Dielectric Design of Current Lead Parts for a 154 kV Superconducting Apparatus
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O R I G I N A L PA P E R
Dielectric Design of Current Lead Parts for a 154 kV Superconducting Apparatus Jeong Il Heo · Jong Gi Hong · Seokho Nam · Hyoungku Kang
Received: 5 November 2012 / Accepted: 1 December 2012 / Published online: 30 December 2012 © Springer Science+Business Media New York 2012
Abstract Currently, studies on the development of high voltage superconducting machines are being conducted actively in many research institutes all over the world (Kang et al. in IEEE Trans. Appl. Supercond. 17:1493–1496, 2007). In this paper, a sub-cooled liquid nitrogen cooling method is considered to design current lead parts for a 154 kV superconducting apparatus because of its excellent dielectric and mechanical characteristics (Kang et al. in IEEE Trans. Appl. Supercond. 17:1493–1496, 2007). Insulation gases such as SF6 , CF4 , and N2 are considered as suitable pressurization gases for enhancing the dielectric characteristics of a superconducting system in the Republic of Korea (Kang and Ko in IEEE Trans. Appl. Supercond. 21:1332–1335, 2011). Dielectric experiments are conducted on GFRP (glass fiber reinforced plastic) and insulation gases (SF6 , CF4 , and N2 ) with various pressures to establish experimental criteria for designing current lead parts for superconducting applications. It is found that the criteria for calculating electrical breakdown voltage at sparkover of GFRP and insulation gases conform to the mean electric field intensity and the maximum electric field intensity, respectively. Also, the criteria for calculating the electrical breakdown voltage at sparkover according to various conditions are derived. Finally, the conceptual dielectric design of current leads for a 154 kV superconducting apparatus by applying the presented criteria is performed considering various safety factors.
1 Introduction In this paper, a study on the dielectric characteristics of solid and gaseous insulation media is conducted to design the 154 kV current lead parts with a sub-cooled LN2 cooling system. In a sub-cooled LN2 cooling system, the electrical insulation design for current lead parts is important because the dielectric performance of gaseous insulation medium is inferior to that of LN2 [1]. In the Republic of Korea, SF6 , CF4 , and N2 are taken into consideration as promising insulation media for enhancing the dielectric performance of the sub-cooled LN2 cooling system [2]. Also, GFRP is known as the most promising solid insulation material for cryogenic applications. Therefore, dielectric experiments on the solid insulation medium, GFRP as well as the gaseous insulation media are conducted in this paper. The electric field intensity at sparkover on AC and lightning impulse voltage are derived. Also, a condenser-type bushing is considered in the design of current lead parts to uniformize the distribution of electric field intensity for improving the dielectric stability. The thickness of GFRP surrounding the current lead is calculated considering a safety factor. Finally, the conceptual insulation design of 1
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