End-of-life modelling for power transformers in aged power system networks

P. , Jarman and Z., Wang and Q. , Zhong and Ishak, Mohd Taufiq (2009) End-of-life modelling for power transformers in aged power system networks. In: 6th Southern Africa Regional Conference.

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Abstract

Although the design lifetime of transmission transformers was 40 years or less, operational experience has been very good with transformers up to this age, as the majority of transformers on National Grid’s UK system were installed between 1955 and 1975 it is important to understand and predict the future reliability of ageing transformers. This paper presents a statistical analysis of the failure history of the transformer fleet and its age profile in order to understand the trend and whether/how the failure rate is associated with age. Data from failures to date only show random failure modes and no correlation with transformer age. As we know that transformers are subject to ageing mechanisms it is not reasonable to base a prediction of future reliability on this historical data. A further problem arises because with the asset condition assessment techniques available, transformers are being replaced somewhat ahead of actual failure, so a method of predicting the ‘age of failure’ of the replaced transformers has had to be developed using DP analysis. For in-service transformers a calculation of life based on the physical ageing process of paper insulation using design data, loading condition and ambient temperature, under the normal IEC assumptions, has been made. This analysis shows that for a typical network transformer, the ageing rate depends more on transformer design and cooler operation temperature settings than on loading. If the cooler on temperature setting is low and the transformer thermal behaviour is as designed, then the expected lifetime would be in excess of 100 years. Despite this there have been examples of age related failures indicating that operating temperatures for at least some transformers are significantly higher than designed. Further statistical and thermal modelling is required to fully understand how the range of thermal parameters of transformers will affect the ageing rate of the transformers, their future reliability and hence the replacement plans required to maintain the future reliability of the power system.

Item Type:Conference or Workshop Item (Paper)
Uncontrolled Keywords:transformer end-of-life, statistical analysis, transformer thermal model, DP value, power system reliability
Subjects:T Technology > TK Electrical engineering. Electronics Nuclear engineering > TK3001-3521 Distribution or transmission of electric power
Divisions:Faculty of Electrical and Electronic Engineering > Department of Electrical Power Engineerings
ID Code:1712
Deposited By:Norfauzan Md Sarwin
Deposited On:05 Aug 2011 10:44
Last Modified:05 Aug 2011 10:44

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