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Title: Comparative laboratory performance characterisation of silicone rubber textured insulators
Author: Krzma, Adnan
ISNI:       0000 0004 5915 0513
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2016
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Silicone rubber (SiR) outdoor insulators are increasingly being deployed in new AC and DC high voltage transmission systems thanks to their superior performance in wet-polluted conditions compared to traditional porcelain and glass insulators. However, in severely polluted environments, sustained discharge activities and dry band arcing due to surface contamination cause tracking, erosion, and the loss of hydrophobicity on the SiR insulator surface. This degradation can accelerate damage to the insulator surfaces, increasing the probability of a flashover and enduring insulator failure. This thesis presents an experimental study on the electric performance of polluted and aged outdoor SiR polymeric insulators using AC and DC voltages. The research involved an extensive review of the published literature and an investigation of the performance of SiR insulators subjected to different ambient conditions and identifies the modes where most failure and degradation occurred on SiR surfaces. Experimental investigations were carried out to compare the aging performance of two 11kV SiR insulator designs using a rotating wheel dip test under AC and positive DC excitations. A standard polymeric insulator design was used and compared with insulators that had a textured surface. Both insulator designs were fabricated in-house using a vacuum casting machine. Several electrical parameters were measured during the test to characterise the performance of each insulator. Dry band arcing activities were mainly observed on the trunk surface of the conventional profile. A decrease in hydrophobicity was measured on the tested surfaces, and tracking and erosion defects were also observed on both insulator designs. Leakage current measurements showed that drying and discharge activity was greater for a conventional insulator compared with the textured insulator, and more severe degradation appeared under positive DC tests than under AC. These studies showed that insulators with a textured design can improve the performance of SiR insulators against tracking and erosion under AC and positive DC excitations. The electric field and potential distributions along the leakage surface of the 11 kV SiR insulators under dry clean and wet polluted conditions were studied using finite element method COMSOL Multiphysics. The critical of high field regions on SiR surfaces were identified and the power dissipated in the pollution layer along insulator surface was calculated. This study showed useful information about surface heating, which could be used to predict of the formation of dry bands. An investigation of the pollution layer characterisation on conventional and textured pattern designs is described. Several tests were conducted to evaluate the behaviour of the insulator surfaces under different conditions. ESDD and NSDD parameters were measured for different materials, and evaluations for each design were also performed. Leakage conductance measurements on surface designs were determined, and the distribution trends of surface conductance were also characterised. Different rectangular SiR samples were assessed, and an improvement for reducing the pollutant deposition on textured surfaces was observed. In 4-shed insulators, the textured design showed comparable ESDD value with conventional profile. Textured designs also showed slower growth of the leakage current than the conventional design. Clean fog tests (based on a high voltage ramp test) were carried out to investigate the flashover performance of conventional and textured insulator designs. For different ranges of wetting and pollution severity conditions, the textured design showed an improvement in the flashover performance that could reach 16 % compared to the conventional surface. This indicates that the textured surface seems to be more effective under severe ambient conditions. It was also observed that the textured insulator design can improve the electrical performance of SiR insulators under AC and DC voltages.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TK Electrical engineering. Electronics Nuclear engineering