Replacing SF6 gas circuit breakers on New York’s transmission system

One of the six 115,000-volt vacuum circuit breaker (VCB) installation pilot projects has been successfully completed in Cortland, Tilden, Whitehall and New Scotland substations, and there more are on the way.

Two more pilot installations are due to take place, in addition to over 100 vacuum circuit breakers that will be installed as part of the Upstate Upgrade.

This successful completion also proves that we have the technology to replace SF6 gas circuit breakers on the 115kV transmission system.

An integral part of our electrical grid

The circuit breaker is an integral part of our electrical grid and is a critical component of operating safely and reliably.  

Since the 1980s, sulphur hexafluoride (SF6) has been the industry accepted standard insulator for high voltage circuit breakers, due to its excellent dielectric strength and arc quenching ability. However, SF6 is an extremely potent greenhouse gas - it’s around 24,300 times more effective at trapping infrared radiation than an equivalent amount of CO2.

In New York State alone, National Grid has over 1,000 high voltage circuit breakers containing SF6.  Reducing emissions by replacing leaking SF6 equipment is an important part of our goal of reaching net zero.

Historically, VCBs have only been used at voltages below 40,000 volts.  The VCB uses a vacuum bottle to interrupt the current and insulate between the contacts, with pressurised air surrounding the vacuum bottle isolating the energised parts from the case of the circuit breaker.  

Due to technological advancements, VCBs are now available with ratings up to 145kV. With a technology that uses air and vacuum instead of SF6 gas, we are demonstrating a new solution to reduce our SF6 emissions on the 115kV system with the VCB pilot program.

Hero photo caption:

Photographed above are operations personnel in front of National Grid’s first Vacuum Circuit Breaker installed on the 115kV transmission system. Listed from left to right: Kyle Pierce, Radomir Pupovac, Barbara Battaglia, Scott Dahlin, Matthew Witherell, Gregory Distin, Eric Lindsley Noah Christensen, Jacob Romancik. Not pictured: Aubrey Borgesi and Crystal Cook.