Sulphur hexaflouride, SF6

Moisture

There are several different units used to present the moisture contained in SF6 gas. Cigre however, recommends the use of ppmw(parst per million in weight). If you need a conversion guide this is specified in the IEE standard 1125-1993.

CIGRE also recommends the following specifications for SF6 dew point meters:

Measuring range 10ppmw to 500ppmw.
Accuracy +/- 20ppmw.
Sensor resistant to oil traces and corrosive gases.
Use of self sealing valve connections.
Portable.
Calibrated or field calibratable.
SF6 gas release less than 1 bar litre per measrmt.
Obtain results within 5 minutes.

SF6 Analyser

Decomposition by-products

Gas flourides such as SF4 and WF6, oxiflourides like SOF2, SOF4 and SO2FO2, oxide S=2 and hydrogen flouride HF are all decomposition by-products. However, one or two of these should be selected as an indicator of the concentration of decomposition products. SO2 and SOF2 are the best choice due to the fact that they represent the biggest fraction of decomposition products.

CIGRE recommends the following specifications for SF6 decomposition by-products analysers:

Measuring range up to 20ppmw
Calibration for So2 and SOF2.
Accuracy +/- 10%.
Use of self sealing valve connections.
Portable.
SF6 gas release less than 1 bar litre per measrmt

SF6 percentage

Air introduced by handling and CF4 that is produced by arc erosion of polymers is measured in SF6 gas concentration in % volume.

CIGRE recommends the following specifications for SF6 % analysers:

Accuracy better than +/- 1% vol.
Response time < 1 min.
No recalibration required.
Separate calibration for air and CF4 mix with SF6.
Portable.
SF6 gas release less than 0.5 bar litre per meas.

Gas multimeter

On-line monitoring of SF6 gas

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