Case Study 2 – Partial Discharge Activity on Switchgear
During a routine partial discharge scan at one of our client’s premises, an abnormality was detected when performing TEV PD measurement on the HT Air-Insulated Switchgear. The issue was promptly highlighted and reported to the client. It was recommended to shutdown Switchgear for checking and rectification works.
A schedule was arranged with the client and I2R’s LEW performed Electrical Switching to shutdown the affected circuits and switchgear. After the Electrical permit-to-work was issued, the HT Air-Insulated Switchgear was opened up for visual inspection and checking. The visual inspection found that there were discolorations and burnt markings on the internal insulating supports of the Switchgear.
Visual Inspection of internal of HT Air-Insulated Switchgear
Based on our professional judgement, it was not safe to put the Switchgear back into service as it could lead to an Electrical flashover. The team quickly discussed possible solutions to restore power to the affected loads.
Firstly, a study on the LT network was done, and a switching plan was done up to transfer the loads to an alternative source. Thus restoring power to the affected loads temporarily.
A new HT Switchgear would require at least 6 months to order and deliver, and there would be high costs involved, which may require time for budget approvals. However, it was not recommended to keep the LT network in the temporary setup for such a long duration. Thus, the team brain-stormed for other options.
The team found that it was possible to by-pass the affected HT Air-Insulated Switchgear panel with a 22kV cable joint. Further study was done to confirm that the Electrical Protection settings for the new setup was adequate. After confirmation of the proposal, the team quickly assembled the required manpower, tools and equipment for the works.
A short length of 22kV cable was to be replaced and certified cable jointers were engaged to carry out the HT cable terminations and jointing works.
HT Cable jointing works
Cable VLF Test was carried out to confirm that the insulation of the HT cable and joints were good.
Cable VLF Test
Completed HT Termination
Completed HT Joint
HT cable Joint encased in concrete for mechanical protection
After completion of the jointing and testing works, the Electrical permit-to-work was cancelled, the circuit was re-energised and the supply to the affected loads was normalised. The HT cable joint was also encased with sandbags and concrete to provide mechanical protection, as well as provide protection of human life against and joint fault.
This case reflects our dedication, professionalism and ability to think out-of-the-box to provide engineering solutions for our clients.
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