Patent GB-453525-A (GB)
Title: Improvements in or relating to electric protective arrangements
IPC: H02H7/22
Filed: 1935-03-14
Abstract: 453,525. Protective cut-out systems. REYROLLE & CO., Ltd., A., Hebburnon-Tyne, and LEYBURN, H., 212, Wingrove Road, Newcastle-on-Tyne. March 14, 1935, No. 7896. [Class 38 (v) A discriminative protective arrangement for the individual sections of a network to which a number of feeders or external circuits are connected, comprises a directional relay for each circuit responsive to the direction of fault current therein, means for cutting out the section controlled by the relays, and means controlled by the relays for preventing the section being cut out, the arrangement being such that the section is not cut out if the direction of fault current flow in any one circuit is different from the direction of fault current flow in any other circuit. The Figure shows the application of the invention to a duplicate bus-bar system wherein external feeders or other circuits A can be connected to either bus-bar set B, C, through breakers D and selector switches E, F and the bus-bars can be coupled by means of a breaker G<1>. Each feeder A has a core-balance or current transformer arrangement H, the secondary output of which corresponds to the earthleakage current in the feeder. Each secondary is connected in series with one winding K<1> of a directional relay K across the bus-wires J, J<1> The second coils K<2> of the relays K may be energized either by the system voltage or by the total leakage current. In the latter case, they are connected in series or, as shown, in parallel, across J<1>, J. A master relay L may be connected in series with the windings K<2> or, as shown, in parallel, across the bus-wires. The relays K close trip contacts K<3> when the flow is towards the bus-bars, and lock-out contacts K4 when the flow is away from them. The bus-bar coupling G has an earth-leakage transformer arrangement G<2> energizing the coil M<1> of a directional relay M, the coil M<2> of which is in series or parallel with the coils K<2>. The contacts M<3>, M<4> of this relay control, respectively, the lock-out relays Q, P, which, when operated, at once break at Q<2>, P<2> the circuits to the coils of the trip relays O, N, associated with the sets C, B, respectively. The trip relays N, O operate with a time-lag contacts N<2>, 02 controlling the trip coil G4 of the coupler-breaker G<1> and the trip coils D<1> of the breakers D in the feeders. The selectors E, F have contacts E<1>, Fl for connecting the contacts K<3> to the bus-wire N<1> or O<1> associated with the appropriate trip relay N or O, and contacts E2, F<2> for connecting contacts K4 to the buswire P<1> or Ql associated with the appropriate lock-out relay P or Q. Further contacts E<3>, F<3> ensure that the trip coils D<1> are connected to the contacts of the appropriate relay N or O. On external earth faults, the current entering the bus-bar system balances that leaving the system, and the relay L remains unoperated so that its contacts L<1> remain open. If a fault occurs on the system B when the coupler G<1> is open, relay L closes its contacts and the relays K of the feeders connected to the faulty system close their contacts K<3> to energize relay N and isolate that system. If B is faulty when coupler G<1> is closed, the relays K of the feeders associated with the healthy bus-bars C also close their contacts K<3>, but disconnection of bus-bars C is prevented by operation of relay M to energize the lock-out relay Q. Where feeders are interconnected at their remote ends, contacts D<2> operated by opening of a breaker D due to a fault in a feeder, between its breaker and the transformers H, close a pilot circuit S to disconnect the remote end and prevent the fault being fed therefrom. If in such fault condition, the breaker D is disconnected from both busbars, switches E4, F4 directly connect contacts K<3> to the pilot S and effect tripping of the remote breaker. The Specification refers also to interphase faults, to the use of a current relay for closing the contacts K<3> and a directional relay contact constituting the lock-out contact K4 and to the use of summation transformers in cases where the feeder transformers are of unequal ratios.