Characterisation of textured insulators for overhead lines and substations

Charalampidis, Panagiotis 2012. Characterisation of textured insulators for overhead lines and substations. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Pollution flashover constitutes the predominant parameter for the design,specification and dimensioning of high voltage outdoor insulation [1-2]. For over a quarter of a century, polymeric insulators have been used for overhead lines and substations due to their enhanced performance in highly polluted environments. This is mainly attributed to the hydrophobic properties of polymeric surfaces thatlead to a reduction of surface wetting and, thus, to a reduction of leakage current and discharge activity that could result to a flashover. However, under severe ambient conditions, discharge activity is not totally eliminated. The present investigations have demonstrated the development of dry bands and partial arcs on polymeric insulators (Chapter 3). While ‘cap and pin’ ceramic insulators - e.g. porcelain and glass - employ special anti-fog designs of increased leakage path introduced by the presence of deeper ribs, such profiles cannot be used for polymeric insulators due to moulding restrictions [1-1]. Yet, these moulding properties allow the fine texturing of the polymeric surface [1-7]. Textured insulators are a novel approach for the improvement of polymeric insulators using a surface design consisting of an array of hemispherical protuberances of various configurations and range of diameters. The objective is to reduce power dissipation (P = EJ) on the insulator surface by reducing the electric field gradient E and current density J (Chapter 2). Moreover, an increase of the longitudinal creepage path can be achieved without the need of increasing the overall length of the insulator. Where discharges do occur, the formation of parallel current paths could lead to less harmful discharges hence mitigating damage due to thermal stresses. An initial theoretical classification of the textured designs resulted to a shortlist of textured patterns that could be employed for the development of a full insulator prototype. At the next stage, these patterns were experimentally evaluated in a series of material tests in accordance to IEC-60587 inclined-plane test procedure [Chapter 5]. Rectangular silicone rubber samples with a plane surface were tested along with samples with a textured finish to assess the performance against erosion and tracking. The improvement introduced by these textured patterns in comparison with conventional non-textured samples was outstanding [2-48, 49]. The intersecting square pattern showed the best performance, hence it was chosen for the development of a full textured insulator. Conventional 11 kV silicone rubber insulators and textured insulators with the same shed profile were cast in-house using vacuum injection casting techniques. There are no international standards for the artificial testing of polymeric insulators. In this work, a proposed test procedure for non-ceramic insulators is described (Chapter 3). Clean-fog tests of conventional (Chapter 4) and textured insulators (Chapter 6), for a range of wetting and pollution severity conditions,showed that textured insulators showed an improved flashover performance that in some cases reached 26 %. Surface texturing seems to be more effective under severe conditions of wetting and pollution and when hydrophobicity is reduced, like the temporary loss of hydrophobicity observed for silicone rubber insulators in service.

Item Type:	Thesis (PhD)
Status:	Unpublished
Schools:	Engineering
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Uncontrolled Keywords:	Textured, Insulators, Pollution, Flashover, Polymeric
Funders:	EPSRC
Date of First Compliant Deposit:	30 March 2016
Last Modified:	09 Jan 2018 23:13
URI:	https://orca.cardiff.ac.uk/id/eprint/43818

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