Fast bus transfers for open phase analysis at nuclear power plants

The open-phase condition has received regulatory and industry scrutiny in recent years, following the course of events that took place at the Byron nuclear power plant in Illinois, in 2012. Open-phase events, when undetected in a timely manner, can be detrimental to motors; and therefore, could result in loss of safety functions that are necessary for ensuring safe plant shutdown. Advances have been made in the area of detection of the open-phase condition, via implementation of various relaying schemes. The relays provide the mechanisms for actuating circuit breakers, and isolate auxiliary loads in the event of an open-phase protection trip. Load isolation generally consists of transferring the loads from the faulted source to a healthy source. Load transfer can be accomplished through different transfer schemes; however, this paper will focus on the Fast Bus Transfer method, as it is the most common transfer type at nuclear power plants. Using the Electromagnetic Transient Program - Restructured Version (EMTP-RV), this paper addresses a fast bus transfer scheme from a primary source of power to an alternate source, following an open-phase protection trip, and compares to a non-open phase transfer.