Technologies for Improved Reliability of Shielded Power Cable and Characterization of Capacitor Film Energy Density

Date of Completion

January 2010

Keywords

Engineering, Materials Science

Degree

Ph.D.

Abstract

Partial Discharge (PD), a partial breakdown of insulation between high voltage electrodes, reduces cable reliability. Understanding electromagnetic propagation of PD-induced pulses in shielded power cable, including attenuation and dispersion, is essential to the application of PD diagnostics and, especially, PD location. Dispersion is caused by the transition of cable semicon-ducting layers (between the cable conductors and dielectric) from "resistive" at low frequency to "capacitive" at high frequency. Methods are presented to compute dispersion as a function of semiconducting material properties and evaluate the effect of dispersion on pulse characteristics (amplitude, shape, and width, etc.) as a function of distance propagated, the results of which are applied to investigate the effects of dispersion for PD detection and location. The location error induced by dispersion can be compensated from calibration. ^ Electrochemical degradation of cable dielectrics, known as "water treeing", is one of the leading cause of premature failures in underground shielded power cable. Silane-based fluid has been used successfully for decades to rejuvenate HMWPE and XLPE dielectric cables to "cure" existing water trees and extend cable life. However the ability of the treatment to inhibit future water tree initiation is not known. A method for silane fluid treatment of un-aged cable insulation and semicon was developed based on the use of GC/MS to determine curing of the fluid within the dielectric. A wet electrical aging test at 5 kV/mm (127 V/mil) based on a sample which includes semicon electrodes on both sides of the XLPE insulation with a water electrode in contact with one semicon layer was used to age untreated samples, samples treated prior to the test, and samples treated at the mid-time of the test (3500 hrs). The result of aging is analyzed by microscopic examination to determine the number, length and types of water trees. The mechanism by which the silane-based fluid cures existing water trees and impedes the formation of future water trees is addressed.^ To characterize polymeric capacitor film, a solid state, high voltage switch rated 8 kV with a turn-on time in the range of 100 ns and current capability from μA to kA was developed based on the use of two SCR's in series. The system is used to measure energy release from linear and nonlinear dielectrics as a function of discharge time constant. Sufficient current is injected into the gates of the SCR's that the switch operates well from μA to kA with low current turn-on duration in the range of a second.^

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