PROJECT TITLE :
Asymmetrical AC field emission current characteristics of vacuum interrupters subjected to inrush current
Per the IEC standards, check objects in back-to-back capacitor bank switching tests are subjected to inrush currents of 20 kA peak and 4250 Hz frequency throughout making operations. For vacuum interrupters (VIs), the contact surfaces might be seriously broken by the high-energy arc of the inrush current. The sector emission current characteristics mirror the surface microscopic conditions after undergoing the inrush current. The objective of this paper is to research the impact of the inrush current during back-to-back capacitor bank making operations on the sphere emission current characteristics of vacuum interrupters beneath AC power frequency voltage. The amplitudes of the inrush current were set as ten and 20 kA, respectively. The sample VIs underwent the inrush current at each amplitude twice. After every inrush current, the sector emission current of the VI was measured by applying a power frequency voltage upon the contacts with a mounted gap of 1 mm. By applying an AC power frequency voltage, an unsymmetrical field emission current was measured. Likewise, per the Fowler-Nordheim (F-N) theory, the sphere enhancement issue β and therefore the effective emission space Ae were calculated. The experimental results show that there's a vital unsymmetrical field emission current at each polarity of the ability frequency voltage. Moreover, throughout the voltage rising phase, the sector enhancement factor β is higher and also the effective emission area Ae is smaller than that during the voltage falling part for both positive and negative voltage polarities. A heating-cooling hysteresis impact of the emission sites may explain the phenomena.
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