Experimental Assessment on Air Clearance of Multiple Valve Unit Considering Switching Impulse and DC Superimposed Switching Impulse

Jae-Hong Koo, Jae-Kyu Seong, Ryul Hwang and Bang-Wook Lee
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Jae-Hong Koo: Department of Electronic Systems Engineering, Hanyang University, Ansan-si 15588, Korea
Jae-Kyu Seong: Power & Industrial Systems R&D Center, Hyosung Corporation, Ansan-si 14080, Korea
Ryul Hwang: Department of Electrical and Electronic Engineering, Hanyang University, Ansan-si 15588, Korea
Bang-Wook Lee: Department of Electrical and Electronic Engineering, Hanyang University, Ansan-si 15588, Korea

Energies, 2020, vol. 13, issue 11, 1-13

Abstract: Multiple valve unit (MVU), which converts AC to DC and DC to AC, is one of the key elements of high voltage DC (HVDC) transmission. Therefore, the insulation design of MVU against overvoltage should be considered for the stable and reliable operation of HVDC transmission system. Especially, the air clearance of MVU should be calculated based the switching impulse, since it is fatal to MVU in terms of electrical insulation. However, the previous studies were limited to wave front, and the air clearance of the switching impulse is specified only for an ultra-high voltage (UHV) above 750 kV. As a result, it is difficult to calculate the air clearance of MVU which must endure for a switching impulse under 750 kV. In addition, when the switching impulse introduced while the MVU is in normal operation, it is superimposed to DC and creates the most severe situation, but the studies on such subjects are also insufficient. Therefore, as a fundamental step to calculate the air clearance of MVU, the dielectric characteristics of switching impulse and DC superimposed switching impulse in air have been investigated. The experiments on switching impulse showed that the critical flashover voltage was varied according to the curvature of electrode in the gap distance, up to eight times of the electrode radius. However, beyond that gap distance, the critical flashover voltage became similar, regardless of the radius of electrodes. In case of the superimposed experiment, it was performed according to DC pre-stress level and the polarities of switching impulse. The results were most severe when the positive switching impulse was superimposed on the positive DC, and the peak voltage at which flashover occurs was independent of DC pre-stress.

Keywords: air clearance; critical flashover voltage; DC; DC pre-stress; dielectric characteristics; HVDC; multiple valve unit; superimposed; switching impulse (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2020
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