Patent GB-191516053-A (GB)
Title: Automatic Protective Gear for Electrical Systems.
Inventor: ROSENBAUM MOSES ROSENBAUM COMM
IPC: H02H3/16
Filed: 1915-11-13
Abstract: 16,053. Rosebourne, [formerly Rosebaum], M., and Couse, F. A. Nov. 13. Protective arrangements. - The bus - bars 2, 3, Fig. 1, of a system are connected together through resistances 6..9, an intermediate point 10 of which, constituting an artificial neutral point, is connected to earth through the conductor 11. When a fault to earth occurs on any of the conductors of the system, the resulting current in the conductor 11 operates a discriminating relay 12, which shortcircuits a portion 7 or 8 of the resistance, so that the earth conductor is no longer connected to a neutral point, and the increased current which flows through the fault unbalances the currents in the feeders 4, 5 to such a degree that a differential relay 31 associated with the feeders will close the trip coil 33 of a circuit-breaker 32 and cut out the feeder on which the fault occurs. In place of short-circuiting a portion 7 or 8 of the resistance, the relay may operate to shift the point of connexion of the earth conductor from the neutral point. The relay 12 closes the contacts, 14, 15 or 14, 16, according to the direction of the current in the earth connexion, and completes a circuit from the bus-bars to the operating-coils 17 or 18 of the short - circuiting switches 19, 20. When the resistance 7 or 8 is short-circuited, the relay is de-energized, but the short-circuit is maintained by the hold-on coil 21 or 22 acting on switches 25 or 26 and connected across the contacts 14,15 or 14, 16, thereby preventing sparking. In the arrangement shown in Fig. 2, the resistance 7 is replaced by the lamps 36, 37, the resistance 8 by the lamps 39, 38, and the resistances 6, 9 by the single resistance 41 in the earth conductor 11. The lamps, when extinguised by short-circuiting, indicate the occurrence of a fault. The hold-on coils in this arrangement are directly connected in circuit with the short-circuiting switches 19, 20. A fuze 40 with a time-lag, or a time-limit relay, is included in the earth connexion adapted to operate only after the feeder circuit-breaker operates. For alternating currents, the resistances are replaced by reactances. The cut-out arrangements described are applicable to a split-conductor system with feeders 44, 45 and 46, 47 supplied from both ends, as shown in Fig. 3. Double-pole circuit -breakers are provided at each end of the feeders with trip coils 50, 51 controlled by differential relays 52 .. 55 connected to shunts in the split conductors so that the circuit-breakers are operated if the requisite unbalancing, produced as described in connexion with Fig. 1, occurs in either pair of conductors constituting a split conductor. The application to a three-wire direct-current system is similar, the resistances 7, 8 are not equal, so that the earth conductor is not connected to a neutral point, the unsymmetrical connexion allowing of a current flow in the earth connexion when a fault occurs on the middle or neutral conductor of the threewire system and consequently, operation of the relays when a fault occurs thereon. By combining the arrangement last described with that shown in Fig. 3, the invention may be applied to a three-wire network having split-conductor feeders which can be supplied with energy from either end, and the neutral conductor may, in this case, be under the control of a hand-operated knife switch.