Miracle gas or not?
There are many published discussions and reports on various aspects of SF6 gas(sulphur hexafluoride) usage in electrical equipment. Most of them are based on facts and researches, but some are not.
By Edvard | November, 10th 2014
34 Questions And Answers To Break the Myth About SF6 Gas In Electrical Equipment
Let’s try to answer the 34 questions and break the myth about this ‘miracle’ gas.
Note that most of answers are based on CAPIEL (Coordinating Committee for the Associations of Manufacturers of Industrial Electrical Switchgear and Controlgear in the European Union) researches and related IEC standards as well.
Your comment is highly appreciated!
1. Where is SF6 used?
The following applications are known. For some of these most probably you haven’t heard of.
For sound insulation in windows,
In vehicle tyres,
For magnesium casting in the automotive industry,
As insulating and arc extinguishing medium in electric power equipment,
For manufacturing of semi-conductors,
In tandem-particle accelerators,
In electron microscopes,
As tracer-gas in mining,
In x-ray material examination equipment,
As purification and protection gas for aluminium and magnesium casting,
In sport shoes,
Medical examinations,
In military aircraft radar systems and other military applications.
2. Is SF6 a health hazard?
Pure SF6 is physiologically completely harmless for humans and animals. It’s even used in medical diagnostic. Due to its weight it might displace the oxygen in the air, if large quantities are concentrating in deeper and non ventilated places.
Legislation for chemicals does not categorise SF6 as a hazardous material.
3. Is SF6 harmful for the environment?
It has no ecotoxic potential, it does not deplete ozone. Due to its high global warming potential of 22.200 (*) it may contribute to the man made greenhouse-effect, if it is released into the atmosphere. However in electrical switchgear the SF6 gas is always used in gas-tight compartments, greatly minimising leakage. This make the real impact on greenhouse effect negligible.
(*) According to the 3rd Assessment Report of UNFCCC. Previous accepted value was 23.900
4. What is the overall contribution of SF6 used in the electrical equipment to the greenhouse effect?
Less than 0,1 % ( see CAPIEL) and <a href="http://www.cigre-sc23b3.org/%20SF6/" target="_blank" title="CIGRE >CIGRE). In an Ecofys study the contribution to the greenhouse effect in Europe is estimated to 0.05 % (*).
(*) ECOFYS, Sina Wartmann, Dr. Jochen Harnisch, June 2005, “Reductions of SF6 Emissions from High and Medium Voltage Equipment in Europe”
5. How wide is the use of SF6 in transmission and distribution switchgear applications ?
SF6 insulated switchgear is currently used world-wide. It is estimated that an average of about 80 % of HV equipment manufactured now has an SF6 content.
6. Why is SF6 used in electric power equipment?
Because of its outstanding electrical, physical and chemical properties enabling significant benefits for the electricity supply network:
It insulates 2.5 times better than air (N2),
Over 100 times better arc quenching capability than air (N2), and
Better heat dissipation than air;
In addition to this, LCA studies have proven that the use of SF6 technology in the electrical distribution switchgear equipment results in lower overall direct and indirect environmental impacts compared to air-insulated switchyards (*)
(*) Solvay Germany, 1999: Urban power supply using SF6 technology, Life cycle assessment on behalf of ABB, PreussenElektra Netz, RWE Energie, Siemens, Solvay Fluor und Derivate
7. What are the benefits of high and medium voltage SF6-switchgear?
There is a significant number of benefits, as follows:
Local operator safety
SF6-insulated switchgear makes a substantial contribution to reduce the accident risk.
The total enclosure of all live parts in earthed metal enclosures provides immanent protection against electric shock and minimises the risks associated with human errors
The high-grade switchgear remains hermetically sealed for its whole service life.
Very high operational reliability
It offers a great operational reliability because inside the enclosed gas compartments the primary conductors have complete protection against all external effects.
The minimal use of synthetics reduces the fire load.
The SF6 insulation ensures complete freedom from oxidation for the contacts and screwed joints, which means that there is no gradual reduction in the current carrying capacity of the equipment as it ages.
There is no reduction in insulation capacity due to external factors.
Important contribution to the security of supply
Total enclosure also means that the equipment is almost completely independent from the environment. SF6 insulated switchgear can also be used under difficult climatic conditions, for example:
In humid areas with frequent condensations from temperature changes, and even in places with flooding potential.
Where the reliability of the insulation might otherwise suffer from contamination, e.g. dust from industry or agriculture or saline deposits in coastal areas. Gas- insulated switchgear completely eliminates this possibility throughout the whole service life of an installation
In contrast to air insulation, whose insulating capacity reduces with increasing altitude, SF6-insulated switchgear retains its full insulating capacity regardless of height above sea level. So larger and more costly special designs, or equipment with higher insulation ratings – and therefore more costly – are avoided
Small space requirement
Due to the high dielectric strength of the gas, the switchgear is compact with space requirements minimised.
The excellent safety and low space requirement of SF6 switchgear allows it to be sited directly in conurbations and close to load centres, such as city centres, industrial manufacturing plants and commercial areas.
Therefore, this fulfils one of the basic essentials of power distribution, namely that substations should be placed as close as possible to load centres in order to keep transmission losses to a minimum, to conserve resources and to minimise costs.
Major savings in building, land and transport costs can be achieved throughout the whole process chain.
In several cases SF6 switchgear is the only possible solution: for wind power plants (offshore), in caverns, for large generator circuit-breakers, and for extensions of existing installations.
This often allows existing buildings use to be extended where switchgear replacement or extension to meet load growth is needed.
Excellent economical and ecological features
Distinct economic benefits come from:
The long service life
Minimal maintenance expenditure thanks to maintenance-free, gas-tight enclosures
Reduced costs for land, buildings, transport and commissioning
Maximum operational reliability as a prerequisite for the remote control and automation of power networks
Ecological and economic benefits arise from:
Minimum transmission losses as a result of placing equipment close to load centres.
Reduced primary energy consumption and emissions contribute to economically optimised power supply systems.
And the long service life of SF6 switchgear also contributes to the conservation of resources.
Aesthetic and ecological benefits for rural and city landscapes:
Because SF6 installations are compact, need minimum maintenance, have extraordinarily high availability and are independent from climatic impacts. They offer not only major ecological and economic advantages but can also be integrated seamlessly in any landscape or architecture of towns, cities or countryside
Reclamation of areas previously taken up by conventional substations.
8. Is there any alternative to SF6 in switchgear for high and medium voltage?
From the LCA point of view no technically and economically viable alternative exists with an equivalent set of properties described above and the same degree of safety and reliability.
”A combination of extraordinary electrical, physical, chemical and thermal properties makes SF6 a unique and indispensable material in electric power equipment for which there is no functionally equivalent substitute.” (Quotation from a CIGRE3 Report) (*)
(*) CIGRE: International Council on Large Electric Systems
9. What are the different applications in electrical power equipment using SF6?
These are the most common applications where SF6 is used:
GIS (Gas Insulated Switchgear for medium and high voltage),
CBs (Circuit Breaker),
Power transformers,
VT (Voltage Transformer),
CT (Current transformer),
RMU (Ring Main Unit),
Assemblies of HV devices and GIL (Gas insulated lines),
Capacitors etc.
10. What is the difference between high-voltage (HV) and medium- voltage (MV) GIS regarding SF6?
Basically there is no difference as both applications use the SF6 in gas-tight compartments with negligible leakage rates. In general the MV (up to 52 kV) use pressures close to atmospheric pressure in sealed pressure systems. Low pressure and small size result in little gas quantities of only some kg. The leakage rate is extremely low, less than 0.1 % per year.
HV switchgear (< 52 kV) use closed pressure systems with leakage rates less than 0.5 %, which is the maximum permitted by the relevant IEC standards. The operating pressure of HV equipment is approx. 5 times highercompared to MV.
To be continued...
For SF6 GIS equipment,it is necessary to use an Ultra High Sensitivity SF6 Trace Gas Leak Detector to find the leak and fault point. D-Industrial Q200, as the quantitative leak detector, as the main detection instrument of SF6 gas leakage of Circuit Breaker, GIS, Transformer and other SF6 equipment, it can detect and alarm SF6 gas leakage and track and locate the leakage quickly. It Is of high sensitivity (10-8 mL/S (0.01 PPM).
