Very Fast Transient Overvoltages in GIS with Compressed $SF_6-N_2$ Gas Mixtures

Singha, S and Thomas, Joy M (2001) Very Fast Transient Overvoltages in GIS with Compressed $SF_6-N_2$ Gas Mixtures. In: IEEE Transactions on Dielectrics and Electrical Insulation, 8 (4). pp. 658-664.

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Abstract

This paper discusses the characteristics of very fast transient overvoltages (VFTO) in $SF_6-N_2$ gas mixtures at different percentages of $SF_6$. A comparison of the VFTO characteristics of pure $SF_6$ with those of pure $N_2$ is also presented. The investigations are performed using a laboratory model GIS bus duct having a test gap used for simulating a switching event leading to the generation of VFTO. A capacitive voltage sensor is used to measure the VFTO peak magnitude and temporal characteristics. Measurements were carried out at two different gap spacings (0.20 and 0.61 mm) over a pressure range of 100 to 500 kPa. VFTO characteristics for $N_2$, $SF_6$ and $SF_6-N_2$ mixtures obtained from the experiments show similar trends. The level of surge peak magnitude is <2.0 pu for all cases when the gap was 0.20 mm, but it reaches a maximum of 2.41 pu at 0.61 mm gap. At 0.20 mm gap, in $SF_6-N_2$ mixtures, the difference in peak magnitudes is not significant for $10\%$ and $20\%$ $SF_6$ mixtures (between 200 and 400 kPa) and also for pure $SF_6$ and $40\%$ $SF_6$ (between 200 and 300 kPa). The occurrence of corona stabilization during breakdown of the gap may be the cause for such a behavior. Unlike the above observations at 0.20 mm gap, at 0.61 mm gap, the peak magnitudes strictly increase with pressure for the pure gases and gas mixtures. At 0.20 mm gap, the time to breakdown of the gap is found to be almost constant in all cases. But at 0.61 mm gap, the time to breakdown is seen to be dependent on the mixture, pressure, and breakdown voltage, and this observation is in accordance with Toepler's spark law.

Item Type:	Journal Article
Publication:	IEEE Transactions on Dielectrics and Electrical Insulation
Publisher:	IEEE
Additional Information:	Copyright 1990 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.
Department/Centre:	Division of Electrical Sciences > High Voltage Engineering (merged with EE)
Date Deposited:	07 Feb 2006
Last Modified:	19 Sep 2010 04:23
URI:	http://eprints.iisc.ac.in/id/eprint/5311

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