Characterisation and analysis of a corona-stabilised switch filled with environmentally-friendly gas mixtures

Student thesis: Master's Thesis

Abstract

Tests have been completed with the intention of finding an alternative switching medium to SF6 due to environmental concerns. For this purpose, a testing procedure was designed in order to test a novel gas in pulsed power, HFO-1234ze, in mixtures with N2, used as a buffer gas. Thus, decreasing the global warming potential (GWP) of the switching medium from 23900 in SF6 to 6 in HFO-1234ze. The performance of the gas was measured in a specific corona-stabilised switch geometry, characterising triggering range and delay time experimentally, and calculating jitter.Over the testing phase it was shown that N2/HFO-1234ze mixtures were very promising in terms of breakdown strength, with self-breakdown voltages for a 80% N2 / 20% HFO-1234ze mixture at 3 bar gauge reaching up to 32.2 kV and 36 kV for positive and negative polarity, respectively, giving an increase of 191% and 306% breakdown increase from using 100% N2. Furthermore, the triggering ranges recorded reached a maximum of 13.4 kV for positive polarity and 13.6 kV for negative polarity, giving increases of 837% and 174% compared to 100% N2. The delay time and jitter increased accordingly as the total pressure of each individual mix increased.Von Laue statistical analysis was conducted on the delay time data, in order to estimate the relative contributions of the statistical and formative times to the overall delay time. Statistical times were found to increase slightly with pressure, with no clear polarity effect. The formative times were found to form the majority of the overall delay times, increasing with increasing pressure for both polarities.In terms of being a viable replacement for SF6, the gas HFO-1234ze showed positive characteristics in terms of self-breakdown voltage, triggering range and delay time/jitter, in the tested geometry. Although, after testing completion, the electrodes were found to have a layer of carbon which had formed during the testing process; this requires further investigation.
Date of Award1 Oct 2017
LanguageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde

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