A new approach to interpret the results of return voltage measurements on aged power transformers

Return Voltage Measurement (RVM) is a non-destructive diagnostic test to assess the insulation condition of power transformers. The central time constant and other dominant values together with polarization spectra sensitively reflect the ageing condition of the paper insulation. However, the amount of moisture content in paper insulation has a significant influence on the RVM results, which can lead to confusion in the analysis of the results. The study here shows that it is possible to determine the ageing condition by checking the charging current from short period test cycle in the RVM when the central time constant does not provide a clear indication of the insulation condition. This paper reports this new approach to the interpretation of RVM results, and this can be used to avoid misleading conclusions.