GB815479A - Improvements in or relating to protective arrangements for electrical systems, such,for example, as tachometer generator systems - Google Patents

Abstract

815,479. Protective cut-out systems. GENERAL ELECTRIC CO. Ltd. Oct. 5, 1956 [Oct. 5, 1955], No. 28405/55. Class 38 (5). A protective arrangement includes a valve oscillator for injecting a testing current into a circuit through resistance and capacitor and a potentiometer chain for detecting change of voltage across the resistance for tripping or signalling when the circuit impedance exceeds a certain value. The circuit normally operates on D.C. or on A.C. at a frequency lower than that of the oscillator. A direct current tachometer generator 1 driven by a machine shaft 2 feeds a potentiometer 4 in a servo control amplifier 3. An auxiliary current from a valve oscillator 7 is fed into the armature at 5, 6 through a resistance 8 and a capacitor 53 from a transformer 10 with a swamping resistance 14 across its secondary. An amplifier-detector 11 responds to the voltage across the potentiometer chain 21 which is across the resistance 8 so that a set drop in this voltage will result in the operation of a relay 12 which can shut down the apparatus on which the tachometer is fitted. The setting at which the relay 12 operates is adjusted by a potential divider 23 with a metering jack 24 in series. In Fig. 2 (not shown), the same protective circuit is applied to a trolley driven by a motor fed from trolley wires with a second set of trolley wires for an interlocked brake circuit.