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Projects: Projects for Investigator
Reference Number NIA_NGET0044
Title Transformer Oil Passivation and Impact of Corrosive Sulphur (TOPICS)
Status Completed
Energy Categories Other Power and Storage Technologies(Electricity transmission and distribution) 100%;
Research Types Applied Research and Development 100%
Science and Technology Fields PHYSICAL SCIENCES AND MATHEMATICS (Chemistry) 50%;
PHYSICAL SCIENCES AND MATHEMATICS (Metallurgy and Materials) 50%;
UKERC Cross Cutting Characterisation Not Cross-cutting 100%
Principal Investigator Project Contact
No email address given
National Grid Electricity Transmission
Award Type Network Innovation Allowance
Funding Source Ofgem
Start Date 01 October 2011
End Date 01 February 2015
Duration 40 months
Total Grant Value £366,000
Industrial Sectors Power
Region London
Programme Network Innovation Allowance
Investigators Principal Investigator Project Contact , National Grid Electricity Transmission (100.000%)
Web Site http://www.smarternetworks.org/project/NIA_NGET0044
Objectives The objective of this proposal is to reduce the risk of transformer failure and unreliability resulting from corrosive sulphur in oil. This key objective will be met by: Better understanding of the mechanism by which copper sulphide failures occur and the effectiveness of passivation Fully understanding the effects, both chemical and electrical, of passivation on transformer insulation performance Investigating the reasons for silver corrosion in tap changers and to formulate monitoring/assessment strategies in order to provide a measure of asset health. This project will be successful if we understand and have an increased learning around the transformer oil passivation issue, specifically around silver corrosion on tapchangers.
Abstract Formation of corrosive sulphur in oil and subsequent copper sulphide deposition in paper has led to a number of large transformer failures worldwide, it was the cause of the failure of Lackenby SGT4 and other transformers will be removed from the system early because the problem is believed to be advanced. Part of the complex process leading to transformer failure involves the mobilisation of copper containing material into the paper insulation surrounding the windings, which is known to be influenced by the presence of corrosive sulphur species in the oil, and extreme operating conditions. Although there have been many attempts to better understand the mechanism by which formation of copper sulphide occurs none have yet been conclusive, they have not led to sufficient understanding to allow diagnosis of the problem without inspection and better mitigation methods may still arise if the mechanism is better understood. Laboratory studies of the mechanism have largely focussed on the thermal aspects of the mechanism and also the interactions between oil, paper and the surface of copper conductors. This study will use facilities in the Tony Davies High Voltage Laboratory at the University of Southampton to evaluate corrosive sulphur formation in covered conductor samples that are carrying current and will attempt to recreate more accurately the conditions in a transformer in order to better replicate the mode of failure witnessed in transformers i.e. turn to turn failure. The mechanism by which copper sulphide migrates through the paper and the possible interaction of mobile copper ions and/or complexes in the oil will also be investigated. One mitigation strategy employed by transformer owners, including National Grid through OESB 9/08, is to protect the copper surface of the windings by the addition of chemical passivators, such as Irgamet 39TM, to the oil. Passivators are designed to interact with the copper surface to provide a protective barrier and reduce corrosion. 1Irgamet 39 TM is itself a reactive species designed to be soluble in transformer oil, which liberates a benzotriazole derivative (the active passivator molecule) at the copper surface. There are two by-products from this process, namely formaldehyde and an amine, both of which may have an impact on the properties of the oil. The effect of these compounds may not emerge until additional amounts of passivator have been added. The effects of these compounds may also be studied using the vial tests. Samples of paper-wrapped windings from failed transformers (provided by National Grid) will also undergo passivation tests, to assess how effective passivation is on "at risk" plant. In parallel with developing understanding of the chemistry involved in the addition of passivators to transformer oil, studies will be undertaken to determine its effect on the thermal/mechanical/electrical properties of the paper/oil insulation system over time. In particular it is necessary to establish whether the addition of passivation effect interturn losses or cause increased operating temperatures. The work on passivation will involve close collaboration between two PhD students, one based within Chemistry and the other in the Tony Davies Laboratory. Oil reclamation of transformer oil through heated clay columns has been used as a remedial measure when corrosive oil is detected and was successfully demonstrated as an effective technique in a previous IFI project. However,through that study and following regeneration of oxidised oil in recent years there has been undesirable corrosion in silver tap changers (OESB 4/09 refers). There is also some evidence of increased gassing in some transformers using reclaimed oil. It is suspected that the reclamation process is itself adversely affecting the oil, and possibly even introduces corrosive substances such as elemental sulphur. The method that has been proposed for this project that will solve / investigate the problem includes; Initial review of current understanding of the impact of passivation on power transformers Interim report on silver corrosion of tapchangers Report on initial studies into effects of passivation Recommendations to minimise silver corrosion in tap changer units Interim report on the chemistry of passivation and its effects on thermal and electrical properties Interim recommendations on use and application of passivators Interim report on the development of condition assessment techniques Final Recommendations and ReportNote : Project Documents may be available via the ENA Smarter Networks Portal using the Website link above
Publications (none)
Final Report (none)
Added to Database 17/12/18