Gas Detection 5
is electronically modulated with a frequency between f=1-10Hz. DC operation (f=0 Hz) is also possible with different type of IR- Detectors. The gas fl ow through the sample cell is typically 0.1-1 L.min-1
. An integrated pressure sensor measured the real time
situation of p and T inside the sample cell. Then a very precise compensation of the pressure (p) and temperature (T) infl uence is possible. The IR-Detector consist of two detector elements for reference and measurement signal generation. In front of each detector element a narrow bandpass interference fi lter is located.
temperature measurement is therefore carried out directly in the cuvette so that the true pressure and temperature values can be measured. Compensation takes place between p=600-1200 hPa and T=5-45°C. This means that error-free measurements can be carried out at high altitudes up to 4000 meters. The detection limit is <0.1vol.% (@zero) and <0.5vol.% (@span).
Conclusion NDIR technology has proven itself for measuring SF6
GIS systems. The
INFRA.sens®
purity in product range is characterized by
high accuracy and stability compared to comparable OEM gas sensors. By integrating this technology into the proven Rapidox series measuring devices, the measuring characteristics have been signifi cantly improved. The possible applications of this device technology have also been expanded.
Early Leak Detection: SF6 leaks can compromise the insulation
of GIS, leading to potential failures. Early detection through continuous monitoring allows for immediate rectifi cation, maintaining system integrity and reducing repair costs.
Figure 4: Optical arrangement of the NDIR Gassensor (
INFRA.sens® ).
Figure 2: The Rapidox SF6 sensors (
INFRA.sens®
). NDIR Gas Sensor
Sulfur hexafl uoride can be measured with a high selectivity in the IR spectral range of 10-12µm. Cross-sensitivities due to gases present in the ambient air (e.g. CO2
+H2 and H2
In Figure 3 we can see a strong absorption line of SF6 to CO2
Lambert-Beer law, as shown in Equation 1. [1] Figure 5:
INFRA.sens® with
I(c) = Intensity at the detector side with Nitrogen (zero gas) I0
= Intensity at the detector side without SF6 α = Coeffi cient of absorption [cm-1
] c = SF6
TM p0
= Pressure in the application [hPa] Since the absorption coeffi cient α of SF6
pM is very high in this
spectral range and the concentration is also present up to 100 % by volume, small measuring cells (1-5 mm) are suffi cient. The optical arrangement is shown in Figure 4. The IR-radiation source
gas concentration inside the sample cell [vol.%]
L = sample cell length [cm] T0
= Temperature during calibration process [K] = Temperature in the application [K]
= Pressure during the calibration process [hPa] gas (I0 =1)
The downstream signal processing electronics process the raw signals into a linear display of the SF6
gas concentration.
Typically, the non-linear sensor signals are linearized by a higher order polynomial (see Fig.6). As the measuring range of 90-100 vol.% SF6
is particularly interesting and important impurity control,
particularly accurate compensation calculations are carried out in this concentration range. This means that the individual errors in this important concentration range are all less than 1% F.S.
As the characteristic curve is very steep between 90-100 vol% SF6
, the temperature and pressure infl uences are very large. Therefore, the compensation of these error infl uences must be carried out very carefully. The simultaneous pressure and
Regulation (EU) No 517/2014 of the European Parliament and of the Council of 16 April 2014 on fl uorinated greenhouse gases and repealing Regulation (EC) No 842/2006 Text with EEA relevance
EPA US Environmental Protection Agency, Sulfur Hexafl uoride Basics:
https://www.epa.gov/eps-partnership/sulfur-hexafl uoride- SF6
-basics
Heise, H.M.: Gas analysis by infrared spectroscopy as a tool for electrical fault diagnostics in SF6
J. Anal. Chem. 358(7), 793-799 (1997) Kahrizi, L: SF6
measurement guide, CIGRE-Publication (2018) insulated equipment. Fresenius for 0-100 vol.% SF6 including the complete
signal processing electronic as well as the temperature and pressure compensation.
O) can thus be excluded. compared
O. Radiation absorption can be described by the Analyzer portfolio using Wi.Tec SF6 NDIR gas
• Operational Effi ciency: By ensuring that the gas insulation levels are optimal, gas monitoring systems help maintain the operational effi ciency of switchgear, thereby preventing unplanned outages.
• Compliance and Environmental Protection: With SF6 being
a signifi cant greenhouse gas, monitoring its levels is crucial for compliance with environmental regulations. NDIR Gas monitoring systems facilitate adherence to these regulations by providing accurate and reliable gas measurements.
• Enhanced Safety: NDIR Gas monitoring systems contribute to safety by detecting gas leaks that could lead to dangerous conditions, ensuring the well-being of maintenance personnel and the facility.
References
Wiegleb, G.: Gas Measurement Technology in Theory and Practice, Springer Verlag Wiesbaden 2023 (https://doi. org/10.1007/978-3-658-37232-3)
Figure 3 : Infrared Spectrum of SF6 Author Contact Details
Dr. Mark Swetnam • Cambridge Sensotec Ltd.
• Address: 29 Stephenson Road St Ives, CAMBS, PE27 3WJ, UK
• Email:
mark@cambridge-sensotec.co.uk • Web:
www.cambridge-sensotec.co.uk
Prof. Dr. Gerhard Wiegleb • Wi.Tec-Sensorik GmbH
• Address: Schepersweg 41-61, D-46485 Wesel, Germany
• Email:
ge.wiegleb@witec-sensorik.de • Web:
www.witec-sensorik.com
Alain Barillet • Wi.Tec-Sensorik GmbH
• Address: Schepersweg 41-61, D-46485 Wesel, Germany
• Email:
al.barillet@
witec-sensorik.de • Web:
www.witec-sensorik.com
READ, SHARE or COMMENTon this article at:
envirotech-online.com/article
in comparison of CO2
and H2
O.
Figure 6 : Calibration curve for 0-100 vol.% SF6
in nitrogen approximated with a polynomial of 6 degrees (Linearization Fitting).
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108
