The Influence of Moisture Content in Oil-Paper Insulation System on Parameters of Return Voltage Measurement

As a non-destructive insulation diagnostic technique, the polarization spectrum method based on return voltage measurement has been employed to assess the state of insulation of the transformer. But how does the moisture content affect the parameters of RVM is not clear. In this paper, the effect of moisture content on the parameters of return voltage is studied based on experiments. The result shows that maximum value of return voltage (Urmax) and initial slope (Si) increase with the increase of moisture content in second-order function, while the central time constant (tcdom) decreases with the increase of moisture content in second-order function. The central time constant varies strongly with the change of moisture constant, so it is considered as a reliable indicator to evaluate the moisture level in oil-paper insulation system of transformer.