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The levitation voltage of the conducting/non conducting particle in the SF 6 gas filled electrode gap is high under DC voltage compared with the AC voltage. The levitation voltage increases with frequency of the supply voltage. Particle levitation voltage marginally increases with increase in THD of the harmonic AC voltage. The levitation voltage of the particle increases as and when the barrier is moved towards the high voltage electrode. No polarity dependency is observed on levitation voltage under DC voltages. Percentage of filler content in epoxy nanocomposites has high impact on levitation voltage of the particle. The analysis of levitation voltage with epoxy nanocomposites indicates that up to 3 wt% of MgO added specimen, the levitation voltage is high and above which a marginal reduction in levitation voltage of particle in SF 6 gas medium is observed. The UHF signal magnitude caused by the particle movement process increases with the applied voltage. Also, the extinction voltage of particle movement is lower than the levitation voltage. Also, with increase of applied voltage, on levitation, the magnitude of UHF signal increases. However, on reducing the applied voltage, the UHF signal magnitude is much higher than onward application of voltage. This characteristics is almost the same under AC and DC voltages. The FFT analysis of UHF signal formed due to particle under AC and DC voltages, at the point of inception has dominant frequency at around 1 GHz. When the applied voltage is increased, especially under DC voltages, the FFT analysis of UHF signal formed indicates energy content in the band 2-3 GHz is increased, indicating indirectly, the rate of charge transfer due to particle movement with opposite electrode is high under DC voltages. The FFT analysis of UHF signal formed by non-conducting particle under high frequencies have the energy content increased in the range 2-5 GHz. PRPD analysis indicates that PD activity is observed in the entire phase of the applied AC voltage, irrespective of harmonics and THDs. The number of PD occurrence is high where the rate of rise of supply voltage is high.
Guvvala et al. (Wed,) studied this question.