Jun 2018
Electricity Transmission
Electrical Characterisation of Silicone Oil (ECOSO)
Jun 2018
Dec 2020
National Grid Electricity Transmission
Oliver Cwikowski -box.eto.innovationteam@nationalgrid.com
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Network Innovation Allowance
ET - New technologies and commercial evolution, ET - Safety and health and environment
Asset Management and Condition Monitoring
National Grid Electricity Transmission (NGET) currently has a population of several thousand Sealing Ends (SEs) of all types (including fluid filled and XLPE) across Great Britain. With the expected increase in undergrounding technologies and the difficulties with new OHL routes, NG’s SE population is expected to increase.

Experience has shown that since rapid uptake of XLPE cables in the early 2000s, that the Cable Sealing Ends (CSEs) used to terminate the cables have suffered several bulk replacements due to performance issues; for different reasons. Which has required NG to manage the increased risk presented by these assets during their early replacement, and has ultimately led to a rapid replacement timeline.  With the advent of Condition Monitoring Surveys (CMS), there is opportunity to identify the poor condition assets and manage their risk effectively, without the need for immediate replacement.
However, there is a lack of understanding on the degradation mechanisms for silicone oil filled CSEs, in particular the interaction between oil contamination/degradation and discharge/breakdown process for silicone oils used in these CSEs. This poses challenges to conducting effective assessment of the condition of the CSEs in order to inform the management of CSEs, their replacement strategy and manage their end-of-life.
The objectives of the project include:

1, To understand the effect of contamination and degradation on discharge/breakdown degradation process in silicone oil/solid insulation system of the CSEs.
2, To propose the useful diagnostic parameters which can contribute to the insulation condition assessment of the CSEs.
The replacement of 153 sets of cable sealing ends is presently being considered at an estimated cost of over £10m. This project will help inform the development of a new specification for silicone oils and improve our ability to manage ones that have shown signs of damage. This could prevent the replacement of CSEs in the future and reduce the risk associated with these assets.