Effect of Temperature on Frequency Domain Spectroscopy Measurements on Stator Bar Insulation through Triangular Excitation

Frequency Domain Spectroscopy is a promising tool for insulation assessment. In this method, the dissipation factor or $\tan \delta$ of an insulation specimen is measured using primarily sinusoidal excitation across a frequency range. The value of the dissipation factor may depend on the nature of the waveform used as excitation. There has not been much work in the literature on $\tan \delta$ measurement using non-sinusoidal waveforms. In this paper, the FDS characteristics of stator bar insulation used in rotating machines have been evaluated using sinusoidal and triangular excitations and are compared with each other. The measurements were conducted at three distinct temperatures to understand the effect of temperature on the FDS measurements. It was observed that $\tan \delta$ values under triangular excitation are significantly less than those under sinusoidal fields. For both triangular and sinusoidal excitations, $\tan \delta$ characteristics show an increase with temperature. Results suggest that non-sinusoidal waveforms like triangular excitations can also be used for insulation assessment of rotating machines, as the dissipation factor characteristics obtained under such excitations represent the frequency and temperature-dependent polarization processes occurring in the multi-dielectric insulation system very well.