A survey of developments in insulation monitoring of power transformers

The aging infrastructure of large GSU and EHV power transformers built in the '60s and '70s poses a serious strategic issue for users worldwide. Catastrophic failures are escalating both in number and cost including environmental impacts. Extension of the useful life of power transformers is the single most important strategy for extending the life of power transmission and distribution infrastructures starting with the GSU at the power plant itself. Continuous assessment of transformer operating condition, accomplished through on-line monitoring, off-line diagnostic tests, and expert system diagnostic and analysis modules, existing and under development, are examples of the practical implementation of that strategy. For example, on-line gas analysis, including oxygen and moisture, offers the potential for gaining a much better understanding and assessment of the dynamic operating condition of such transformers than is possible through periodic laboratory dissolved gas analysis (DGA) tests. However, field experience and learning are vital in order to understand more fully the dynamic relationship between on-line gas analysis and the changing condition of the transformer insulation structure under all operating conditions. This paper presents a survey of new monitoring and diagnostic technologies and applications, including laboratory experimental work, in power transformer insulation monitoring for the purpose of condition assessment.