This thesis deals with the measurement and analysis of partial discharge(PD) for insulation diagnosis of cast-resin transformers. A PD measurement system which consists of a capacitive probe, a coupling network and an amplifier is set up to detect PD pulse.
The capacitive probe is proposed to detect PD pulses without connecting a high voltage conductor. The coupling network is designed to attenuate 60[Hz] by 130[dB], and its low cutoff frequency of -3[dB] is 100[kHz]. The amplifier with the gain of 40[dB] is fabricated, and its frequency bandwidth is in ranges of 500[Hz]∼45[MHz]. Sensitivity of the PD measurement system is 0.35[㎷/pC] for positive and 0.45[㎷/pC] for negative polarity, respectively.
A planar-planar and a planar-point(10[㎛]) electrode are fabricated to simulate insulation defects in cast-resin transformers. In the experiment, the rise-time of PD pulses is about 11[㎱] in the defects, and the phase distribution of PD pulses is in ranges of 8[°]∼90[°] and 192[°]∼277[°] in the planar-planar electrode, and of 345[°]∼128[°] and 165[°]∼295[°] in the planar-point(10[㎛]) electrode.
The results showed that the proposed PD measurement system can detect PD pulses and analyze their electrical characteristics such as the magnitude and the phase distribution of PD pulses.