Showing papers by "General Cable published in 1967"

Discharge Detection in Extruded Polyethylene Insulated Power Cables

Abstract: An analytical study was made of the separator-filter type of discharge detector circuit when connected to long cable lengths during corona measurements of polyethylene insulated power cables. Based on this study, it is indicated how optimum detector and connecting circuit parameters can be chosen to best advantage when this type of detection equipment is used in factories where the electrical noise level is high. Under these conditions, it is indicated that a sensitivity of 4 pC (picocoulombs) is obtained on long lengths of power cables over a large range of commercial conductor sizes and voltage ratings; and that on relatively short lengths, the sensitivity is as low as 0.1 pC. It is explained that it is necessary to calibrate the particular measuring circuit with the cable load included, preferably using an exponential pulse applied to the far end of the cable, in order for the discharge measurements to have any real meaning.

Influence of space charges on the breakdown of oil-paper insulation

Abstract: It is a well-known fact that when some insulants under dc voltage are subjected to a polarity reversal, the breakdown immediately after the reversal may appear at a substantially lower voltage than the breakdown without polarity reversal. Since complete discharging of the sample does not occur after the polarity reversal, the voltage due to the charges remaining in the sample will add to the reverse voltage applied and will, in effect, increase the value of maximum stress in the sample. References 1, 2, and 3 consider the transient-stress distribution at the instant of polarity reversal in a cylindrical sample of oil-paper insulation subjected to temperature gradients. In their considerations, the influence of polarization on the maximum stress occurring immediately after a rapid polarity reversal is not taken into account and, as will be indicated later, this leads to substantial errors. The purpose of this paper is to establish the electrical strength of oil-paper insulation under rapid polarity reversals, with all space charges present in the insulation taken into account.