Development of The SF6 Circuit Breakers

Three types of SF6 Breakers Two Pressure Gas Breakers Puffer Gas Breakers Arc Assisted / Self Blast Puffer Gas Breakers

Two Pressure Gas Breakers First Developed in 1960s Resembled double pressure air blast breakers Have a sealed gas system with a gas compressor Usually have an air compressor for the operating mechanism SF6 gas is stored at high pressure (250 psi) in storage tanks.

Two Pressure Gas Breakers Gas storage tanks require heaters and insulation due to the fact SF6 liquefies at a relative high temperature Breakers may be live tank or dead tank Breakers may gang operated or independent pole operated Breakers require the use of a blast valve

Two Pressure Gas Breakers Two pressure gas breakers are mechanically very complex. Two pressure gas breakers require significant maintenance There is high pressure gas (250psi) as well as low pressure gas (85psi)

Westinghouse SFA Two Pressure Interrupter

Operation of The SFA Interrupter

Single Pressure Gas Breakers Also known as puffer breakers No gas compressor required Gas interrupter chamber contains gas at approximately 75psi Are mechanically much simpler that two pressure breakers Single pressure gas breakers require significant less maintenance than two pressure breakers

Two Pressure & Single Pressure Animation Puffer Operation 1 Puffer Operation 2

Arc Assisted Or Self Blast Breaker Current breaker design Simpler and smaller with even greater interrupting ability Uses the heat energy of the arc to create the high pressure stream of gas for arc interruption

Arc Assisted Or Self Blast Breaker Includes a mechanical puffer piston for switching low grade faults and load currents where there is not enough heat to create the high pressure gas stream needed

Overview The arc assisted puffer breaker or “self blast” breaker is the 3rd generation of SF6 gas breakers The self blast breaker is designed to use the heat from the arc to supply the blast pressure that extinguishes the arc during faults with higher current This reduces the amount of operating energy needed for breaker operation. The operating mechanism now only needs to supply the energy needed to move the contacts

Advantages of Self Blast Breakers The cost of the operating mechanism is reduced because it can be made smaller than before The reliability is improved because there is less chance of mechanical failure from moving the bigger mechanical parts in earlier style breakers

ABB Self Blast interrupter chamber

High Fault Currents During very high fault currents the arc will build enough pressure to close the self blast valves, preventing gas from flowing into the puffer volume. This forces the gas to flow through the nozzle and extinguish the arc

Low Grade Faults During lower fault currents the arc will not build enough pressure to close the self blast valves and the interrupter will act like a puffer breaker

Self blast interrupter cycle for high current faults