Measuring the Dissipation Factor of Capacitive Equipment Under Damped AC Voltage

Damped ac (DAC) test is widely used in the insulation diagnosis of capacitive power equipment due to its flexibility and multifunctionality. The dissipation factor (DF) is one of the crucial functions in the DAC test system. However, the resolution of the existing DF measuring method under DAC is too low (i.e.,
$1\times 10^{-3}$
) to accurately measure the DF value of some power equipment, such as power cables. Accordingly, this article proposes an improved DF estimation method based on the combined analysis of voltage and current waveforms of the DAC stress. Two improvements are involved in the developed method: one is that DAC voltage and current are measured simultaneously and a measurement approach is developed to minimize theoretical phase errors and avoid any increase in the ground voltage owing to the breakdown of the test object; the other one is that a DF value estimation algorithm via the joint application of all-phase fast Fourier transform and a nonlinear least squares approach is developed, and its superior accuracy and robustness are verified through simulation. Finally, the strength and feasibility of the proposed method are validated via a laboratory experiment on a 10-kV variable DF standard capacitor, along with a comparison with the conventional solution. The result shows that the proposed method can accurately measure DF with an order of
$1\times 10^{-4}$
.