Frequency domain measurement as quality and diagnostic tool for power transformers

In recent years, attention has been focused on measurement of various dielectric properties in frequency domain to assess the condition in each of the dielectric media, especially in paper oil insulation systems, employed in Power Transformers. This paper details some of the findings of the laboratory investigations as well as measurements carried out on in-service Power transformers by monitoring dielectric properties in frequency domain. Interpretation has been focused on characterizing the variations in the spectral response of dielectric parameters like Dielectric loss, Capacitance and Permittivity as a function of frequency to estimate moisture content and for condition assessment of the composite insulation system of the transformer and thus to arrive at the degree of degradation of each of the insulation system.