7/27/2019 Electrical Engineering Portal.com EEP Recommends

1/2

Fig. 11-1 p-t dia. for p ure SF6 gas

EEP recommends

electrical-engineering-portal.com /sf6-gas-as-insulating-and-arc-quenching-medium

Edvard

Translate

Get PDF

Sulphur hexafluoride gas (SF6) is employed as insulation in all parts of the installation,

and in the circuit-breaker also forarc-quenching . SF6 is an electronegative gas, its

dielectric strength at atmospheric pressure is approximately three times that of air.

It is incombustible, non-toxic, odourless, chemically inert with arc-quenching properties

3 to 4 times better than air at the same pressure.

Commercially available SF6 is not dangerous, and so is not subject to the Hazardous

Substances Order or Technical Regulations on Hazardous Substances (TRGS).

New SF6 gas must comply with IEC 60376 (VDE 0373 Part 1). Gas returned from SF6

installations and apparatus is dealt with in IEC 60480 (VDE 0373 Part 2). SF6 released into the atmosphere is

considered a greenhouse gas.

With its contribution to the greenhouse effect below 0.1%, the proportion of

SF6 is low compared to that of the better known greenhouse gases

(carbon dioxide, methane, nitrous oxide etc.). To prevent any increase of

SF6 in the atmosphere, its use should in future be confined to closed

systems. Devices suitable for processing and storing SF6 gas are

available for this purpose.

The gas pressure is monitored in the individually sealed gas

compartments and in the circuit-breaker housing. The low gas losses

(below 1 % per year) are taken into account with the first gas filling.

Automatic make-up facilities are not necessary. The isolating gas

pressure is generally 350 to 450 kPa at 20 C. In some cases this can be

up to 600 kPa. The quenching gas pressure is 600 to 700 kPa.

Outdoor apparatus exposed to arctic conditions contains a mixture of SF6

and N2, to prevent the gas from liquefying. The pressure-temperature

relationship of pure SF6 gas is shown in Fig. 11-1.

Arcing causes the decomposition of very small amounts of SF6 gas. The

http://webstore.iec.ch/preview/info_iec60376%7Bed2.0%7Db.pdfhttp://electrical-engineering-portal.com/maintenance-of-sf6-gas-circuit-breakershttp://electrical-engineering-portal.com/insulating-materials-in-electrical-equipmenthttp://www.printfriendly.com/print/?url=http://electrical-engineering-portal.com/sf6-gas-as-insulating-and-arc-quenching-mediumhttp://www.google.com/translate?hl=en&sl=auto&tl=es&u=http://electrical-engineering-portal.com/sf6-gas-as-insulating-and-arc-quenching-mediumhttp://webstore.iec.ch/preview/info_iec60376%7Bed2.0%7Db.pdfhttp://www.chemical-check.de/download/TRGS-512-EN.pdfhttp://electrical-engineering-portal.com/download-center/books-and-guides/schneider-electric/sf6-mv-hv-switchgearhttp://electrical-engineering-portal.com/maintenance-of-sf6-gas-circuit-breakershttp://electrical-engineering-portal.com/insulating-materials-in-electrical-equipmenthttp://www.printfriendly.com/print/?url=http://electrical-engineering-portal.com/sf6-gas-as-insulating-and-arc-quenching-mediumhttp://www.google.com/translate?hl=en&sl=auto&tl=es&u=http://electrical-engineering-portal.com/sf6-gas-as-insulating-and-arc-quenching-mediumhttp://electrical-engineering-portal.com/sf6-gas-as-insulating-and-arc-quenching-medium

7/27/2019 Electrical Engineering Portal.com EEP Recommends

2/2

Fig. 11-2 Conversion of water vapou r content

into dewpoint for SF6 gas at atmos pher ic

pressure

ecompos t on pro ucts react w t water, t ere ore t e gas s mo sture

content, particularly in the c ircuit-breaker, is controlled by drying

(molecular) filters.

Careful evacuation before first gas filling greatly reduces the initial

moisture content. Fig. 11-2illustrates the conversion of water vapour

content into dewpoint.

SOURCE: ABB