Patent GB-363005-A (GB)
Title: Improvements in or relating to protective equipment for electrical distribution systems
IPC: H02H7/26
Filed: 1930-09-18
Abstract: 363,005. Protective cut-out arrangements. WESTINGHOUSE ELECTRIC & MANUFACTURING CO., East Pittsburg, U.S.A.-(Assignees of Crichton, L. N. ; 61, South Munn Avenue, East Orange, New Jersey, Graves, H. C. ; 124, South Lynn Boulevard, Highland Park, Upper Darby, Pennsylvania, and Feldmann, M. R. ; 293, Chestnut Street, Nutley, New Jersey, both in U.S.A.) Sept. 18, 1930, No. 27905. Convention date, Sept. 18, 1929. [Class 38 (v).] A protective arrangement, particularly for multitrack railways in which trolley conductors 12,12<1>, 12<11> are in parallel between bus-bars 15, 16 of transformer stations 17, 18 supplied from a single-phase H.T. line 11, is provided with means for compensating for the reduced impedance of the load circuit which arises when a high impedance fault occurs at times of heavy load. Each conductor has two breakers 13, 14 and each breaker is provided with a relay system similar to that shown for the breaker 14 of the line 12. A current transformer 37 supplies the current windings 35, 41, 48 in series of, respectively, a presetting element 31, an instantaneously-acting impedance relay 27, and a directional relay 28, whereas a voltage transformer 38 supplies the voltage winding 36 of the element 31 and the restraining element 42 of the relay 27. The element 31 acts to adjust a resistance 32 in series with the restraining element 42 of relay 27 so as to increase the restraint with increasing load. A reactance 39 and condenser 40 are provided so that the element 31 exerts its maximum torque when the phaseangle between the current and voltage in line 12 is 60‹, and an autotransformer 46 is provided for adjusting the setting of the impedance relay 27, the current coil 41 of which is shunted by an impedance 47 for byepassing the D.C. component of an asymmetric fault. The restraining element 42 of relay 27 is in two parts one of which includes a reactance 421 so that the resulting phase-displacement of the flux in the two paths ensures that there is always some restraining flux. The coils 49 of the directional relay 28 are energized in series with corresponding coils of the relay of the adjacent section from current transformer 50 in the bus-bar 16, the windings 48, 49 being arranged to operate the relay 28 only when current in excess of a predetermined amount flows from the bus-bar 16 to the line 12. Thus, if a heavy current flows from line 12, say, to the bus-bar 16 to feed a fault in line 121 or 1211 only the relay 28 in the faulty line will operate. With a fault of predetermined severity, relays 27, 28 both operate to close the circuit of trip relay 54 through their series-connected contacts 44, 45, 52, 53 and armatures 43, 51, with the result that the trip-coil 26 of the breaker of the faulty line is energized and the line cut out. To avoid the difficulty of an impedance relay 27 being unable to discriminate between a fault near the far bus-bar 15 of its own section and a fault near the bus-bar 15<1> of the next section, the relays 27 are adjusted to work only up to 90 per cent of the length of the section. A fault within the last 10 per cent would open the breaker 13, but the fault would still be fed from the near end. The breaker 14 is, however, tripped by overload relays 29, 30, the former being instantaneous in operation with high setting, and the latter acting, with a lower setting after a timedelay due to an inductance 59 and further relay 58 An indicator 56 is also provided.