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Title: Elimination of SF6 from transmission system equipment
Author: Cai, Xiaolei
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2013
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Sulphur hexafluoride gas is the dominant insulation and interruption material in high voltage gas insulated substation. Its usage remains a concern of transmission system operators owing to the global warming potential of the gas. The work carried out in this thesis aims to find the environment-friendly materials that can replace SF6. These candidates are required to have a strong dielectric strength for high voltage busbar insulation and well arc extinguishing capability necessary for high voltage circuit breaker.A range of alternative insulation types including CF3I gas and its mixture, high pressure air and solid insulating foam are considered as substitute of SF6. Theoretical studies on the dimensions of busbars used in substations are carried out for these options. The dimension of the dielectric system and its ampacity of respect system are calculated using heat transfer models considering their boiling point and proper working pressure which is related with the dielectric strength of some gas.On the other hand, SF6 gas circuit breaker is extremely popular on the medium and high voltage power networks owning to its effective arc extinguishing performance. It would be ideal if a substitute material could be found for SF6 as an interruption material. Biodegradable oil PTFE ablation, other gas candidates including N2, CF3I are investigated as possible replacement of SF6 through literature study.The usage of vacuum circuit breaker is eventually capable to operate in high voltage transmission system. Simulations have been carried out with software ATP/EMTP to investigate the influence of different characteristics of vacuum circuit breaker including chopping current level, the dielectric strength of vacuum gap and the opening time. And then the probability of overvoltages when vacuum circuit breakers installed is studied by statistical study in MATLAB.
Supervisor: Cotton, Ian Sponsor: National Grid
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: SF6 gas insulated switchgear ; CF3I, Polyurethane foam ; Vacuum circuit breaker, Transient