Con Edison Statement
Con Edison has been conducting a thorough review of events that led to Saturday’s outage on the West Side of Manhattan. 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. 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 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, starting at 6:47 p.m.
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 systems.
From the moment the event began, we focused on restoring customers safely and quickly. More than half of the customers were restored in under three hours and all within five hours. Once we restored customers that evening, we immediately turned to determining the cause of the outage.
Our 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.
We have restored our system to its normal state to continue providing our customers with the high level of reliability they expect and deserve. Our 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. We will share additional information as it becomes available.