Balanced Magnetic Antenna for Partial Discharge Measurements in Gas-Insulated Substations

Recent research has found that Magnetic loop antennas can detect partial discharges (PD) in gas-insulated substations (GIS); however, unbalanced shielded loop (UBSL) antennas are affected by electric field coupling. This research proposes a balanced shielded loop (BSL) adapted for GIS PD sensing with different designs. The frequency response and PD charge estimation for BSL and UBSL antennas are analyzed and compared in a matched test bench using a very-fast pulse calibrator. The results confirmed a better common-mode noise rejection and thus a better charge estimation by using the balanced magnetic antenna. An alternative BSL design improved the antenna's gain by a factor of two, and by using a balun transformer, the gain was increased by a factor of 4. The results showed the criticality in the shielded gap placement and the influence of the antenna's parasitic elements on the balun's frequency response. This paper shows an improvement in the noise rejection using magnetic antennas, which leads to the possibility of better PD sensing in GIS.
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