Public Service Company of New Mexico (PNM) on Dec. 13 told the New Mexico Public Regulation Commission that it plans to acquire, replace, and install four 115-kV circuit breakers in the Albuquerque area.
The breakers will be replaced with “new 63 kA breakers” at PNM’s West Mesa 115-kV switching station to ensure continued reliable operation of PNM’s 115-kV system in the Albuquerque area, as well as to capably interrupt increased fault current on the transmission system, the company said.
The project has an estimated cost of about $1.2m, and a targeted completion date of August 2018.
The company also noted that the breakers being replaced have reached the end of their useful life, approaching 50 years of service. Replacement parts are no longer available from the manufacturer and the time to locate replacement parts from other utilities, or to repair existing parts, could lead to extended outages and jeopardize the reliable operation of the system, PNM said.
Annual technical studies conducted to determine which breakers are approaching their capacity limits have shown that the growth-related transmission and generation additions in the Albuquerque metro area have caused an increase in available fault current on the 115-kV transmission systems, the company said.
The available fault current is exceeding the fault current momentary rating or interrupting rating on four breakers at the West Mesa switching station during normal system operating conditions, and as a result, the breakers are undersized for the interrupt requirements of the existing system based on the manufacturer’s design limits, PNM said.
Exceeding the design ratings can lead to failure of the breaker to clear a fault with consequences ranging from larger customer outage impacts to catastrophic equipment failure, the company said.
The new breakers will effectively ensure continued safe and reliable operation of the breakers for the expected fault current at North, Person, Sandia, Reeves, and West Mesa stations, the company said.