GB716516A - Improvements in or relating to remote-control electric circuits - Google Patents

Abstract

716,516. Protective cut-out arrangements. ETABLISSEMENTS MERLIN & GERIN. Feb, 1, 1952 [March 6, 1951], No. 2708/52. Class 38(5). [Also in Group XXXVI] A cable 11 supplying apparatus 10 and comprising power conductors a, b, c. one or more pilot wires 1, each provided with an insulating sheath and embedded in a body 5 of conductive rubber associated with a metallic conductor 2, in the form of a sheath or sheaths coaxially about the insulation of the pilot wire or wires, is provided with a protective cut-out arrangement. A transformer 19 is energized when switch 8 is closed. and supplies alternating current to a rectifying circuit 24. Direct current flows in conductor 23 and potentiometer 25. The grids of an electron tube 27 are biased so that the direct current supplied by circuit 24 flows permanently in the circuit 26<SP>1</SP>, 26<SP>2</SP>, as long as the insulation,in the apparatus 10 and cable 11 is satisfactory, thus closing the contact 21 of relay 20. The circuit including the relay 13 is thus closed, and a small pulsating current permanently carried by the pilot conductor 1 thus flows through it, but is too small to close the contacts of relay 13. To energize the apparatus 10, a push button 15 is depressed, short-circuiting resistance 18. This creates a strong pulsating current which closes relay 13. Coil 12 is thus energized and contactors 9 closed. On releasing push button 15 the pulsating current falls to its initial value, which is sufficient to keep the relay 13 closed. In the event of an insulation fault in the apparatus 10, current flows through the supply line, point 29, circuit 33. resistance 44 and potentiometer 25 to earth. This causes a negative bias on grid G1 with respect to the cathode and thus interrupts the circuit through relay 20, opening contactor 21 and relay 13. Coil 12 is de-energized and contactors 9 open. An insulation fault in the cable 11 causes current to flow through the conductive sheath 5, conductor 2, circuit 28, resistance 46 and potentiometer 25 to earth. The grid 63 is biased negatively with respect to the cathode, interrupting the circuits through the relays and opening the contactors 9 as above. Specification 702,097 is referred to.