Insulation Assessment Based on Dielectric Dissipation Factor Measurement under Non-sinusoidal Excitation

Measurement of the dielectric dissipation factor (DDF) is an important technique for assessing the condition of the insulation in high voltage equipment. Traditionally, pure sinusoidal excitation at the power frequency is used in the testing whereas in reality, the grid voltage is often distorted with harmonics. This paper investigates the impact of harmonics on the DDF measurement. A mathematical expression is developed to quantify the effect of the harmonics on the DDF measured value as compared to the case of non-distorted excitation. It is shown that under the same total RMS magnitude of applied voltage, the DDF decreases with increasing harmonic proportion in the excitation waveform. For validation, laboratory experiments as well as computer simulations were carried out from which the data obtained were obtained and compared with the analytical results.