Transient earth voltage (TEV) signals propagate on metal surfaces when partial discharge (PD) occurs due to the deterioration of insulation performance in the operation of gas-insulated switchgears (GIS). A TEV sensor has advantages of high sensitivity and convenient installation for detecting PD defects. However, the TEV sensor depends on imports in domestic and detailed studies have not been conducted. In this study, a sensor was designed and fabricated by the TEV principle and its response characteristics were evaluated for detecting PD defects, which were simulated as protrusion on conductor (POC), protrusion on enclosure (POE), and free moving particle (FMP) defects. Finally, the PD-induced TEV signals were measured and phase-resolved partial discharge (PRPD) patterns were analyzed to identify the type of defect.

Electrode systems: a protrusion on conductor (POC), a protrusion on enclosure (POE), a crack in epoxy plate and a free particle (FP) were fabricated to simulate insulation defects in a gas insulated switchgear (GIS). SF6 gas was filled in the electrode systems by 3 bar and/or 5 bar, respectively. Partial discharge (PD) pulses were detected through a 50 Ω non-inductive resistor. A calibration test was carried out according to IEC 60270, and the sensitivity was 0.25 pC/mV. PD pulses were distributed in the phase of 50˚∼135˚ and over 95% of them existed in the phase of 55˚∼120˚ for the POC. PD pulses were distributed in the phase of 230˚～310˚ and over 90% of them existed in phase of 220˚∼300˚ for the POE. PD pulses occurred in the phase of 40˚∼60˚ and 220˚∼300˚ for the crack, and pulse counts were 25%higher in negative polarity than in positive polarity. PD pulses were distributed in every phase unlike to other three electrode systems and the peak magnitude was measured at 118˚ and 260˚ for the FP. As described above, PD pulses were observed in positive polarity for the POC, in negative one for the POE, in both one for the crack and the FP. In conclusion, it is expected that the identification rate of defect type can be improved by considering the polarity ratio of PD pulses on the PRPDA method.

Citations

• Identification of Partial Discharge Defect Detection in Cast-Resin Power Transformers Using Back-Propagation Algorithm
  Sung-Wook Kim
  Journal of information and communication convergence engineering.2024; 22(3): 231.     CrossRef