00_ageing_oil - Degradation of cellulosic insulation in...

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Degradation of cellulosic insulation in power transformers. Part 3: Effects of oxygen and water on ageing in oil A.M.Emsley,X.Xiao, R.J.Heywood and M.AIi Abstract: Heat, water and oxygen accclcrate the degradation 01' cellulose insulation in eleclrical tl.ansrormers. Their effects on insulation have bccn studied over a number of years using degrcc or polymcrisation (DP) of tlie paper as a iiicasurc of agcing. Results arc reported of a systemic study to nieastirc the relative cl'fcctivemss of Cach component individually and in combination, on ageing in oil in a three-piiramcter, two-lcvcl, partial factorial experiment. Ageing was measured in terms of change of degree of polymerisation of the paper and analyscd according to recently developed models. In addition, Lhc concenlrations of furlhral-hised degradation products in tlie oil wcrc incastired Water and Lcmpertiturc arc most effective in accelelating ageing, with oxygen about one-third as elficicnt. There is a strong synergistic effcct between tenipcrature and water, a weaker synergism between temperature and oxygen, but, importantly, a11 apparent anlagonistic effect bctwccn water and oxygcn, at low water levels. IT correct, the aiitagonisni implies hiit the effectiveness of watcr, as an acmlcrator of ageing, decreases with incrcasing levels oroxygeii in the oil at low watcr levels, which could explain why the insulation in scrapped transformers is sometimes found to be iii very good condition. 1 Introduction A high-voltage power tl.ansfornier. is cxpected to operate reliably for up to 40 years. The onset of dccrcasing reliabil- ity is associated with a variety ofcauscs, many of which are design specific. However, the underlying, life-limiting Tal- Lure of all designs is related to the thermal degriidiition oi paper insulation on the windings [I, 21. The paper contains about 90% oT ccllulose, 67'X of lienii-cellulose and 34% of lignin, and it deteriolalcs slowly the constituent largc niolecukir chains break down during service. The process is accelerated by heat, moisture and oxygen, which arc all present in an operating transformer. a previous paper [3], studies have been reporled the [ormation oT rurfiiral products during the ageing of dried Kraft and cotton insulation paper in dry iiisulating oil under acceleralcd laboratory conditions. It was dernon- strated that 2-furaldehyde was the mas1 significant product or ageing detcctable in the oil and that the concentra- tions of all fllran-rebated products inilially iiicreascd to a low plateau concentration in the oil. As ageing proceeded and the DP of the paper dropped below about 400, the con~ntration of ageing products in the oil began to rise 0 WE, 20(X) IEE Pmw~v/ings oiiliiic 110. 20000021 DM IO. 1C49/ip~sml:2tMooo2 I 1':ipcs ilreival 14111 Scptcnclnkr I999 A.M. Emslcy is will? thc School of Pliysia ;and Chcmislty, Univcrsily of Surccy, Guildford. Sunzy, CU2 5x11, UK exponcnlially to a inaxiiiiuin valuc and then decrcascd, when the paper was fully degraded. It was therefore pro- posed that fiirfural analysis or oil WAS
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This note was uploaded on 06/08/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.

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00_ageing_oil - Degradation of cellulosic insulation in...

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