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Investigation into CF3I-CO2 gas mixtures for insulation of gas-insulated distribution equipment

Widger, Phillip 2014. Investigation into CF3I-CO2 gas mixtures for insulation of gas-insulated distribution equipment. PhD Thesis, Cardiff University.
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Abstract

This thesis reviews the use of sulphur hexafluoride (SF6) as an insulating medium in the electrical power industry and quantifies the potential global warming effects associated with its continued use. A mixture of Trifluoroiodomethane (CF3I) and carbon dioxide (CO2) is suggested as a potential alternative to SF6, and its insulation properties are examined. Pressure mixture ratios of 10%:90%, 20%:80% and 30%:70% CF3I-CO2 are used in the laboratory test programme. A test rig has been developed to safely fill and recover gas mixtures of CF3I-CO2 in switchgear. Practical medium voltage (MV) switch disconnectors and ring main units are used to test the insulation properties of CF3I-CO2 gas mixtures and compared with SF6 using standard lightning impulses (1.2/50 μs). The experimental mixture ratios are used to identify how the insulation strength varies depending on the content of CF3I used. The switchgear is filled to its normal and minimum operating pressure to observe the reduction in insulation performance of the gas mixtures when the pressure is reduced. The insulation strength is measured using the 50% breakdown voltages (U50) and withstand strengths of each gas mixture in accordance with international standards. The effective ionisation coefficients of various CF3I-CO2 gas mixtures are calculated. This process identified the estimated critical reduced electric field strengths of several CF3I-CO2 gas mixtures. Furthermore, electric field simulations utilised the effective ionisation coefficient functions and the contact geometry of a switch disconnector to predict the likelihood of a flashover occurring for various CF3I-CO2 gas mixtures. This investigation shows that CF3I-CO2 can successfully be used to insulate practical MV switchgear but is dependent on equipment design and operating pressure. It has previously been indicated that by-products of CF3I make it unsuitable to interrupt high current. Therefore, it is suggested in this study that CF3I-CO2 gas mixtures can be adopted to insulate equipment such as vacuum circuit breakers.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Engineering
Subjects: T Technology > TP Chemical technology
Uncontrolled Keywords: CF3I; SF6; Gas Mixture; gas Insulation; Distribution Equipment; Switchgear.
Funders: IET Power Networks Research Academy
Date of First Compliant Deposit: 30 March 2016
Last Modified: 04 Jun 2017 06:47
URI: http://orca.cf.ac.uk/id/eprint/64853

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