Patent GB-438139-A (GB)
Title: Improvements in distance relay mechanism for the protection of electrical installations
IPC: H02H7/30
Filed: 1934-05-12
Abstract: 438,139. Protective cut-out systems. WIDEROE, R., 36, Borgenveien, Vindern, near Oslo, Norway. May 12, 1934, No. 14435. [Class 38 (v)] In a distance relay of the kind wherein a short-circuiting current, acting through the intermediary of a magnetically - saturated current transformer, heats a thermic element producing a force proportional to the squareroot of the short-circuiting current and tending to release the relay and increasing with time, this force being opposed by another force depending on the voltage to be dealt with in such a way that the relay operates when the first-named force predominates, in order to prevent upsetting of the time-lag by vibrations set up by A.C. in the armature of the voltage coil, the latter is fed by D.C. preferably produced by rectifying the voltage of the voltage-transformer. The latter, shown at 27 in Fig. 1, feeds the voltage coil 33 over a rectifier 15 and a shunt rectifier 16 allows current to flow through the coil due to its self-induction during the part of the wave when 15 is non-conducting. The coil may be connected directly to capacitative voltage couplings 17. In Fig. 2, the coil is in two halves 45, 46 energized by rectifiers 18, 19 so arranged that the halves are alternately energized during the cycle. In Fig. 3, (not shown), the coil is connected across a full-wave bridge. Where it is desired to alter the release characteristics of the relay from the normal curve b in Fig. 5, the voltage coil is energized also by a current proportional to the line current. According as this assists or opposes the voltage effect the curve c or a is obtained. Fig. 4 shows a method of carrying this into effect, the terminals 27 supplying the voltage effect and an auxiliary transformer 50 the current effect. The voltage coil is in two halves 45, 46 and a shunt impedance 52 with a midpoint tap is provided. With the direction of the rectifiers shown, a characteristic corresponding to curve a is obtained, but by reversing the directions of rectifiers 47, 48, a characteristic corresponding to curve c could be obtained. The characteristic could further be made dependent on the direction of flow by, for instance, short-circuiting transformer 50 by means of a directional relay to obtain characteristic a or b, and by removing the short to obtain characteristic c. In Figs. 6-10 (not shown), are other connections for obtaining the latter characteristic. Fig. 11 shows a complete system using a directional relay to vary the characteristic. The current coils 54 of the directional relay and the primary of the auxiliary transformer 50 are in the primary circuit 4 of the intermediate transformer and normally shorted by contacts 2 of the overload relay 1. The directional relay contacts 49 are in circuit with rectifier 47 and the secondary of 50 across the halves 45, 46 of the voltage coil energized from transformer 27 over rectifiers 18, 19. A neon lamp 55 serves as an indicator of the line voltage and of the soundness of the voltage circuit of transformer 27. In a polyphase relay only one set of contacts 49 is used to control the several voltage coils and their transformers 50, Fig. 12 (not shown). The rectifiers are preferably of the dry-surface type.