Patent GB-499329-A (GB)
Title: Improvements in or relating to alternating current electric relays
IPC: H02H3/40
Filed: 1937-07-22
Abstract: 499,329. Protective cut-out arrangements ; electromagnetic relays. REYROLLE & CO., Ltd., A., LEYBURN, H., and FREELAND, C. July 22, 1937, No. 20327. [Class 38 (v)] A mechanically-balanced directional A.C. relay comprises a movable contact-member subjected to two opposed forces respectively dependent on the vector-sum and the vectordifference of two alternating quantities representative of main circuit characteristics, as current and voltage, and means for so controlling at least one of such representative quantities that, irrespective of relatively wide variations in the magnitude of the characteristic it represents, the said quantity is always of substantially the same order of magnitude as the other representative quantity. In Fig. 1, two groups of coils E, F and E<1>, F<1>, act on opposite ends of a balanced beam D, the coils E, E<1> being energized in accordance with the current flowing in phase A, and the coils F, F<1> with the voltage between phases A, C. Assuming a phase-rotation A, B, C and unity power factor, the current in coil E<1> leads by 30 degrees that flowing in coil F<1> with normal direction of power-flow, and the vector-sum of the fluxes produced by these currents acts in the restraining direction to maintain contacts D<2> open. The coil E is connected in the opposite sense to E<1>, so that the currents in E, F are 150 degrees phase - displaced, and the vectordifference of the fluxes due to them acts on the beam in an operating direction. When the power-flow is in the normal direction, the relay is held inoperative, but when the flow and hence the current-direction in E, E<1> reverses, the operating force is produced by the vectorsum and the restraint by the vector-difference, and the relay operates. The coils E, E<1> are connected to phase A over a transformer G which is arranged to be nearly saturated at normal load, so that the increase in current supplied to E, E<1> on overload is only small. By connecting in shunt to coils F, F<1> a choke which, under normal conditions, is saturated and then has a low impedance compared with that of F, F1 combined, and by connecting an impedance in series with the combined coils and choke, the voltage-drop across the coils may be arranged, when the line-voltage falls to 10 per cent normal, only to fall to a third of its normal value, Fig. 2 (not shown). Induction-disc or other relays may replace the beam-relays of Fig. 1, and a relay is provided for each phase. Quantities which combine to produce the opposed forces may be injected into two opposed coils acting on a relaycontact as in Specification 413,723, or, as shown in Fig. 3, at E, F, E<1>, F<1> into summation transformers S, T, the secondaries of which energize windings of shaded-pole magnets W, X, acting on an induction-disc V. In Fig. 4 (not shown), a relay is adapted for directional earth-leakage protection by connecting its " voltage " coils to a saturable transformer energized by a current-transformer in the neutral, or an artificial neutral, connection. The current-coils are energized as in Fig. 1 and the arrangement operates with earth-fault and reversal of current-direction in the phase of the circuit protected. Fig. 5 shows an arrangement in which an additional restraint against operation is provided, whereby the relay does not operate unless a ratio generally representative of fault-distance is below a given value. Coils F, F<1> are energized in dependence on voltage B-C, and a condenser P and resistance P<1> are provided to give the current a lead on the voltage, the latter being in quadrature with the phase A current in coils E, E<1>. The impedance coils N, N<1> are connected in series with an inductance R to voltage A-C, and interact with coils F, F<1> to provide a restraint due to the vector-sum, and an operating force due to the vector-difference of their fluxes. On fault between phases A, C, the current in N, N<1> diminishes, and with it correspondingly the restraint. On power-reversal, the required operating-current depends on the value of the restraint and is less the lower the restraint. The two coils N, N<1> may be replaced by a single coil acting on the beam in a restraining direction, Fig. 6 (not shown). Such a relay is applicable as an initiating relay in the impedance-protective system described in Specification 320,968, [Class 38 (v)]. Instead of saturable transformers or chokes, resistances varying with temperature may be used, and the Specification refers also to quantities derived from different main circuits.