Determining the faulted phase

In August 1999, a lightning strike caused a misoperation of a relay installed in the late 1980s. The relay misoperation caused a two-minute outage at a petrochemical plant and led to an exhaustive root-cause analysis. The misoperation can be attributed to incorrect fault type selection in a distance element-based, 1980s-era relay. Two separate events in different locations, one in December 2007 and another in March 2009, highlight additional incorrect operations that occurred due to the same problem and root cause. The recent events remind us that this topic is still important and should be reviewed. This paper shares details about three challenging case studies and their root causes. Methodical root-cause analysis techniques are used, including mathematical simulation and testing of old and newer relay designs. This paper contrasts distance and fault identification algorithms, demonstrates methodical analysis techniques, and proposes solutions. Fault type selection logic is discussed, and the evolution and improvement of faulted phase selection logic over several decades is demonstrated. A newer relay design, available since 1993, is proven to have improved performance, namely better security, for these challenging cases.