SF6 Gas Detection For HV GIS Switchgear – Crowcon F-Gas Detector

Published 30 Sep 2020


The Rise, Risks & Safe Detection Of SF6 Gas

50 years ago ABB pioneered GIS technology.

Gas insulated high voltage switchgear (GIS) is a compact metal encapsulated switchgear consisting of high voltage components, including circuit-breakers and disconnectors, which can be safely operated in confined spaces.

Sulphur Hexaflouride (commonly referred to as “SF6”) is an inorganic, colourless, odourless, non-flammable, heavy gas that has exceptional electrical insulation performance.

Gas detection is specifed for safe monitoring and measurement of SF6 levels on HV & EHV Gas Insulated Switchgear (GIS) and Transformer rooms, 66kV-220kV. Detectors are located inside protected switchgear rooms to provide accurrate monitoring of gas concentrations – usually located in the local gas detection panel, fire protection system or control panel.

SF6 Rules OK!

Sulphur-hexafluoride (SF6) is an excellent gaseous dielectric for high voltage applications that does not react with materials commonly used in high voltage circuit breakers, substations and electrical equipment in the power industry. The combined electrical, physical, chemical and thermal properties offer many advantages when used in HV power switchgear :

SF6 Gas Crowcon Gas Detectors

  • high dielectric strength
  • unique arc-quenching ability
  • excellent thermal stability
  • good thermal conductivity


SF6 Gas In MV & HV Switchgear

SF6 gas has virtually replaced oil and air as the dielectric insulator in medium (MV) and high (HV) circuit breakers, switchgear, gas-insulated substations and electrical equipment.

Despite SF6 being an inert gas during normal use, when electrical discharges occur through the operation of high voltage equipment insulated with SF6, highly toxic by-products are produced that pose a serious health threat to workers.

Furthermore, SF6 gas has been identified as the most potent and persistent greenhouse gas in existence with a global warming potential.

“In addition to protecting personnel from toxic gas risk, installing F-Gas detectors in HV switchgear applications offers a number of benefits,” states Andy Avenell, Fixed Gas Detection Systems Business Development Manager, Crowcon Detection Instruments. “It provides an early warning that the gas is leaking and thus maintains system efficiency and reduces potentially huge gas replacement costs. It enables the supplier and user comply with the relevant sections of the mandatory F-gas regulations. It also helps to reduce the risk of leakage of powerful greenhouse gases into the environment.”

ABB ELK-5 Gas Insulated Switchgear Up To 1200kV

ABB ELK-5 Gas Insulated Switchgear Up To 1200kV


Crowcon F-Gas SF6 Gas Detector

The Crowcon F-gas detector for sulphur hexafluoride (SF6) is ideal for GIS switchgear applications and is part of the Crowcon fixed gas detector range.

Crowcon F-gas provides a lower total cost of ownership by providing fast, stable and dependable SF6 gas detection performance with infrared technology.

Crowcon F-Gas SF6 Gas Detector

Crowcon F-Gas SF6 Gas Detector

In EU regulation 842/2006, leakage control and regular checks on fluorinated greenhouse gases (F-gases) usage are mandated.

Effective monitoring and detection of these gases is essential. SF6 has a very high Global Warming Potential (GWP), 22,200 times higher than CO2.

Therefore, a small amount in the atmosphere can have a large effect on global temperatures.

Although SF6 is not generally considered toxic, it has an short term exposure limit of 1000ppm. As the gas is so heavy in comparison to air, it is also considered by some to present a substantial suffocation risk, because once inhaled, it is hard to expel from the lungs.

Gas leakage can also mean a substantial economic cost to the industry, since F-gases are very costly chemicals to replace.

The Crowcon F-Gas Detector utilises a high quality infrared (IR) sensor specifically calibrated to detect the F-gases commonly in use. The tri-coloured LEDs that indicate the operating status make it is easy to operate. Push-button controls facilitate simple adjustments like zeroing and calibration.

The Crowcon gas detector product requires very little maintenance; a bi-annual gas check can be quickly and easily performed using the keypad and indicator.

Housed within an IP54 rugged enclosure, as part of a compliance system, these Crowcon F-Gas Detectors are usually connected to a building control system.

The output signal can be set to suit virtually any control system – it operates from 24Vdc nominally, and provides a 4-20mA signal.

As there are no consumable parts within the Crowcon F-Gas detector, product longevity and service is guaranteed.

T&D, an approved distributor for Crowcon, can help with any of your gas detection requirements – contact us today.

SF6 Gas Detection In Confined Spaces – Expert OpinionConfined Space Training Command Training Corps

Command Training Corps are specialists in Confined Space training, standbys and consulting – they exist to make dangerous work safer. CTC staff are rescue professionals who have dedicated their lives to being on the cutting edge of best practices in Confined Space work.

We therefore asked Dan Hudson (Owner – Command Training Corps) to provide expert advice and insight into the risks and detection of SF6 gas.

“A standard 5-gas monitor configured for confined spaces would not be sufficient to adequately monitor a space that has housed SF6, or is adjacent to SF6 housing, because traditionally it would not have an F-Gas sensor.  If entry were to be made for repairs or maintenance, monitoring for SF6 would be critical as the gas will displace air, resulting in an asphyxiation hazard for workers.”

“Equally problematic is that SF6 will, under normal operating conditions, produce hazardous decomposition products when exposed to electrical discharges. The most dangerous of these fluoride by-products is disulfer decafluoride, a colourless gas or liquid that is highly toxic, but produces few immediate physical side effects, making it difficult to detect exposure. To make matters worse, it doesn’t take much S2F10 to cause harm; the Permissible Exposure Limit – TWA is only .025 ppm and 1 ppm is considered Immediately Dangerous to Life or Health (IDLH). Therefore, always treat a space that could have SF6 in it as a legitimate atmospheric hazard and monitor for fluorides.”

“When performing gas monitoring on a confined space, remember to obtain readings before ventilating the space; once ventilation has begun, it may be extremely difficult to detect an active leak. Even when a confined space has been determined to be clean, best practices call for the space to be continuously monitored and ventilated while entry is being performed.”

“In addition to using an F-Gas Detector, confined spaces with a potential exposure to SF6 should be monitored for their O2 content (remember that if there is less than 20.9% O2, something is displacing the oxygen). Also, the presence of combustible gases should be monitored. When monitoring using a sampling wand, a helpful rule of thumb is to allow 2 seconds delay for every foot of tubing to the wand (consult your owner’s manual for the specs on your particular monitor).”

“Thus, monitor readings from a 10 foot remote sampling wand will have a 20 second delay. Make sure to measure each layer of the compartment (high, middle, low) long enough to determine an accurate reading. In the case of SF6, because it is 5 times heavier than air, it will behave almost like a liquid and flow into low spaces; extra care should be taken to measure the O2 levels in the lowest parts of the space.”

“As always, workers should determine the appropriate level of PPE when working in confined spaces.  When working around SF6, if you encounter any powdery deposits, you should treat these as hazardous, toxic products of decomposition and quickly remove them with an approved vacuum fitted with HEPA filters.”

Gas Detection For Underground Cable ChambersCrannis Technology Services

Putting safety first in the electrical contracting industry, irrespective of voltage, necessitates a responsible attitude to gas detection.

For instance, Crannis Technology Services a leading UK based Electrical & Data Installation Specialist, use Crowcon Gas Detectors for safe working in underground cable chambers and confined spaces.

Darren Crannis (MD of CTS) comments : “CTS contract to the UK’s largest telecommunications provider for electrical inspection and installation works. It is compulsory that we use a 4-head gas detectors when accessing cable chambers, cable pits and confined areas.”

“We use Crowcon Portable Tetra-3 gas detectors, they are easy to use, have a long operation life (14 hours) and give a constant audio monitoring signal for peace of mind, as well as a 95dB audio detection warning if an alarm is triggered.”

“The risk of an unsealed cable duct causing a leakage of gas into a cable chamber, or poor oxygen levels could have a devastating effect on the health of our employees, so when accessing underground cable chambers and cable “pits”  we use the Crowcon Portable Tetra 3 to first sample and check for harmful gasses and then to constantly monitor the air quality for the safety of our employees.”

Crowcon Portable Gas Detector – Tetra 3 

4-head portable gas analyser which monitors

  • O2 Levels (Oxygen)
  • CH4 (Methane)
  • H2S (Hydrogen Sulphide)
  • CO (Carbon Monoxide)

Crowcon Tetra 3

Cable Chambers

When external cables reach a telephone exchange they enter the building via a large entry plate into an underground room called a cable chamber. In smaller exchanges the cables sometimes arrive in an underground chamber and then are fed to the MDF via a shallow cable trench.

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