| 要約: | Manufacturing or assembly defects in gas-insulated equipment can introduce field enhancements that could lead to partial discharge (PD). This paper examines the PD characteristics of SF<sub>6</sub> alternatives considered for potential application to retro-filling existing SF<sub>6</sub>-designed equipment. The PD performance of the C<sub>3</sub>F<sub>7</sub>CN/CO<sub>2</sub> gas mixture and SF<sub>6</sub> were characterised adopting the ultra-high frequency (UHF) method and investigated for different defect configurations, pressures, and gas mediums. Hemispherical rod-plane and plane-to-plane configurations with needle on the high-voltage (HV) and ground electrodes were used to mimic conductor and enclosure protrusion defects, respectively. The results demonstrate that with a needle length of 15 mm, the 20% C<sub>3</sub>F<sub>7</sub>CN/80% CO<sub>2</sub> gas mixture had almost half the partial discharge inception and extinction voltages (PDIV/EV) of SF<sub>6</sub>. For less divergent fields, the 20% C<sub>3</sub>F<sub>7</sub>CN/80% CO<sub>2</sub> gas mixture demonstrated a comparable PDIV/EV performance as SF<sub>6</sub>. The phase-resolved PD patterns of the 20% C<sub>3</sub>F<sub>7</sub>CN/80% CO<sub>2</sub> gas mixture demonstrated a 3-stage transition phase that was not observed with SF<sub>6</sub>, which could be due to the discharge mechanism of the weakly attaching CO<sub>2</sub> gas used within the mixture.
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