GB557940A - Improvements in or relating to electric circuit-interrupting arrangements - Google Patents

Abstract

557,940. Protective cut-out arrangements; mercury switches. ELECTRICAL IMPROVEMENTS, Ltd., and GREGORY, R. W. June 9, 1942, No. 7860. [Class 38 (v)] A circuit-interrupting arrangement comprises a pair of switch elements A, B connected in series, the element A being shunted by a fuse C of high rupturing capacity. Operation of protective relay E energizes the trip coil A<SP>1</SP> of element A, which opens the short-circuit about the fuse C, causing the latter to blow if the current is sufficient; otherwise the circuit is opened by element B, the trip coil B' of which is energized after a time-delay by a relay D energized simultaneously with A<SP>1</SP>. The elements A, B may be combined into a single structure having three fixed contacts and a single movable contact which may be pivoted, Fig. 2 (not shown), or in the form of a bridge-contact as in conventional oil switches, Fig. 6 (not shown). An opposed-voltage, Merz-Price protective system may have the trip relay in each of the three phases of the pilot circuit controlling such a unitary circuit-breaker at each end of the feeder, Fig. 7 (not shown). In Fig. 5, a body of mercury normally interconnects contacts H, H', H<SP>2</SP>, but when the coil J is energized, the hollow plunger J<SP>1</SP> is lifted to break contact between H, H' and finally, if the fuse C fails to blow, between H, H<SP>2</SP> when the mercury has run out of aperture J-.