Anatomy of a complex electrical failure and its forensics analysis

This paper depicts an accident that happened in 2010 in a Brazilian Chemical Plant. A combination of different events, installations and commissioning errors coupled with equipment failures involving the primary substation, resulted in catastrophic failure. A single phase failure of a 138 kV disconnect switch, during closing, initiated events and phenomena that resulted in a complete plant shut down. This paper will walk the reader thru the events, forensics analysis as well as power system analysis that allowed the authors to identify what happened, how it happened and what to do to prevent it from happening again. The paper will show how the anatomy of the problem, involving equipment failure, single phase arcing, switching transients, overvoltage, capacitive coupling, transferred surge voltages, ungrounded system, transient overvoltage due to an arcing ground fault on an ungrounded system, insulation coordination, flash-over and lack of adequate surge protection. All of which resulted in a catastrophic failure of an arc resistant switchgear and a serious arc flash incident. The research followed some steps that will be commented here as well as the lessons learned.