Research on return voltage method to diagnose insulation moisture in transformer

Moisture in power transformer strongly influences the dielectric properties of oil-paper insulation system. The insulation paper gradually degrades over time, therefore, it is imperative to assess integral condition of oil-paper insulation for assuring a normal operation of power transformers. As a non-destructive diagnostic technique, return voltage measurement is an effective assessment method of water content in transformer pressboard. The study presented in this paper aims of further investigating the reliability of the quantification of water content using dominant time constant in transformer pressboard. Field tests performed on several transformers in different status have shown that the return voltage measurement method can estimate the moisture content in paper insulation of power transformers effectively.