Junk Plant Wolf Creek: Appalling Sense of Safety with Emergency DG

Power Potential Transformer Overloading Results in Emergency Diesel Generator lnoperability

On October 6, 2014, at approximately 1326 Central Daylight Savings Time (CDT) during a scheduled 24-hour Run, the 'B' Emergency Diesel Generator (EOG) unexpectedly tripped and a fire was observed in the electrical cabinet (NE106). This resulted in an unplanned entry into a 72 hour shutdown Limiting Condition of Operation (LCO) and an ALERT emergency classification. The source of the fire was the Power Potential Transformer (PPT). On 1/28/16, a Hardware Failure Analysis concluded that the failure of the PPT was most likely due to overloading which resulted from failure of a diode in the power rectifier of the EOG excitation system. Failure of the diode mostly likely occurred during load transients on June 11, 2014. 

The station did not have the ability to assess the degradation of the PPT within the EDG's excitation system that led to the continual operation of a degraded component, resulting in significant equipment failure. Additionally, there were limited preventative maintenance, obsolescence issues that had not been addressed, limited knowledge of the exciter, and the design of the system lacked overcurrent protection/detection of the PPT. The station continued using the PPT after it was identified as degraded on June 11, 2014. When the smoking was first identified, the PPT was determined to be degraded, but could still perform its safety function due to the EDG satisfactorily performing its surveillances. 

The 'B' EOG was most likely inoperable from June 11, 2014 until October 9, 2014. During that time period, the 'A' EOG was taken out of service for maintenance on July 21, 2014, creating a condition where both trains may have been inoperable. When the 'A' and 'B' EDGs are inoperable, there are no remaining safety related on-site stand-by AC…