Sulphur hexafluoride (SF6) is the most popular insulating medium used in gas-insulated switchgear (GIS). SF6, however, has been regarded as a “greenhouse” gas and can cause potential ecological damage. Due to this, monitoring of SF6 present in switchgear, especially for leaks, is a very important activity for any GIS installation. WIKA has been addressing this market globally for over 40 years and is present in India since 2007. We have Vishal Patil, Senior Consultant, WIKA India, discussing technical and practical aspects of SF6, whilst orienting us with WIKA’s solutions in this highly specialized field of SF6 monitoring.
Before we move on to understanding WIKA’s activities in the SF6 domain, please orient us as to why it is important to monitor the density of SF6 stored in switchgear?
It is important to monitor the density of SF6 in switchgear for safety reasons. The filling volume of SF6 gas is defined for each gas compartment and monitored using an SF6 density measuring instrument. In order to prevent system failures in switchgear and network outages, permanent monitoring of the gas density is essential.
Additionally, efficient use of SF6 also means protecting it from moisture. When moisture enters a breaker, the sulphur and fluorine molecules of SF6 grab water’s oxygen molecules to form byproducts during high-temperature episodes. This results in less of the gas to act as insulator. Secondly the resultant byproducts are toxic and corrosive and may harm the switchgear. Hence monitoring of SF6 is very important for efficient service.
We understand that WIKA has various equipments like sensors, switches, etc to measure SF6 density. Tell us more.
WIKA’s provides 360-degree solutions to measure and maintain SF6 in switchgear.
Should the gas density decrease due to leakage, defined alarm contacts in the gas density monitor provide a warning or, if the lower limit is reached, shut the plant down. Modern plant monitoring in the era of the “Smart Grid” requires the use of gas density transmitters with analogue or digital signal output.
The transmitters allow more precise, continuous and central signal monitoring. The signals or data packets sent are permanently monitored by SCADA systems with integrated data storage and data processing. In addition to the gas density measurement, the GDHT-20 multi-sensor can provide pressure, temperature and humidity signals in Modbus® protocol. Alongside the instrumentation, WIKA offers analytic and handling products and connecting parts.
How does one monitor leakages of SF6 in electrical equipment?
Leakages and humidity can be monitored online with the help of WIKA Transmitters GDT-20 and GDHT-20.
In order to prevent system failures in switchgear and network outages, permanent monitoring of the gas density is essential. This transmitter calculates the current gas density from the pressure and temperature using a complex virial equation in the transmitter’s powerful microprocessor. Changes in pressure resulting from thermal effects will be compensated by this and will not affect the output value.
Due to its high long-term stability, the transmitter is maintenance-free and requires no recalibration. Due to the hermetically sealed weld seam and a measuring cell design without sealing elements, the permanent sealing of the measuring cell is ensured. The EMC characteristics fulfil the IEC 61000-4-2 through to IEC 61000-4-6 standards and guarantee an interference-free data output.
The GPU-2000, one of our SF6 solutions, recovers and fills the gas in switchers and cleans the gas of impurities. The GAD-2000is is able to dehydrate SF6 without having to take equipment offline.
Why is online monitoring recommended?
The online monitoring feature is very important as it helps to detect leakages at a very early stage. Also, this feature allows one to visualize the real time conditions on site from one local spot and have access to both live data and historical data at any given point of time. Besides, our analytics will provide density and humidity forecast which help user to plan the maintenance. This simplifies documentation processes thus bringing down the time required for each case of intervention. Overall, the online feature help optimize service capacities by applying “condition based” maintenance.
What is the potential damage caused by SF6 leakage?
This gas does not deplete the ozone layer or cause air pollution. It is, however, almost 24,000 times more effective than carbon dioxide (CO2) at trapping heat, making SF6 a very potent greenhouse gas, contributing to climate change. That’s why it is so important to always monitor the SF6 level in electrical switchgears for leaks.
As an inert gas, pure SF6 does not damage metals. However, if the gas has been contaminated with water, some of the byproducts like thionyl tetrafluoride (SOF4), thionyl fluoride (SOF2), sulphuryl fluoride (SO2F2), sulphur dioxide (SO2), and di-sulphur decafluoride (S2F10) are generated during arc-quenching cycles which are corrosive and may lead to failure of the operating gear in long run.
How has been the general response to WIKA’s SF6-related monitoring devices in the Indian market?
WIKA is selling SF6 gas density monitors (with switches) for the last 40 years worldwide, and in India, since 2007. The demand for the product is good from all GIS/AIS manufacturers. However, SF6 gas online monitoring (IIoT) solutions are yet to make a mark in the market.
Grid operators are still dependent on older technology of SF6 gas density monitors which is giving only switching output, i.e. alarm output and manual reading. For more efficient transmission and distribution, technology transformation is required.
We are sure WIKA GDHT-20 transmitter which offers live measurement and forecast of SF6 density and humidity will be more acceptable as users start understanding the benefits.
Is there any notable difference in WIKA India’s market penetration in public and private sector entities?
At present WIKA has 40 per cent market share in Gas Density Instrumentation and a 60 per cent market share in analytical and leak detection equipment. Public sector utilities are completely dependent on the approval and opinion of GIS manufacturers. Even if they are aware of WIKA’s quality and product variation, they still have to wait for GIS/AIS manufacturers’ approval. In private sector there are no such compulsions and so business demand is definitely better. We hope to serve both the public and private sector with our best possible efforts—thus we are depending on quality for our market penetration.
Coming to a general question, what are the properties of SF6 that makes it a preferred material in electrical equipment?
SF6 is approximately 100 times more effective than air in quenching spurious arcing. Its high thermal heat capacity can absorb the energy of the arc without much of temperature rise.
SF6 effective at quenching the arc generated when switching or opening electrical circuits. It also has very high thermal conductivity, especially at high temperatures, and, therefore, dissipates heat much better than air, nitrogen, helium, or other gases. In addition, equipment insulated with SF6 has lower operating noise, does not emit hot gases, and require relatively little maintenance
From a very practical perspective, do you see a significant phase out of SF6 in the foreseeable future? Which countries today are taking the lead in this direction?
From the clean air point of view, GIS is available at present below 145kV level. By 2030, high voltage switchgear up to 550kV will be replaced by clean air solution. At present European Union countries are taking lead in this direction. India will definitely follow, but it will take time to switch to new technology.
Also read: World’s First Collaboration To Replace SF6 From Existing HV Equipment
Assuming that “clean air” solutions will gradually replace SF6 in the long term, how does WIKA plan to adapt its current SF6-related portfolio of products/services?
At present, we have SF6 density or leakage monitoring solutions in our portfolio for clean air. Shortly we will launch SF6 analysis equipment. We are working jointly with GIS companies for Gas handling solutions. As the market adapts to new technology, WIKA, being a global brand, will be geared up to follow suit and offer the best possible solution to the users.
All photographs in this interview relate to WIKA’s products in the SF6 monitoring domain.
