High Voltage Circuit BreakerHV AC Switchgear

Air break circuit breakers technical history in high voltage

Since compressed air has a higher dielectric strength and better thermal properties than air at atmospheric pressure, circuit breakers can be designed in high voltage. The air-blast principle is based on a blast of compressed air directed at the arc, preferably along its length, as an axial blast. This technology was, for more than 50 years, the technology for extra-high voltages until the advent of SF6 circuit breakers.
The development of the air-blast extinction principle started in Europe in the 1920s; further progress was achieved in the 1930s, and the air-blast circuit-breakers were widely installed
in the 1950s, having an interrupting capability of 63 kA that even increased to 90 kA in the 1970s.
The interrupters, however, have a relatively small dielectric withstand capability. This limitation comes from the opening speed of the contacts. The opening speed could be effectively increased by choosing multi-break designs. Therefore, an air-blast circuit breaker for rated voltages above 420 kV initially needed 10 or even 12 interrupters in series per pole.
Figure show Air blast circuit-breaker with 14 interrupters per pole for 765 kV in 1968 from ASEA.

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