Estimation of Transformer Insulation Paper Moisture Content Using Polarization and Depolarization Currents Measurement

Moisture in oil-paper insulation system is one of the destructive factors which may cause power transformer failure. Decrease of dielectric strength, breakdown voltage and increase of partial discharges rate are some of the effects of moisture increment in the insulation system. Also, it is known that cellulose insulation decomposes in the presence of moisture and can decrease transformer’s lifetime. In the present study, the use of PDC method for estimating paper moisture content of an experimental insulation model have been investigated in three different temperatures. With every temperature increment step, moisture slowly migrates from paper to oil until the equilibrium condition be achieved. PDC tests were done at every temperature step. It can be seen from the results that value of the tail of polarization current, which is dominated by paper conductivity, decreases with moisture migration from paper to oil in a constant temperature. Thus, an effective method for estimating paper moisture by calculating paper electrical resistance from PDC measurements is presented. Test results demonstrate that paper moisture content can effectively be estimated from paper resistance when the effect of temperature has been eliminated and all of the results have been compared in a same temperature. NI LabVIEW 2013 was used to control the measurements procedure and to save measurements data. Further calculations were done using MATLAB 2016.