GB858332A - Improvements in and relating to electrical protective relay devices and protective relay systems incorporating such devices - Google Patents

Abstract

858,332. Protective cut-out arrangements. ENGLISH ELECTRIC CO. Ltd. April 18, 1957 [April 23, 1956], No. 12307/56. Class 38 (5). [Also in Group XXXIX] The coupling between primary and secondary windings on a transformer core is controlled by driving the core to saturation by means of a control winding such that the varying differential permeability of the core effective in coupling the primary and secondary windings is wholly or substantially that of the region beyond the knee or knees of the B-H loop of the core. The control winding may have a D.C. bias sufficiently large not to permit A.C. in the primary winding to reduce magnetization to the knee of the B-H loop. Alternatively the control winding may be energized with A.C. of an amplitude sufficiently large to ensure that the core spends only a small time in any cycle in switching between the saturation regions. The construction of core preferred is one of four limbs with the primary and secondary windings at opposite ends of and wound to embrace both central limbs while the control winding is in two halves, one on each centre limb, wound so as not to be coupled with the primary and secondary windings. The core material is lowloss silicon steel. As applied to a protective relay system for a power line 20, Fig. 3, the control winding 24 is energized with D.C. proportional to the voltage on the line while primary winding 22 is supplied with a current proportional to that across the line. The differential permeability of the core in the region beyond the knee of its B-H loop is substantially hyperbolically-related to the control flux so that the output induced in secondary winding 23 is proportional to the admittance of the line and when this reaches a predetermined maximum the output operates a circuit-breaking relay 29. By omitting the rectifier 28 and the smoothing circuit 31 alternating current of an amplitude proportional to that across the line may be applied to the control winding to produce the same result except that the admittance at which the circuit-breaker operates varies with the phase angle between current and voltage on the line.