Patent GB-225283-A (GB)
Title: Improvements relating to electrical relays
IPC: H02H3/40
Filed: 1923-08-28
Abstract: 225,283. Conwell, R. N. Aug. 28, 1923. Induction relays have a plurality of core members provided with two primary windings energized from separate sources of power which with co-operating secondary windings are arranged to produce a rotating field in a predetermined direction for actuating the movable relay element in a direction corresponding to predetermined relative values or directions of the currents in the primary windings. In the form shown in Fig. 1 the two alternating- current sources S<1>. S<5> supply the primary windings X<1>, X<5> of the two transformers T<1>, T<5> wound on magnetic core limbs L<1>, L<5>. On these limbs are also wound secondary windings Y<1>, Y<5> supplying oppositelywound series-connected pairs of windings OW<1>, OW<5> on other limbs OL<2> OL<4>. Normally when the current sources S' S<5> are equal the disc G is stationary but a torque is produced on the disc in one direction or the other by the interaction of the fluxes due to the currents in the primary and secondary windings in correspondence with the predominance of one of the current supplies S', S'. In the modified form of relay shown in Fig. 2. the sources S<6>, S<7> supply series-connected pairs of primary windings X', X<7>.on the limbs L<1>, L<5>, these coils assisting on the latter and opposing on the former limb. Secondary windings Y<1>, Y<6> supply windings OW<1>, OW<5> on limbs OL <2>. OL<4> as before. Normally the disc G has a torque in one direction but if one of the supply sources S<6>, S' is reversed the torque, undergoes a corresponding reversal. A further form of relay shown in Fig. 4 has two sources of supply connected between terminals S<8>, S<9> and a common terminal SM. This terminal is connected through a coil X<1> on limbs L' to the junction of two coils X<6>, X<7> on limb L<2> the other ends of which go to terminals S<9>, S<8>. Secondary circuits are similar to those in Fig. 1. Normally the current from sources S', S<9> circulates through windings X<6>, X' in series no current flowing through the winding X<1> and a torque is produced on the relay disc G. If one source undergoes a reversal the current in winding X<6>, X<7> no longer circulate but oppose each other, both passing through the winding X'. A consequent reversal is produced in the torgue on the disc G. Similarly a predetermined predominance of one of the sources S<8>, S<9> without reversal, the excess current passes through the winding X<1>, which is arranged under these conditions to have a larger number of ampere-turns than the windings X<6>, X' so that torque reversal in the disc G again occurs. To vary the restraining torque or bias and consequently to vary the magnitude of unbalance at which this torque reversal occurs, the lead 20 from the winding A<1> to the coils X<6>, X<7> may alternatively be connected at points 21 or 22. Fig. 5 shows the above form of relay with modified secondary connections, the windings Y<1>, Y<5> instead of feeding separate, pairs of windings OW<1>, OW<5> on limbs OL<2>, OL<4> are connected to a common pair of windings PW carrying the difference of the two secondary currents. A similar modification of Fig. 1 is also described. The disc 9 besides operating contacts may be arranged to operate a pointer or recording device. Protective arrangements.-When applied to the protection of parallel feeders, Fig. 7, two relays R', R<5> are each supplied with currents from series transformers CT<1>, CT<5> in each feeder K<1>, K<5>. The discs G', G<5> carry contacts M<1>, M<5> which are held by spring 13 away from fixed contacts N<1>, N<5>. When the current in one feeder, for example K<1> exceeds that in the other by a predetermined amount, the torque in relay R<1> rotates the disc G, joining contacts N<1>, M<1>, and completing the circuit of the trip coil TC<1> controlling the circuit breaker CB'. At the same time the opposite torque produced in the disc G<5> merely reinforces the pressure of the spring 13. A similar arrangement of relays is described in the protection of a 3-phase motor, the relays being fed from potential transformers and operated on disturbance of the voltage balance between the phases. In Fig. 9 a relay R has its windings SP and SC fed from potential and current transformers PT and CT in the stator circuit MP of an induction motor. When the heavy starting current has fallen sufficiently. the predominance of the source SP causes engagement of the relay contacts, completing the circuit of the coil CS which moves over a spring-controlled switching bar, closing switches C' - - C<3> which short-circuit starting resistances SR in the rotor circuit MS. In Fig. 10 is shown a section SG<1> of the switch gear in a loop main fed from generators, one of which OK<11>is shown. One primary coil SP<1> of the relay R' is fed from a potential transformer PT<1> and the other' SC<1> from a current transformer CT<1>. When the current exceeds a predetermined value, the consequent predominance of the source SC<1> over the constant source SP<1> causes a reversal of torque in the relay R<1>, completing the tripping circuit of the interrupter CB<1>. Other similar switch gear units are installed throughout the system.