The performance of high-voltage oil circuit-breakers incorporating resistance switching

The paper reviews the improvement obtained in the performance of side-vented explosion pots when they are shunted by resistors. First, it is shown that the rating of explosion pots is determined by two critical regions, one of which determines the maximum voltage rating, whilst the other determines the maximum breaking-current rating. The effect of resistors on these critical regions is first described and then illustrated by actual test results. Secondly, it is shown that the resistors shunting the pots can also be used to give even voltage-distribution over several pots in series. The application of resistors in practice is illustrated by the description of a 132-kV oil circuit-breaker rated at 2,500 MVA. The effect of the resistors when breaking small currents in inductive and capacitive circuits is discussed in detail. A discussion follows on the validity of testing separately one pole of a 3-phase separate-tank breaker, having two breaks per pole, by applying the full 3-phase output of the test plant, the third Jerminal being obtained by bringing out through the tank wall a connection from the moving cross-bar. In conclusion, actual performances are illustrated by test results obtained on one pole of a 3-phase, 132-kV, 2,500-MVA breaker.