GB598581A - Improvements in or relating to electric protective arrangements for sectionalised a.c. circuits - Google Patents

Abstract

598,581. Protective cut-out systems. REYROLLE & CO., Ltd., A., LEYBURN, H., LACKEY, C. H., and TOWNS, D. H. Aug. 8, 1945, No. 20337. [Class 38(v)] A protective arrangement for a sectionalised A.C. circuit comprises at each end of the protected section, a transmitter F acting on fault to send to the remote end of the section a h.f. current modulated in accordance with the secondary output of a saturable transformer D, whose primary is fed from line current transformers B1- B3, and a receiver K for demodulating the h.f. current from the remote end, tripping means being responsive to the phaserelationship between the outputs of the receiver and the saturable transformer for cutting out the section at the adjacent end the section preferably being cut out at both ends on an internal fault whether it is fed from one or both ends. The secondary winding D1 of the saturable summation transformer D is connected through a filter E, which provides a uniform standard wave form, to a h.f. transmitter F set in operation by a further winding D2 of transformer D, so as to feed modulated h.f. current into the section through coupling condensers H and a filter L, which also prevents this current from reaching the adjacent receiver K. The latter receives the modulated h.f. sent from the far end, demodulates it, and passes the output through a saturable filter M to a comparison circuit in which it is compared with the output of the adjacent transformer D in series in the grid circuit of a valve N. On an external fault, the outputs from the secondary D1 and the receiver K are in phase-opposition so that the grid of valve N remains negatively biased. With an internal fault fed from both ends, however, the two outputs are additive and the anode current of the valve receives an A.C. component which energises the tripping relay P through a transformer O. With an internal fault fed from one end only, the grid of one valve N receives only the transformer output, and the other grid receives only the transmitted output, but each output is arranged to be sufficient to produce tripping at that end. In modifications, Figs. 2-4 (not shown), the outputs are applied to the relay P via circulating- current or opposed-voltage circuits, or fed into two balanced windings of the relay or of a transformer energising the relay.