Electricians at Wolf Creek Power Plant complete fix on a differential

U.S. Army Corps of Engineers, Nashville District
Story by Mark Rankin

Date: 09.25.2013
Posted: 09.25.2013 13:22
News ID: 114246
Electricians at Wolf Creek Power Plant complete fix on a differential

JAMESTOWN, Ky. - The U.S. Army Corps of Engineers Nashville District employees from the Wolf Creek Power Plant and the Electronic Service Section have completed repairs to generator No. 3 following an electrical ground fault shutdown of the generator. <br /> <br /> “The fix has not been difficult, but it takes time making the repairs,” said Brent Thompson, a journeyman electrician at the Wolf Creek Power Plant. <br /> <br /> According to Thompson a differential electrical fault exists when a stator coil insulation fails in the unit that sends 13,800 volts to ground or phase-to-phase. Although this description is technical, the result is it causes the breaker to trip, which halts power generation. <br /> <br /> The Wolf Creek Power Plant is part of the Wolf Creek Dam on the Cumberland River. The power plant, which houses the hydroelectric generators, converts the mechanical energy of flowing water into electrical power. <br /> <br /> Thompson talked about the fault, “This was a much bigger spark than what is at your house, which is 120V. It shorted to ground then the relay sensed the path to ground and tripped off the unit, opens the circuit breaker and disconnects the power.” <br /> <br /> Differential protective relays serve as a fault-sensing element and control system for the generator and, in turn, disconnects the generator from the electrical power system.<br /> <br /> “This type of fault does not happen often,” said Thompson, “I’ve been here for 10 years and this is my first one.” <br /> <br /> He said the hardest part about the job was taking the time to analyze the damage, clearing and cleaning the unit, and identifying the location of the fault. <br /> <br /> “Fixing it and putting the unit back together again takes some time, but we’ll use this as training and experience for the crew,” said Thompson. <br /> <br /> After the mechanics and electricians removed the cover panels to the generator, they identify the problems visually within the unit. <br /> <br /> The next step is to contact Electronic Service Section which is located at Old Hickory Lake. The ESS analyzes the problem and stress tests the equipment by using computerized testing equipment to the fault and any additional damage to the unit. The electricians and electronic mechanics then evaluate how to repair the problem and complete the job.<br /> <br /> “Our job is to use computers and a vacuum circuit breaker to analyze current capabilities, stress test the equipment and learn where, when and all the failure points occurred based on the last date it was tested,” said Luke Ditto, an electronics mechanic in the ESS section. <br /> <br /> Power plants around the district share a generator stator coil repair kit, which has parts and items needed to make repairs quickly. <br /> <br /> “This has been a team effort and all goes well when we work as a team,” said Thompson. “Our goal is to simply get the unit fixed and back online as soon as possible.” <br /> <br /> The crew completed the differential fix and the unit is now back up and running smoothly. <br /> <br /> For current information about the U.S. Army Corps of Engineers Nashville District, visit the district’s website at www.lrn.usace.army.mil, on Facebook at http://www.facebook.com/nashvillecorps or Twitter at http://www.twitter.com/nashvillecorps.