Learnings

Outcomes

The outcomes from WS1 may be summarised as follows:

• No dielectric change / gas composition change as a result of the leak repair

The gas analysis results after the leak repair do not suggest that the detected levels of nitrogen (N2) were higher than the ones that were detected during the preliminary tests. Moreover, the outcomes of the high voltage performance testing do not indicate the presence of conductive particles within the test sample volume following the casting process. The results suggest that there were no conductive particles deposited on the surface of the electrodes used within the high voltage test vessel. The results also suggested that the insulating performance of the gaseous insulating medium was not affected following the casting process. The variation found in the breakdown U50% among the different test cases was less than 3%, which can potentially be attributed to the statistical variations of the test results. 

• No significant gas ingress into the pipes as a result of the leak repair

The gas analysis after the high voltage testing did not indicate any N2 contamination, above the expected levels in the interconnected volumes of the test rig and the stainless-steel vessel.

• Conductivity of the joint improved after the repair

The obtained resistivity measurements indicate that the resulting encasement provides a more effective equipotential bond across the joint which results in an improved conductivity following the repair.

Lessons Learnt

As part of WS1 a testing regime was established to evaluate the performance of metal alloy leak seals.  The dielectric change testing will be conducted again at the end of WS2.

In WS3, a number of lessons were identified:

• mechanical properties of potential leak sealing materials should also be considered as well as the gas barrier performance.
• When modifying a test rig for evaluating leak sealing performance, the potential for the rig to leak (not just in the test part) should not be overlooked

Dissemination

A presentation on the metal alloy leak sealing technology was given to other utilities attending the Eurodoble conference in Rome in October 2022.  A similar presentation is planned for transmission utilities at the ITOMS conference in Belgium in April 2023.

On completion of WS1, a press release was made by National Grid to promote the work which had already started to be used within the business.  https://www.nationalgrid.com/novel-anti-leak-tech-helps-keep-national-grid-substations-service-during-sf6-repairs.  This was picked up and reported by, among others, Energy Live News, Utility Week, Industrial News, Current News websites.

A test object used in WS1 was on view at the Energy Innovation Summit in Glasgow in September 2022.