Accelerating Dielectric Response Measurements on Power Transformers—Part II: A Regression Approach

Dielectric frequency response, also known as frequency-domain spectroscopy (FDS), was introduced about a decade ago as the preferred method to estimate the moisture content in the cellulose insulation of power transformers. A conventional FDS measurement is carried out as a frequency sweep down till 100 μHz, thus causing unavoidable large measuring time due to the very low frequency oscillations. Nevertheless, FDS is the favored choice for onsite measurements due to its robustness against noise. This contribution proposes a newly developed modification to the FDS measurement technique. In Part II, of a two-part series, we propose reducing the measuring time by measuring only a fraction of a complete oscillation. Regression techniques are then used to calculate the amplitude and phase shift of the fraction. The capacitance and dissipation factor (tanδ) are then calculated for each individual oscillation. The proposed advancement described in this part could reduce the measuring time by up to 90% compared to a conventional FDS.