Diagnosis of transformer insulation condition using recovery voltage measurements

Moisture is one of the factors that cause transformer insulation degradation. The detection of moisture in oil and paper insulation is crucial in determining the health of transformer insulation system. High moisture content severely degrades the insulating strength of oil and paper and may eventually cause failure. In recent years, new diagnostic and monitoring techniques have been promoted to complement the classical insulation resistance, power dissipation factor and polarization index measurements. The new test method described in this paper is based on analysis of the polarization spectrum traced from the results of Recovery Voltage Measurements (RVM). This method makes possible assessment of the condition of oil/paper insulation system. This paper shows some applications of RVM for determining the moisture level in the power transformers. The possible use of this method as a diagnostic tool for evaluates ageing trends or actual state of insulation is also discussed.