GB600733A - Improvements in or relating to fluid blast electric circuit interrupters, having arcextinguishing means - Google Patents

Abstract

600,733. Oil-break switches. WESTING HOUSE ELECTRIC INTERNATIONAL CO. Dec. 15, 1944, No. 25194. Convention date, Dec. 15, 1943. [Class 38 (v)] The charging current of a H.T. circuit is interrupted by a circuit-breaker comprising, in the example shown, contacts 22, 34, 36, for establishing a pressure-generating arc and an interrupting arc, and means are provided for lengthening the interrupting arc to a predetermined length while minimizing the fluid-flow towards the arc, and then suddenly applying a strong fluid-flow after the arc has attained its predetermined length. Contacts 22, 36 are held closed against the action of springs 45, 65, by an insulating rod 31 engaged by one end of a bridging member 8 adapted to bridge two similar structures 7, Fig. 1 (not shown). The contacts 22, 36, are also urged together by springs 27 compressed between a plate 30 on rod 31 and nuts 28 on rods 26 secured to extensions 24 of contact 22. A casting 15, in which contact 22 is pivoted 'at 23, carries an insulating plate structure similar to that described in Specification 571,091, the platecontours of which are illustrated in Figs. 4 to 18 (not shown) and provide vertical oil passages 125, 140, and horizontal blast entry and exhaust passages 106, 141. A plate 111 supports a cylinder 117 co-operating with a piston 127 which is spring-urged downwards. The lower end of contact 36 is connected to rod 31 by a parallel-motion linkage passing through the slotted lower end of a cylinder 129 which is slidable inside the piston 127 and relatively to the contact 36 and urged downwards by springs 115 to abut on the member 8. The breaker is opened by lowering the member 8, allowing the rod 31 to follow, taking the contact 36 with it, Simultaneously, contacts 22, 34, are opened forming two series arcs 35, 37, Fig. 3. With heavy loads or short-circuits, the oilpressure due to the arc 35 extinguishes the arc 37 and also prevents piston 127 from moving down. When the pressure has diminished, the piston 127 moves down to flush out the arcing region. Should the current be a charging current, however, after the contacts have opened, the cylinder 129 is driven down by springs 115 and, after a time delay, a flange 130 thereon moves the piston 127 down to cause an extinguishing oil blast across both arcs. This time delay is chosen between certain limits. The earliest limit is ¢ cycle before a total contact separation is reached sufficient to withstand double normal peak voltage applied to the separation when filled with clean oil. The latest limit is that time in the contact stroke corresponding to a contact separation at which, without pumping, arc re-strikes during charging current interruptions take place after zero current pauses of as long as <1>/3 cycle. The bridging member 8 engages resilient contacts 58 on the rod 31, the opening movement of which is damped by a dashpot 68 comprising a piston 72 which is caused by a nut 71 to force oil through apertures 75 thereby cushioning the opening stroke. A spring 74 returns the piston 72 to its upper position. A high resistance 81 is connected between the casting 15 and an electrostatic screen 120 in order to equalize the voltages across the units 7 and reduce the residual current to be broken at contacts 8, 58. The Specification sets out in detail, accompanied by curves, the theory governing the operation of the pumping arrangement. In a modification, Fig. 19 (not shown), the time delay is derived from byepass passages in the cylinder 117 allowing an initial free descent of the pumping piston.