Reducing frequency domain spectroscopy measurement time for condition monitoring of transformer oil‐paper insulation using non‐sinusoidal excitations

Abstract

In conventional frequency domain spectroscopy (FDS) measurement, sinusoidal excitation is applied to a composite oil-paper insulation under test, for a minimum of two cycles over a wide range of frequencies typically starting from 1 kHz to 1 mHz or even upto 0.1 mHz. The frequency sweep down to 1 mHz, is inevitably time consuming especially in lower frequency ranges. Considering the aforesaid fact, the main aim of the present study is to reduce overall FDS measurement time. The insulation under test is subjected to some fraction of one full cycle of excitation, and the corresponding dielectric response current is measured for each fraction. Using least square curve-fitting technique, response current over two cycles is predicted from which dielectric dissipation factor (tanδ) is calculated. For this contribution, sinusoidal and non-sinusoidal excitations in form of triangular waveform with five different initial slopes are used as excitation voltage. The technique is experimentally validated on three samples with different preset moisture contents prepared in the laboratory. The dielectric dissipation factor obtained by using the proposed technique is compared with the conventional method using two cycles, which show negligible differences. Most important of all is the overall test time, which can be brought down significantly when compared with conventional FDS measurement.