Switching in Electrical Transmission and Distribution Systems

7 Gas Circuit-Breakers

7.1 Oil Circuit-Breakers

From a historical perspective, oil circuit-breakers were the first circuit-breakers designed for high-power applications. The interruption of current in oil circuit-breakers is performed in oil by way of the dissociation product H₂ gas (see Section 6.3), and therefore the oil circuit-breaker is classed as a gas circuit-breaker. At the beginning of the twentieth century, their breaking capacity was sufficient to meet the demands of the power systems at that time. Oil circuit-breakers are still used in the electrical power system worldwide, but development stopped long ago.

Oil circuit-breakers are classified according to the volume of oil used: bulk-oil and minimum-oil circuit-breakers.

Bulk-oil circuit-breakers (see Section 6.3.2 for the interruption principle) were of simple design: a set of contacts immersed in oil and not equipped with interruption chambers. One of the first plain-break circuit-breakers in the USA was designed and built by J.N. Kelman [1] in 1901. It was capable of interrupting a short-circuit current of 300 to 400 A at 40 kV supply voltage. Kelman's circuit-breaker (Figure 7.1) was made up of two open wooden barrels filled with a combination of water and oil. The two breaks, connected in series, were operated by a common handle. This circuit-breaker was in service for less than a year, from April 1902 to March 1903, and after a number of current interruptions at short-time intervals, blazing oil was spewed ...