Dielectric Response Measurements

Interest is increasing in replacing the traditional way of determining moisture content in solid insulation of power transformers based on chemical analysis of oil by new methods utilizing dielectric response measurements. Measurement of dielectric dissipation factor or loss tangent at power frequency for any insulation system has been in use for many decades. Two different modeling approaches are frequently used for modeling transformer insulation using polarization–depolarization current (PDC) PDC and or recovery voltage (RV) measurements and their interpretations. For PDC measurement in a substation, certain practical issues need to be addressed. These include the measuring circuit requirements, transformer connections, nature of the excitation voltage, charging and discharging periods, and environmental influences such as rain, temperature variations, and the effects of noise and interference. One of the main criticisms of PDC and RV methods is the long time requirements for their measurements.