Discussion at Pacific Coast convention

J. S. Thompson: I would like to have you consider what we believe is a step in the right direction in regard to oil circuit breakers. Our factory has developed an oil circuit breaker with six breaks per pole, which is not a new idea at all. We have done it in a novel way in that we have not increased the number of pieces of insulation between the conductors and the ground, but have simply introduced an auxiliary insulation between breaks. This auxiliary insulation is far from sufficient to maintain itself against the line´s voltage, but it is only subjected to an impressed voltage at the instant during which the breaker is between theclosed and the open position; it is of baklite and relatively small andfailure of this auxiliary insulation simply would cut out certain of thebreaks in the circuit. We have such an installation on a 60,000-volt line. This breaker after breaking thirteen short circuits produced by the test of various fuses which failed to open the circuit, was then tested on direct dead short circuit. After having been tested once with no evidence of any form of distress, the engineers took the bold step of putting this breaker on the loaded system of the Pacific Gas & Electric Company which was at that time being contributed to by Pit River, Drum Electra, Oakland and San Francisco. The breaker was subjected to short-circuit operations with this power concentrated on it (though I will have to say that the power was brought to this distributing point by a 110-kv. systemand transformed to 66-kv.), so you will see that the breaker was put to a thorough test. It operated at 2000 amperes, which immediately dropped to 1350 or 1400. A Westinghouse relay closed the circuit in about five cycles and then there were consumed ten cycles for the mechanical operation of the tripping coil, and the movement of the blade out of contact, and nine cycles of diminishing amperes while the arc was being drawn thenfive cycles between the rupturing of the arc and the- end of the travel of the oil circuit breaker.