GB1508352A - Cable fault location - Google Patents

Abstract

1508352 Locating faults in cables ELECTRICITY COUNCIL 16 Jan 1976 [17 Jan 1975] 2239/75 Heading H4D Apparatus for locating a fault in a conductor of a cable comprises an impulse generator with connecting means for applying a voltage step impulse between the conductor to be tested and a return conductor, a waveform display or recording device and linear coupling means having a primary winding in series with the connecting means and a secondary winding connected to the display or recording device whereby a voltage signal dependent on the rate of change of current in the connecting means is displayed or recorded thereby giving an indication of the fault condition of the cable. In Fig. 1, the cable under test 10 has an inner 11, and an outer 12, conductor, conductor 12 being earthed. Low resistance or high resistance faults between the conductors and open circuit may be detected by connecting the fault location apparatus to the conductors 11 and 12. High voltage D.C. source 14 charges capacitor 16 via resistor 15. Switch 17 connects the high voltage side of the capacitor via co-axial connector 18 to inner conductor 11. The other capacitor terminal is connected via the primary winding 19 of the linear coupling transformer 20 and the connector 18 to the earthed conductor 12. Linear coupler 20 further comprises a secondary winding 21 one end 22 of which is connected to earth and to an electrostatic screen 25, the end is connected, in shunt with damping resistor 26 to oscilloscope 24. Circuit 21, 26 is effectively a highpass filter. The differentiated current waveforms resulting from various faults in the form of spikes, whose amplitude and spacing is indicative of the range and type, e.g. a flashing intermittent fault, as sensed in winding 21, are displayed on oscilloscope 24, which may have storage facilities. Details of typical waveforms are given (Figures 3(a)-3(e), not shown).