Study of recovery voltage mechanism [transformer insulation diagnosis]

Three methods have been used to study the mechanism of the polarization process in oil immersed single-phase transformer insulation, in which the LV winding is grounded to a grounded metallic oil container. In the first method, a dc high voltage of 200 V is applied to the HV winding. The resulting current is measured for a time duration of 1000 seconds. In the second method, the recovered voltage after polarization is measured using the developed system. In the third method, the ac impedance behaviour of the transformer insulation between the HV and LV windings is studied. All the three measurements are automated using the Labview software package and GPIB controlled instruments. After collecting the data, Matlab is used for simulation. A close relationship is established with the three methods in the form of an equivalent circuit with 8 polarization branches of various time constants.