Technical Research Of Dielectric Response For High-Voltage Insulation Diagnosis

Dielectric response is a non-destructive insulation diagnosis method, which measures the polarization and depolarization current of the insulation in time domain, and then calculates its low-frequency characteristics to reflect the condition of the insulation system.Because of the limitations of conventional insulation diagnosis methods, this thesis has proposed the dielectric response method and described its measurement methods and research status, and then detailed of the basic theory of the dielectric response and the relationship between time and frequency domain. This thesis has verified the feasibility and validity of the Fourier transform in frequency domain analysis of dielectric response through measuring the time current signal instead of low-frequency measurement. Since the measurement of low-frequency dielectric properties requires a lot of time, and the time domain of measuring the polarization and depolarization current is shorter, so we can transform the measured time domain current signal to frequency domain to obtain low-frequency characteristics of the dielectric through the Fourier transform, in place of directly measuring by the frequency domain method, this can greatly reduce the measurement time and diagnose the insulation condition faster.Finally, experimentally measuring the the polarization and depolarization current of the insulation paperboard under different voltage and polarization time has indicated that more polarization time may get more insulation interior information. Because water is a product of insulation aging, this thesis has discussed the influence of water on the polarization and depolarization current,the result shows the current amplitude becomes larger and the depolarization current curve decays slowly when the paperboard contains water. On this basis, this thesis transforms the depolarization current of dry and moisture absorption paperboard to calculate the low-frequency complex capacitance and dissipation factor, it can be found from the loss factor curve that the moisture makes the dissipation factor value larger and the curve becomes gentle along with the increasing frequency. The experimental results have verified the availability of the dielectric response in this thesis.