GB380808A - Improvements in or relating to protective cut-out systems - Google Patents

Abstract

380,808. Protective cut-out arrangements. WESTINGHOUSE ELECTRIC & MANUFACTURING CO., East Pittsburg, U.S.A.-(Assignees of Bergvall, R. C. ; 321, South Avenue, Wilkinsburg, Pennsylvania, U.S.A.) June 17, 1931, No. 17572. Convention date, June 19, 1930. [Class 38 (v).] In a protective system for a section with circuit-breakers at each end, and associated fault-distance-responsive relays, the latter being responsive only to faults within a predetermined distance less than the distance between the two stations, from the relaying point, when a circuit-breaker is tripped at one end of the section a tripping impulse is sent either directly through pilot wires or indirectly by superimposed high-frequency currents to cause the simultaneous tripping of the circuit-breaker at the other end of the section. As shown in the Figure, lines 4, 5 are branched off from a busbar system through 6 circuit-breakers 7, 8. At each circuit-breaker location are an instantaneously-operating fault relay 12 associated with directional elements 50, 51 and instantaneously-operating interphase impedance relays 13, 15, 17 and 19, 21, 23 for the respective lines fitted with opposing voltage and current coils 41, 40 so that they become operative with interphase faults within a predetermined distance along the line which is less than the distance between the stations at its ends. When the circuits of tripping coils 9, 10 of circuit-breakers 7, 8 are completed through circuits 65, 66 or 67, 66 impulses are sent through a pilot-wire circuit 70 to cause the simultaneous tripping of the circuit-breaker at the other end of the affected line, a polarized relay 77 discriminating between the impulses for the different lines 4, 5. To prevent incorrect tripping due for example to inductive disturbances in the pilot wire circuit faultdetector interlock contact relays 84, 85 are provided and are arranged to lock the polarized relays 77 out of action until a fault of some kind occurs on the system. Overlap impedance relays 14, 16, 18 and 20, 22, 24 are also provided for dealing with faults beyond the range of the relays 13, 15, 17 and 19, 21, 23, these relays operating the tripping circuit at the end of time periods imposed by timing devices 54 which are set in motion by the corresponding overlap relays, the latter being energized by suitable opposing voltage and current coils. In a preferred modification, Fig. 2, (not shown) the tripping impulses between the ends of the circuit-breakers are conveyed by suitable H.F. currents superimposed on the lines, different frequencies being employed for impulsing in opposite directions. In a further modification, Fig. 3 (not shown), H.F. tripping impulses are sent through a pilot wire which may form a portion of a telephone cable, in which the D.C. impulses employed in Fig. 1 would travel too slowly to give satisfactory operation. The circuit-breaker in these modifications is provided with back contacts to cut off the supply of H.F. current after tripping has occurred. In order to ensure tripping of the circuitbreaker if any fluttering of the tripping relay occurs during response, the circuit-breaker trip coils in these modifications are shunted bv resistances so that during response of the tripping relays the current builds up rapidly in the tripping circuit to a value sufficient to maintain an arc across the relay contacts during any momentary break periods which may occur at the contacts during response.