Moisture measurement in SF6-insulated switchgear is essential. That’s why WIKA has improved the performance of the GDHT-20 sensor for this industry. The transmitter, which also provides values for gas density, pressure and temperature, now measures the dew/frost point with an accuracy of ±2 K.
Moisture, along with density, is the crucial parameter for assessing the condition of the SF6 gas used. The GDHT-20 continuously monitors its content in the gas. The information from the online monitoring forms the input for a downstream trend analysis. The more precise both the density and the moisture measurement are, the more precise this analysis will be.
Predictive maintenance instead of regular maintenance intervals
The analysis shows the operator when the SF6 will reach a critical state and when remedial measures must be taken. As a result, maintenance work or gas treatment is only undertaken when action is actually needed. Predictive maintenance thus replaces the sequence of regular maintenance intervals that was previously necessary to avoid ecological and safety risks.
Too much moisture in the gas compartment is one of these risks. In older plants, moisture mainly increases due to permeation through sealing materials. In younger plant, this is usually a consequence of moisture remaining on metal surfaces or in insulation materials during tank assembly, due to incomplete evacuation before initial filling with SF6.
Excessive moisture content leads to corrosive reaction products that can damage internal components and shorten the service life. If such substances escape, there is an additional danger to people’s health.
SF6 moisture measurement parameters
Measurement of SF6 moisture is therefore indispensable. In most cases, the dew or frost point is used as a parameter. This is the temperature at which the air humidity begins to condense. In the case of SF6, the atmospheric dew point specified by IEC 60376 is -36 °C.
The accuracy of the GDHT-20 of ±2 K for moisture measurement is validated at the frost point with an internationally valid reference standard. However, the measuring instrument can also be configured for other parameters (dew point, ppmv, ppmw and relative humidity). The new version of the sensor also features greater application flexibility. The GDHT-20 is now also suitable for density monitoring of the alternative insulating gases N2, CF4, O2, CO2 and 3MTM NovecTM 4710.
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You can also find out more about WIKA’s SF6 expertise in the following video: