Dielectric Dissipation Factor Measurement of Power Equipment under Distorted Excitation Voltage

The dielectric dissipation factor (DDF) is a useful parameter for the diagnosis of high voltage equipment insulation condition. Traditionally, the AC power grid voltage was considered pure sinusoidal. Due to the increasing presence of non-linear loads in the power system, the grid voltage nowadays gets distorted with high frequency harmonics. This paper investigates the impact of distorted voltage on the DDF measurement. Based on a circuit model with the polarization loss, a mathematical formula is derived which shows that, given the same RMS applied voltage, the DDF value will decrease with increasing harmonic distortion level. The theoretical formulation is implemented in computer simulation using MATLAB Simulink to validate the results. Laboratory experiments were carried out on a 33kV dry-type current transformer which confirmed the monotonically decreasing pattern, but the trend is more complex.