Partial Discharge Detection Using Ultra High Frequency In110kV XLPE Cable Accessories And Signal Propagation Properties

Partial discharge (PD) in high voltage cable accessories will producenanosecond steep pulse current and wideband UHF (Ultra High Frequency) signals.However, the UHF electromagnetic signals are difficult to radiate outward. UHFsignals will attenuate seriously when propagating along the cable core. The UHFsignals of PD are difficult to detect because of the metal shielding of joints whichwill absorb UHF signals.On the basis of signal propagation theory and R. Jobava’s numerical model ofimpedance distribution weighted parameter ratio of multilayer composite medium,UHF siganls generated by partial discharge propagate in cable and joints is studiedby using capacitor coupling method. The main research work is as follows:The theory of electromagnetic wave propagation in the UHF-range is given. Thereflection and refraction laws are discussed when electromagnetic waves from PDpropagate in composite medium layers. The attenuation of semi-conducting layer isspecially analysed. Amplitude attenuation of propagation characteristics could bederived by cable equivalent circuit and propagation formula. In order to analyze thepotential problems during the production and installation process, three typical defectmodels in110kV XLPE cable joint are desinged, using the finite element analysismethod. The defect’s position, size, shape and applied voltage are determined on thebasis of results of simulation. UHF partial discharge detection system is established,and the width of capacitance coupled sensor is determined by contrast experiment.UHF signals from PD of three typical models are dectected in the experiment system.Then the propagation characteristic of UHF signals are analysed. Pattern recognitionof UHF partial discharge signals is confirmed according to experiment data of threetypical defect models.