludes that the B-phase surge arrester internal damage led to its thermal runaway. The exact cause of this arrester internal damage remains unknown. The passage of a ground fault current through the arrester damaged the mounting plate and the subsequent heat transfer caused the phase-phase-ground short circuit through the other arresters. All arresters and the switchgear enclosure were damaged. Investigation into the cause of these events is the subject of this paper. Evaluation of the existing power system configuration and arresters' installation inside the switchgear cubicle are included in the failure analysis. To minimize such failures, installation recommendations for the surge arresters inside the medium-voltage switchgear are also included in the paper.