Root cause investigation of the inadvertent failure of unit 2 forced draft fan motor and the corrective actions implemented

In today's competitive power generation market place, reliability and availability of auxiliary motors is critical to the operation of the power plant. Thermal degradation of the winding insulation of high voltage motors has prompted us to consider ways to monitor the condition of the insulation of the winding of our 4160V critical motors. This is because the forced draft fan motor 2B inadvertently failed due to the destruction of a section of both the winding and the laminated core of the motor which set the motor into flames. The machine environment creates several mechanisms that can age the stator insulation. In addition to electrical and mechanical stresses, heating of the insulation due to copper losses in the conductor is an important thermal aging factor, especially in conjunction with differential expansion forces experienced by conductor and insulation, leading to a progressive degradation of the electrical insulation. Many insulation failures originate with aging that occurs over many years. To operate cost effectively, means to periodically assess the condition of insulation of the winding are needed. This paper provides the root cause analysis of the inadvertent failure of Unit 2B Forced Draft Fan Motor and the steps taken to correct the failure and the implementation of the corrective actions. The analysis also showed that out of the six potential causes, three of them are the most likely causes and they are thermal aging, operator's failure to heed to the manufacturer's hot start and cold start timing sequence and excessive heat due to poor maintenance work on cleaning and changing the filters.