Thesis

The excitation of UHF signals by partial discharge in gas insulated substations

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Awarding institution
  • University of Strathclyde
Date of award
  • 1996
Thesis identifier
  • T8733
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Abstract
  • This work is an investigation of the ultra-high frequency (UHF) signals excited by partial discharge (PD) sources inside gas insulated substations (GIS). PD is indicative of defects in the insulation system and by using couplers mounted at intervals along the GIS, the corresponding bursts of UHF signal can be extracted. This is the principle of the UHF monitoring technique used for detection and identification of insulation defects in GIS. UHF diagnostics are the most useful of a range of techniques for PD detection that are reviewed. The UHF technique is compared with conventional PD measurements, illustrating the requirement for a study of the fundamental aspects covered in this research. Current pulses from a test cell containing a needle PD source are measured using a transient digitiser with an analogue bandwidth of 1GHz. A scheme for injecting calibrated repetitive pulses to simulate PD and excite similar UHF signals is presented. Waveguide transfer functions are derived that relate the electric field at a remote UHF coupler to the current flowing at the PD source by using the dyadic Green's functions for cylindrical and coaxial configurations. These expressions are implemented in a computer simulation of the theoretical model. Experiments that validate the model are described and it is used to predict the effect of various PD parameters on the UHF signal. As a result of this research, the excitation of UHF signals by PD currents (previously understood only in general terms) can now be quantified. A scheme for standardising UHF measurements of PD in GIS is suggested, based on the improved understanding of the processes involved. This would ensure that a GIS monitoring system is designed with adequate sensitivity to detect a critical defect. Possible topics for future research based on the theory developed in this work are discussed.
Resource Type
DOI
EThOS ID
  • uk.bl.ethos.606331
Date Created
  • 1996
Former identifier
  • 500615

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