GB740411A - Improvements in or relating to electric protective and control apparatus - Google Patents

Abstract

740,411. Protective cut-out arrangements. SIEMENS - SCHUCKERTWERKE AKT.- GES. July 9, 1953 [July 9, 1952], No. 19072/53. Class 38(5) In a control and protective arrangement, e.g. for use with mining installations, D.C. sources 5, 6 having voltages of different magnitudes are connected in opposition at the ends of a pilot conductor 8 and an earth conductor E, a polarized relay 4 being connected in series with the pilot conductor adjacent the lower voltage source 5 and control switches 10a, 10e being associated with the higher voltage source. In Fig. 1, on the depression of the "on switch" 10e, current flows from the higher voltage source 6 through the relay 4 which closes contacts 12 to effect the closing of a circuitbreaker 2. A relay 14 is now energized and closes contacts 13 to maintain the pilot circuit closed when the switch 10e is released. In the event of a short-circuit between the conductors 8, E, current flows from the source 5 in the reverse direction through the relay 4 and fault path 7 and the relay 4 closes contacts 11 to effect the opening of the circuit-breaker 2. The D.C. sources may be batteries as shown, but rectifier arrangements may be used, Fig. 2 (not shown). Alternatively, charged condensers may be used as the higher voltage source, the condensers being initially charged from the low voltage source and subsequently maintained charged by a rectifier arrangement supplied from the power conductors, Figs. 3 and 4 (not shown). The higher voltage source may only be connected to the conductor 8 during the actual closing operation of the circuit-breaker 2. In this case, the relay 4 controls the circuit-breaker through a relay which completes a holding circuit for itself when energized, Fig. 6 (not shown). When the supply is from a transformer having its star point connected through a resistor to the conductor E, the relay 4 may be arranged to produce tripping on fault between a main conductor and the conductor E, a by-pass circuit for the alternating current being provided, Fig. 5 (not shown).