Con Edison has been conducting a thorough review of events that led to a large power outage this past Saturday on the West Side of Manhattan in New York City. The outage started at 6:47 p.m. EDT, and the lights were back on shortly after midnight. At its height, the number of customers out reached approximately 72,000. They were concentrated in an area that reached West 72nd Street on the north, West 30th Street on the south, the Hudson River on the west and 5th Avenue on the east.
According to Con Ed, an inspection of equipment and preliminary review of system data indicate that the relay protection system at the West 65th Street substation did not operate as designed. That system detects electrical faults and directs circuit breakers to isolate and de-energize those faults. The relay protection system is designed with redundancies to provide high levels of reliability. In this case, primary and backup relay systems did not isolate a faulted 13,000-V distribution cable at West 64th Street and West End Avenue.
The failure of the protective relay systems ultimately resulted in isolation of the fault at the West 49th Street transmission substation, and the subsequent loss of several electrical networks, the statement read.
"Based on our experience with the transmission and distribution system, we initially believed the 13,000-volt cable fault was unrelated to the transmission disturbance. While the cable fault was an initiating event, the customer outages were the result of the failure of the protective relay system."
Con Ed's investigation has involved inspecting and testing transmission equipment, and analyzing the large volumes of data. "Through this work, we determined that the outage was not caused by transmission equipment. Further analysis identified the issues with the relay protection system."
Con Ed said the analysis of data and testing of the relay protection equipment is continuing, and will provide more insight into why the system, and its multiple redundancies, did not operate as designed.