Patent GB-481152-A (GB)
Title: An improved electrodynamic relay for the protection of electrical installations
IPC: H02H3/40
Filed: 1937-08-31
Abstract: 481,152. Induction relays; protective cut-out arrangements. LANDIS & GYR AKT.-GES. Aug. 31, 1937, No. 23773. Convention date, Sept. 9, 1936. [Class 38 (v)] In an induction-type tilting relay for protective purposes, the tilting member controlling the contacts comprises at least one short-circuited frame energized by a transformer, the frame being controlled by at least one coreless field coil system producing two fields acting in opposition to one another. In the simple excess-current relay shown in Fig. 1, the coils 3, 4 of the field coil system are connected in series with a primary winding 7 mounted on a transformer core 6, and are energized from a current transformer 1 on the network 2. The short-circuited frame 5 acting as the secondary winding of the transformer forms one limb of a tilting member 8, the other limb of which is acted on by a spring 9 and carries a bridging contact 10. When excess current flows through the network the turning moment due to the field system overeomes the force of the spring, and tilts the member 8 to close at 11 the circuit of the trip coil 12 of a circuit-breaker 13 in the network 2. By arranging that the turning moment due to the coils normally overpowers that due to the spring, the device may be made to act as an under-current relay, and if the coils are energized from a voltage transformer instead of a current transformer, the device acts as an over- or under-voltage relay. The responding value of the relay may be varied by adjusting the tension of the spring, and the spring may be replaced by a weight or by an electrical opposing force. If the coil 7 and the coils 3, 4 are respectively connected to different linked voltages of a three-phase network, the device may be used as a symmetry relay. By connecting the coils 3, 4 to a current transformer and the coil 7 to a voltage transformer, or vice versa, the device may be made to act as a directional relay, in which the trip coil circuit is energized on a reversal of current flow in the network 2. In the arrangement shown in Fig. 3, which acts as a resistance relay, the coils 3, 4 and 7 are connected in series and energized from a current transformer 1, and an additional field coil system, comprising coils 15, 16 energized in parallel from a voltage transformer 17, is provided for controlling the short-circuited frame 5. On the occurrence of a fault in the network 2, the current rises and the voltage drops, so that the turning moment of the coils 3, 4 overcomes that of the coils 15, 16 and the frame is tilted to close the circuit of the trip coil 12. In the arrangement shown in Fig. 4, the device acts as a currentcomparison relay, the coils 3, 4 being connected to a current transformer 1<1> in the conductor 2<1>, while the coils 15, 16 are connected to a current transformer 1<11> in the conductor 2<11>. The coil 7 is energized by a voltage transformer 17, which may be energized from the bus-bars 2<111> or from any other voltage source. Each of the circuits connected to the current transformers 1<1>, 1<11> includes the winding 20 of a differential relay 23, which is arranged to close its contacts 22 in the event of a short-circuit or excessive overload in one of the conductors 2<1>, 2<11>. In such event the frame 5 then moves to close the circuit of one of the trip coils 121 or 12<11> through contacts 11<1> or 11<11> and the contacts 22 of the differential relay, and the defective conductor is disconnected from the bus-bars. In a modification, Fig. 5 (not shown), two short-circuited frames are provided, the primary windings of which are energized from the current transformers. An impedance relay with two short-circuited frames 5<1>, 5<11>, forming the secondary windings of transformers 61, 6<11> is shown in Fig. 6. The prinary winding 7<1> of one transformer is connected in series with the field coils 3, 4 to a current transformer 1, and the primary winding 7<11> of the other transformer is energized in parallel with the field coils 15, 16 from a voltage transformer 17. By arranging the contacts 10 on the left-hand side of the tilting member, instead of on the righthand side as shown, the device can be made to act as an admittance relay.