PROPAGATION OF WIDE BAND SIGNALS IN POWER CABLES (PARTIAL DISCHARGE, CROSS CORRELATION, SEMICONDUCTING LAYER)
Abstract
A systematic investigation of propagation of wide band signals in solid dielectric power cables has been done in this thesis. This work is directly useful for detection and location of partial discharges in such cables. It may also find other applications to, for example, power system communication, control and protection. As the first step of the investigation, the dielectric properties of semiconducting layers in several typical cables have been measured in frequency band 15 KHz - 50 MHz. The measurements have shown that these black semiconducting materials have very large dielectric constants and loss tangents. And these dielectric properties are strongly dependent on frequency. At very high frequency (50 MHz), the dielectric constants are still much larger than those of cable insulations and the loss tangents are close to 1. With the dielectric data provided by the cable manufacturers or by the measurements mentioned above, the propagation constants for single phase solid dielectric cables having various configurations have been computed in a very wide frequency band. The formulas used in these computations are derived directly from the Maxwell equations. Computation results show that semiconducting layers have significant influence on the propagation constants, at least in the frequency band higher than 10 KHz. With the propagation constant obtained by the computation mentioned above, partial discharge waveforms received at terminals of a cable have been computed. Investigating the calculated results, it has been concluded that if the cable length is not too short, the waveforms generated by partial discharges are not important for detection and location of them. Only three parameters defined as the direct component, delay time and rise time of a partial discharge wave can characterize is properties. In order to locate and detect a partial discharge in a cable, cross correlation type instruments have been developed in recent years. theoretical computation of the cross correlation function of the signals received at two terminals of a cable has been done in this thesis. This computation may be useful for developing the instruments and analysis of their measurement results.
Degree
Ph.D.
Subject Area
Electrical engineering
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