GB910396A - Method of, and means for, testing a pair of conductors in an electrical system - Google Patents

Abstract

910,396. Protective arrangements. LUCAS (INDUSTRIES) Ltd., JOSEPH. Sept. 1, 1961 [Aug. 9, 1960], No. 27534/60. Class 38 (5). [Also in Group XXXVI] In a method of testing for the presence of open- or short-circuit faults on a pair of conductors 3, 4, Fig. 1, for example, for connecting a control device 5 to an instrument 6, signals from a continuous-wave or pulse generator are supplied to one end of the conductor 3 and at the other end are supplied with phase reversal via transformer 19 to the other conductor 4, which, at the control end, is connected to a phase detector, Fig. 2. Inductors 13 ... 16 prevent the signals reaching the control device and instrument. In the event of a short-circuit, a phase change in signals fed to conductor 4 is prevented and an alarm is given by the detector. Similarly, an alarm is given if due to open circuit no signals arrive at the detector. In the absence of faults the signals received at input terminals C, D of the detector are of equal amplitude and similar phase and transformer 31 provides no output. At the same time signals from generator 7 and supplied to terminal A, Fig. 2, render transistors 57, 61 conductive and cause illumination of alarm lamp 62. In the presence of a fault, however, a signal at terminal D is absent, or is reversed in phase or is reduced in amplitude with the result that the transformer 31 provides an output which is amplified by transistor 41 and rectified in diode 65 which by virtue of the signal applied at terminal B is rendered phase sensitive. The rectified voltage renders transistor 50 conductive and cuts off signals from terminal A to render transistors 57, 61 non-conductive. The lamp 62 is thus extinguished to signify a fault. A separate detector may be used to detect possible failure of capacitors 12, 34.