Con Edison: Recent customer outages caused by failure of protective relay systems

The company said that based on its experience with the transmission and distribution system, it initially believed that the 13-kV cable fault was unrelated to the transmission disturbance

Consolidated Edison Company of New York on July 15 said that failure of the protective relay systems resulted in isolation of the fault at the West 49th Street transmission substation and the subsequent loss of several electrical networks, which started on the evening of July 13, and left about 72,000 customers without power.

As TransmissionHub reported, Con Edison on July 14 said that it restored power to all affected areas on the west side of Manhattan shortly before midnight.

“Our inspection of equipment and preliminary review of system data over the past 40 hours indicates that the relay protection system at our West 65th Street substation did not operate as designed,” the company said in its July 15 statement. “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-volt distribution cable at West 64th Street and West End Avenue.”

The company said that based on its experience with the transmission and distribution system, it initially believed that the 13-kV 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 systems, Con Edison said.

The company noted that more than half of the customers were restored in under three hours and all within five hours.

“Our investigation has involved inspecting and testing transmission equipment and analyzing the large volumes of data,” Con Edison said. “Through this work, we determined that the outage was not caused by transmission equipment. Further analysis identified the issues with the relay protection system.”

In a separate July 15 statement, New York City Mayor Bill de Blasio said, in part, “While I appreciate that Con Edison released their preliminary findings so quickly, I am troubled that one of the few factors Con Edison initially ruled out, the 13,000 volt cable, has been determined to be the catalyst of the outage.”

He added that “we will continue to push Con Edison for a full accounting of this incident to ensure they are taking necessary steps to protect all New Yorkers.”

Con Edison said in its July 15 statement that its analysis of data and testing of the relay protection equipment is continuing, and that it will provide more insight into why the system, and its multiple redundancies, did not operate as designed. The company noted that it will share additional information as it becomes available.