Challenging Composite Insulator Design Rules (Champions)

Completed

Other Power and Storage Technologies(Electricity transmission and distribution)

Applied Research and Development

ENGINEERING AND TECHNOLOGY (Electrical and Electronic Engineering)

Not Cross-cutting
Sociological economical and environmental impact of energy (Policy and regulation)

Project Contact
National Grid Electricity Transmission

Network Innovation Allowance

Ofgem

01 January 2020

01 April 2021

ENA months

£200,000

Power

London

Network Innovation Allowance

Project Contact, National Grid Electricity Transmission

This project will review the design parameters used for designing the insulation systems when composite insulators are used in OHLs. This review will be supported by COMSOL simulations of the insulation systems and laboratory testing of short sections of insulators. The designs calculations, simulations and testing will all be used to challenge the existing design rules used for composite insulators. This project will focus on challenging the design rules across three work packages:1. Characterisation and optimisation of the Composite Insulator Interface sealing Many manufacturers use novel internal sealing mechanisms to prevent moisture ingress at the ends of composite insulators; where the metal end fittings are connected to the insulation. However, due to its simplicity and low cost, many are now using over moulding of the end fittings during the injection moulding process. Others can rely on proprietary RTV sealants applied after the compression of the end fittings. Whilst this may not be so problematic for medium voltage insulators with low electric fields and discharge, it is considered undesirable for higher voltage insulators, such as those destined for transmission voltages.Whilst composite insulators at extra high voltage are relatively new to the UK, elsewhere the technology is quite commonplace. During this projected, it is proposed to conduct a comparison of various sealing technologies in order to inform our technical specifications and whole life value.2. Controlled electric field distributions for composite insulators The current practice enables replacement of conventional ceramic strings with composite insulators while using standard arcing horns. The current NG standard enables attachment of grading rings to insulators or to the metal fittings used to connect the insulator. From an insulator perspective, the accurate positioning of the grading ring is critical for electric field magnitudes and their distribution around the end fittings and along the insulator profile. Therefore, controlling such field parameters allows to improve the long-term performance of the insulator.The design of arc protection is based on the historic designs of ceramic insulator strings, and these may not be the most optimum solution for composite insulators during fault/transient events. It is, therefore, proposed to study the effects of arcing horns and grading rings on the field distribution around polymeric insulator surfaces.3. Challenging the length requirements for composite insulatorsInsulator creepage distances are presently determined by historic practice applied to ceramic insulators (Porcelain & Toughened Glass). This has an impact on string length given the necessary geometry and size of traditional cap & pin insulators. The Basic Insulation Level (BIL) of the overhead line is managed via the application of known arc gaps to insulator strings which provides recoverable insulation in the event of transient overvoltages.Given the variable parameters of composite insulators and indeed the improved hydrophobicity, there is an argument to suggest that the length of the insulators could be reduced to provide the equivalent BIL and maintain the existing creepage distances. Given the nature and hydrophobicity of composite insulators, there is an opportunity to challenge the existing creepage distances requirements.The project will investigate insulator dimensioning based on theory and knowledge of the discharge thresholds (for axial length and surge overvoltage levels) and pollution performance to determine the specific creepage and the total creepage length of polymeric insulators. The gains and benefits of such investigations will be highlighted against existing practice based on National and international standard practices for insulator dimensioning. The objectives of this project are to:1. Understand the impact of different molding techniques on the life of composite insulators in greater detail.2. Identify if there are more suitable design rules for the electric field distribution along a composite insulator3. Identify if the creepage requirements for composite insulators can be modified for different designs.

This project will investgate three key areas for the design of OHL insualtion systems and challenge the exsiting designs rules, based on recent advances in composite insulation technologies.

02/11/22