Electricity and Control September 2022

MEASUREMENT + INSTRUMENTATION : PRODUCTS + SERVICES

Moisture measurement in SF6-insulated switchgear is essential – and WIKA has improved the performance of the GDHT‑20 sensor specifically for this industry. The transmitter, which also provides values for gas density, pressure and temperature, now measures the dew/frost point with an accu racy of ±2 K. Andre Dahlheimer – Product Manager, WIKA Alexander Wiegand SE & Co, says moisture, together with density, are the cru cial parameters for assessing the condition of the SF6 gas used in the switchgear. The GDHT-20 continuously monitors moisture High-accuracy moisture measurement in SF6 switchgear

The GDHT-20 monitors moisture content in the gas, as well as density.

content in the gas. The information from the online monitoring forms the input for a downstream trend analysis. The more precise the density and the moisture measurements are, the more precise this analysis will be. Enabling predictive maintenance The analysis shows the operator when the SF6 will reach a crit ical state and when remedial measures must be taken. As a re sult, maintenance work or gas treatment can be undertaken only when action is needed. Predictive maintenance thus replaces the sequence of regular maintenance previously necessary to avoid ecological and safety risks. Too much moisture in the gas compartment is one of these risks. In older plants, moisture increases mainly due to permeation through sealing materials. In newer plants, it is usually a conse quence of moisture remaining on metal surfaces or in insulation materials during tank assembly, due to incomplete evacuation be fore 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 peo ple’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 humidity in the air 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 config ured 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 suitable for monitoring density of the alternative insulating gases N 2 , CF 4 , O 2 , CO 2 and 3M™Novec™4710.

For more information contact Wika Instruments. Tel +27 (0)11 621 0000 Email: sales.za@wika.com,Visit: www.wika.co.za

SEPTEMBER 2022 Electricity + Control

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