National Grid Energizes SF6-free 420 kV Gas-insulated Line
Juan de Bedout, GE Power
Global regulations and carbon pricing initiatives are on the rise to limit greenhouse gases (GHGs), spurring innovation from businesses around the world to develop solutions to confront the long-term environmental challenges facing the planet. Governments, academia and businesses are coming together to form strategic partnerships that develop real solutions for reducing the growth of GHG emissions around the world.
At least five years before the famed Paris Agreement took shape, two well respected multinational companies got together to solve a very big problem in the transmission industry: develop and deliver a new environmentally-responsible alternative gas for high voltage (HV) equipment, currently designed with the enormous GHG footprint of sulfur hexafluoride (SF6) gas. The task had to be done without compromising operational performance, reliability or cost.
At that time, power generation, transmission and distribution system operators had no alternative for SF6. The widely-used gas is a man-made, fluorinated gas used throughout the transmission sector due to its excellent gaseous dielectric properties, but it also has a global warming potential (GWP) up to 23,500 times greater than carbon dioxide (CO2) and can remain in the atmosphere for 3,200 years. SF6 concentration in the atmosphere has increased by 20 percent in the past five years. Today, about 10,000 tons of SF6 are installed worldwide annually, of which 80 percent are concentrated in the high-voltage transmission industry. Finding an alternative solution to SF6 is critical to meeting the European Union’s goal to cut GHG emissions from 1990 levels by 40 percent by 2030, and by 80 percent by 2050.
Starting in 2010, GE’s Grid Solutions business collaborated with 3M to develop Green Gas for Grid, (g3, pronounced “g” cubed), an insulating medium for HV switchgear with the same technical performance, same dimensional footprint and same ability to operate in ambient conditions as SF6 (down to -30 C), but with 99 percent less GWP. g3 has demonstrated the ability to match the dielectric strength of SF6, with no voltage limitation, and has shown to be compatible with the standard materials used in HV equipment. It also adheres to all appropriate safety measures, including being nontoxic and nonflammable. Most importantly, an environmental lifecycle analysis shows that g3-gas-insulated substations (GIS) have the lowest total CO2 footprint of all known SF6-free GIS technologies.
GE and 3M believe this milestone technical achievement was a turning point in the transmission industry due to g3’s ability to reduce the environmental impact of HV electrical switchgear above 52 kV at a global scale. But to prove it, the companies enlisted a utility willing to test the gas in their own transmission network.
National Grid Leads the Way
On April 13, 2017, National Grid, a British multinational electricity and gas utility company, successfully energized the world’s first SF6-free 420 kV gas-insulated line (GIL) in its Southeast England Sellindge substation using g3. The new Sellindge substation was deployed in an operationally critical part of the U.K.’s transmission network to help ensure the region would continue to benefit from a safe and reliable supply of electricity, as well as meet voluntary targets set by the utility to reduce GHG emissions across its U.K. and U.S. businesses by 45 percent by 2020 (baseline: 1990). It also plays a vital role in the ElecLink project, which will increase the U.K.’s energy security, reliability and capacity by connecting with the French electricity transmission network.
The introduction of g3 provided an opportunity for National Grid to be at the forefront of new technology development and obtain an early understanding of the equipment’s performance. The estimated gas emissions savings for the project are significant, with more than 7,000 tons of CO2 equivalent set to be saved over the service life of the 230-meter-long, gas-insulated circuits, which connect the substation to the bushings and overhead lines. Replacing just 1kg of SF6 with only half the corresponding mass of g3 is the carbon equivalent of removing 16 cars from the road for one year.
“If we can move to a world where we are not using SF6 at all, this is clearly a better way of managing the problem, rather than using a damaging gas and having to manage it,” said Mark Waldron, National Grid U.K.’s switchgear technical leader.
Because the environmental benefits of g3 do not compromise its technical performance, the implications for this insulating medium across the global transmission network are far-reaching.
Several utilities in addition to National Grid, including SP Energy Networks in Scotland, RTE in France, Axpo in Switzerland, Tennet Germany and 50 Hertz Germany, have already implemented the new gas solution on their own networks. Other utilities from Western Europe, Asia and North America are also using g3. The collective carbon emissions savings from these utilities alone could reach about 25,000 tons of CO2 equivalent, which amounts to preventing more than 27 million pounds of coal from being burned or keeping 5,300 passenger cars off the road for one year, according to GHG equivalency data from the U.S. Environmental Protection Agency.
Beyond limiting global warming to an increase of 2 degrees Celsius, the share of global emissions covered by carbon pricing initiatives, which has increased three-fold over the past decade, will continue to add financial pressure and drive utilities toward future-proofing their businesses. GE conducted a survey of more than 2,000 utilities in 2016 and discovered that 43 percent of them expect to receive a tax or incentive related to SF6 in the next five years, validating the need for a solution like g3 to make its way onto the global stage. g3 is now fully type-tested and commercially available, and the portfolio includes gas-insulated substations up to 145 kV, gas-insulated lines up to 420 kV and air-insulated switchgear current transformers up to 245 kV. The mixture is also available for all HV switchgear manufacturers wishing to develop SF6-free HV products above 52 kV. In addition, there is no patent on the g3 mixture, which allows any manufacturer to develop products with the same mixture based on fluoronitrile, CO2 and O2.
As the benefits of g3 adoption become more well-known and widespread across the transmission sector, the global targets set forth by the United Nations Framework Convention on Climate Change, the Paris Agreement and the Kyoto Protocol will be easier to reach. In the meantime, businesses must continue to work together and invest in cleaner technologies and innovation, develop solutions to enable economic growth while avoiding emissions, and commit to reducing the environmental impact to create a cleaner, faster and smarter tomorrow. | PGI