Combustible Gases in Redundant Oil Filled Cables

Completed

Other Power and Storage Technologies(Electricity transmission and distribution)

Applied Research and Development

PHYSICAL SCIENCES AND MATHEMATICS (Chemistry)
PHYSICAL SCIENCES AND MATHEMATICS (Metallurgy and Materials)
ENGINEERING AND TECHNOLOGY (Electrical and Electronic Engineering)

Not Cross-cutting

Project Contact
National Grid Electricity Transmission

Network Innovation Allowance

Ofgem

01 December 2013

01 June 2014

6 months

£110,000

Power

London

Network Innovation Allowance

Project Contact, National Grid Electricity Transmission

The objectives are: To identify the root cause of the gas To identify an appropriate mitigation method To provide a business implementation methodology This project will be successful if we: Identify the root cause of the gas Identify a potential mitigation method Provide a business implementation methodology

National Grid decommissions cable systems in line with the National Grid current cable decommissioning policy. This policy document defines the requirements and specifies considerations that should be made when assessing options for oil filled cable systems that have reached end of life. For each individual case, a thorough survey and risk assessment is carried out identifying the best solution. Until recently almost all cables that have been decommissioned and left in situ are flushed with a water based solution to remove as much of the oil from the cable as reasonably practicable. A contract was awarded to a specialist cable contractor to decommission a 400kV circuit which ran parallel with an already decommissioned circuit existing circuit. As part of the scope of works earthing of the already decommissioned circuit was required to comply with the NSI 5 regulations. In preparation for plumbing the earth braids onto the mechanical caps on the ends of the cables, the Jointer was in the process of venting the cable, this is common practice when plumbing on oil filled cable. After the cable had been venting for about half an hour the jointer commenced plumbing operation the Unaware and never having experienced this phenomenon he lit his gas torch to start his plumbing process. The gas torch he was using ignited gases coming out of the cable causing a long yellow coloured flame about 1 metre in length to come from the cable. Fortunately no one was injured. We are unaware of either the gas that has caused this effect, or the underlying mechanism that has caused the build-up of the gas in the cable. This work is to undertake analysis of the cable to ensure future work does not experience the same problem. Research Following this incident, an initial investigation has already taken place to identify the root cause. Unfortunately the results have been inconclusive as there is not enough understanding of the chemical processes taking place within the cable to cause a gas to generate. Numerous samples of the gases have been taken but we are unable to understand how these were generated. The work we are going to undertake involves taking samples from the cable affected, and then completing forensic analysis on the samples in a laboratory. When the analysis is complete, we will look to replicate the mechanism in a controlled environment, and then identify mitigation methods for this effect.Note : Project Documents may be available via the ENA Smarter Networks Portal using the Website link above

10/07/18