Bulk Oil Circuit Breaker Bushing In Situ Refurbishment

Completed

Other Power and Storage Technologies(Electricity transmission and distribution)

Applied Research and Development

ENGINEERING AND TECHNOLOGY (Electrical and Electronic Engineering)

Not Cross-cutting

Project Contact
National Grid Electricity Transmission

Network Innovation Allowance

Ofgem

01 December 2013

01 November 2016

35 months

£238,799

Power

London

Network Innovation Allowance

Project Contact, National Grid Electricity Transmission

To establish an alternative and cost effective refurbishment that creates life extension and remove the requirement to undertake any asset replacement. This will enable BOCBs to continue in service beyond their original design life. A trialled procedure for in-situ bushing replacement. A methodology for in-situ bushing refurbishment. A business implementation procedure.

In a power system, circuit breakers are used to clear faults when they occur. There are various different types of circuit breakers used by utilities to do this, depending on the requirements of the location. Common types of circuit breakers include Gas Insulated Switchgear (GIS), Air insulated Switchgear (AIS) and Oil Insulated switchgear, which this project focuses on. The Bulk Oil Circuit Breaker (BOCB) itself is statistically the most reliable circuit breaker on the National Grid system, bushing issues aside. Each of the BOCBs on the National Grid system has 6 bushings used within that system, where the bushing is used to electrically insulate the working parts of the circuit breaker and the transmission system from the earthed housing in which it is contained. Each bushing refurbishment cost is almost half the price of a modern AIS complete circuit breaker (uninstalled). With aging assets, 3 historic disruptive failures since 2000 and up to 10 replacements per year (an average of 6 bushing refurbishment per year since 2009) at £45k per bushing (excluding site works), consideration has to be given to best value and for retaining BOCBs in the system. With over 100 BOCB over 50 years of age by the end of RIIO-T1 (2021), the current business plan has these assets planned for replacement. If the bushings can be refurbished in situ then the cost of BOCB refurbishment may be significantly reduced. National Grid do not have the capability to deliver this service internally, hence the need to develop this capability with a supplier. Development The method proposed is to analyse the moisture content within the bushing using standard techniques. Then, National Grid will remove the bushings, and send them to NAREC who will perform laboratory testing and strip down the bushing to assess the physical condition. This will provide more evidence on the relationship between moisture content and condition to trial the redesign proposals to minimise any further moisture ingress. When this piece of work has been completed, we will attempt an in-situ refurbishment of the bushings on the BOCB. This will enable us to keep the electrical insulation up to the standard required in IEC 60422 and will address the life limiting component that limits any life extension opportunities.Note : Project Documents may be available via the ENA Smarter Networks Portal using the Website link above

10/07/18