Apparatus to measure continuously corona inception and extinction voltages in movinginsulated cable cores

摘要

1,201,801. Testing cable insulation. GENERAL CABLE CORP. Sept.14, 1967 [Sept.20, 1966], No.41904/67. Heading G1U. A cable testing apparatus is of the type where the cable 1 is passed through an elongate fluid bath probe 11, and potential gradients are established along the probe between a central electrode 8 supplied with high alternating voltage and earthed end electrodes 10, two detector electrodes 12, 13 being situated symmetrically relative to the central electrode near each end of the probe. The ratio of the output pulse amplitudes obtained at the two detector electrodes indicates the position along the probe at which a corona discharge occurs within the cable, and this position indicates the corona inception voltage. To render the result independent of pulse shape, &c., the detector electrodes are coupled by a capacitor stack C5 whose electrical centre is connected to the central electrode 8, and the signals derived from the detectors are passed through the filter rectifier-amplifier chains 25A- 28A, 25B-28B, that from one electrode 14 being inverted, and applied to opposite ends of a multitapped resistor R5. The particular tapping at which zero amplitude voltage occurs along this resistor is determined and represents the corona inception voltage. To determine the position along the multi-tapped resistor where zero volts occurs, trigger circuits 33 are attached to repective tappings. The number of these which are triggered indicates the required position. This number is determined by parallelling the trigger output currents to flow through a resistor 36, the voltage across this indicating the number. This voltage, representing the corona voltage, may be displayed on an oscilloscope 40, or used to control an alarm 42 and a recorder 43.