GB576708A - Apparatus for detecting faults in electric cables - Google Patents

Abstract

576,708. Detecting and locating faults. CALLENDER'S CABLE & CONSTRUCTION CO., Ltd., and GOODING, H. T. Sept. 6, 1944, No. 17066. [Class 37] Apparatus for the detection of an incipient fracture of a trailing cable conductor comprises means for making a circuit containing, in series, the conductor to be tested, a D.C. source, an inductive coil having an open iron core and capable of carrying a substantial current, an amplifier connected directly or indirectly across the coil, and a detector fed by the amplifier. The conductor 1 of the cable 2 is connected to terminals 4, 5 connected in series with a supply of direct current 3, and the primary winding 10 of a transformer 8 having an open iron core to avoid saturation by the direct current. The primary winding 10, which carries a heavy current, constitutes the inductive coil, the secondary winding 11 carrying a light current. A potentiometer 12 may be connected across the secondary winding, so that the input to an amplifier 9 may be adjusted. A neon lamp 13 is connected across the secondary coil to avoid excessive voltage at the telephone receiver 14, when the circuit of the inductive coil is made or broken. A1- ternatively a switch 15 in the primary circuit may be interlocked with a switch 16 in the secondary circuit, so that the latter is closed only after the primary circuit is made and is always broken in advance of the breaking of the primary circuit. A conductor of the cable to be tested is connected to the terminals 4, 5 and the cable is tapped vigorously at different points along its length ; if there is an incipient fracture, the resistance will be momentarily disturbed when the cable is struck near a break. This will cause an indication to be given at the output of the amplifier 9, resulting in a click or crackling sound being heard in the telephone receiver 14.