Alternatives to SF6 in HV circuit breaker insulation

Marland, Michael (2014) Alternatives to SF6 in HV circuit breaker insulation. [USQ Project]

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Abstract

Sulphur hexafluoride(SF6) in a synthetic gas extensively used in the high voltage (HV) electricity transmission and distribution industry. The unique and unrivalled properties of SF6 gas that enable it to resist/recover from spark conduction have positioned it as the preferred HV arc interruption medium. Since its introduction in the 1960's HV circuit breakers utilising SF6 have provided less frequent maintenance requirements and reduced installation footprints compared to their Oil/Air predecessors.

Unfortunately however, SF6 has an extremely high global warming potential (GWP), 22,800 times that of carbon dioxide. This high global warming potential combined with a long shelf life (3000 years of atmosphere) has seen the gas identified as one of the six most content contributors to climate change. Additionally, the decomposition by-products of SF6 used for arc extinguishment threaten the occupational health and safety of maintenance staff.

A case study examining the use of SF6 in the region of Central Western NSW has been undertaken as a part of this dissertation. The Central Western NSW electricity grid was found to utilise 10,216k kg of in-service SF6 gas in its HV circuit breakers and associated apparatus. Additionally, SF6 insulated equipment was found to contribute a growing 70% market share of switchgear applications 66 kV and above. A government prescribe annual leakage rate of 0.89% of capacity combined with handling losses suggests the case study area's SF6 insulated equipment is responsible for 2,905 tonnes of C02 equivalent emissions per year.

Alternatives, eliminating or reducing the use of SF6 insulation in HV circuit breakers and associate apparatus do exist and in some cases are fast becoming the more popular and cost effective option. Established solid-dielectric/vacuum and dry-air/vacuum circuit breakers are two such alternatives eliminating SF6 reliance in the 66 kV and below spectrums. Other advancements include non-conventional current transformers with digital outputs that are revolutionising traditional circuit breaker installation concepts.

The 40 year dominance associated with SF6 insulated switchgear is placing utilities in vulnerable positions. With the ongoing replacement of obsolete oil designs expected to finalise in the next decade Australian circuit breakers 66 kV and above could be near 100% SF6 insulated by 2025. Despite a recent fall in national electricity demand, infrastructure upgrades and the diversifying renewable generation mix are supporting continual SF6 insulated equipment growth. Environment driven regulated SF6 price rises or application bans are of increasing concerns to network utilities.

This dissertation provides reasonable and practical recommendations of pro-active technology implementations and trials that will help alleviate reliance on SF6. The proposals also seek to respect restricting network operating budgets recently implemented in an effort to curb rising electricity commodity prices whilst simultaneously offering environmental and OH&S beneficial alternatives.


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Item Type: USQ Project
Item Status: Live Archive
Additional Information: Bachelor of Engineering (Electrical) project.
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Mechanical and Electrical Engineering
Supervisors: Helwig, Andreas
Date Deposited: 09 Sep 2015 00:00
Last Modified: 03 Mar 2016 04:22
Uncontrolled Keywords: SF6, sulphur hexafluoride, HV circuit breakers, global warming potential (GWP)
Fields of Research : 09 Engineering > 0906 Electrical and Electronic Engineering > 090601 Circuits and Systems
URI: http://eprints.usq.edu.au/id/eprint/27073

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