Patent GB-521074-A (GB)
Title: Improvements in or relating to protective arrangements for electrical distribution systems
IPC: H02H7/26
Filed: 1938-11-18
Abstract: 521,074. Protective cut-out systems. WHIPP & BOURNE, Ltd., and WHIPP, F. Nov. 18, 1938, No. 33507. [Class 38 (v)] Discriminative protection of the sections of a d.c. circuit 16, sectionalized by means of breakers A .. D having contacts .17, holding windings 28, and economy resistances 19, as described in Specification 214,667, [Class 38 (v)], is obtained by current - responsive directional relays each associated with a breaker and comprising a current-energized iron circuit adapted, when the current is excessive, to move a permanent magnet and attached switch arm 26 one way or the other in dependence on the direction of flow. Normally contacts 20, 21, 22 are closed by the bridge-members 23, 24, 25 and springs 27, but if a fault occurs at 31, members 26 to the left of the fault move to the right, so opening contacts 21, 20 whereas the members 26 to the right of the fault move to the left and open contacts 21, 20. The holding-coils 28 of breakers A, D are kept energized by the contacts 22, 20 of the relays of breakers B, C, respectively, over the leads 30, but the coils 28 of breakers B, C are de-energized at their own contacts 21 and at contacts 20, 22 of the adjacent relays, and so the faulty section is isolated. Extension-of the fault-damage to the wiring 30 does not impair the protection, since the contacts at the ends of both the conductors 30 at the fault are open. In a modification, Fig. 3 (not shown) designed to obviate the drawback of lack of voltage on fault, a shunt circuit is arranged about each of the coils 28, and its lower resistance 19 and contact 21, and each is adapted to be closed by an overload contact, the arrangement being such that the breaker-coils 28 on either side the fault are open-circuited and release at once, whereas the coils 28 of the breakers A, D are shortcircuited, but do not open at once, as explained in Specification 521,073, and their relays restore when the fault is cleared at breakers B, C. In a modification of this last arrangement, Fig. 4, the overload contacts of the shunt circuit are incorporated at 35 in the directional relay, and the members 23.. 25 of each relay are fixed to the arms 26. Normally all the contacts of each relay are open, but on fault at 31, contacts 22, 35 of relays at A, B close, as also contacts 20, 21 of relays at C, D, thus short-circuiting all the coils 28. The coils of breakers B, C' are shortcircuited through the lower resistances 19, but in the case of breaker A, the shunt circuit about 28 includes the conductor 32, contact 35, bridge 24, and conductor 16, bridge 25 of the B-relay, and conductor 30, and a similar circuit can be traced for the coil of D through the contact 23 of the, C-relay As pointed out in Specification 521,073, the decay of the flux in the coils 28 of breakers A, D is slower than that of the coils of breakers B, C which isolate the fault and cause the restoring of the relays at A, D. The Provisional Specification describes a directional relay in which the permanent magnet has its poles located near to, and on opposite sides of, a reduced section of a copper bar serving as current-conductor, so as to swing in one direction or the other when the current exceeds a given value.