The possibilities and limits of estimation of ageing degree of paper-oil insulation in power transformers by recovery voltage method

Thanks to economical conditions in power systems in the last few years, the life management and estimation of the remaining service life of power transformers has got more and more attention. We have to know what is the present state of paper-oil insulation beside knowledge of transformer history and operating conditions (temperature, loading). One methods of judgement of insulation state is recovery voltage method. We used this method successfully for verification of effectiveness of the drying process in the past and for verification of quality of revision and repair work. In this paper we try to show the possibilities and limits of this method in estimating ageing degree of power transformer insulation in service conditions by comparing the results of RV measurements with the results of degree of polymerisation of the paper sample.