Using of parameters of RVM measurement for qualitative appreciation of power transformers insulation state

The measurements of dielectric properties of high voltage equipment insulation in service conditions have seen a new renaissance during the past decade. The specific method of recovery voltage measurement called RVM is one from the commercially widely spread. The method is well known but the interpretation of test results is still subject of evolution and discussion. This paper contributes to this topic by a discussion on sensitivity of RVM parameters (main time constant and initial slope of recovery voltage) to moisture content and ageing degree of paper-oil insulation of power transformers. Test results from RVM measurements on 60 power transformers in service are presented in this paper. This data is compared with measurements of degree of polymerisation of paper samples, with service age of power transformers and with measurements of water content or in fact measurements of change in water content during drying.