Problem:
A gas commonly used in electric transformers is also one of the most potent greenhouse gases.
Solution:
See below.
China’s electric grid has a dirty secret: Despite leading the world in renewable energy expansion, it is also the largest emitter of the planet’s most potent greenhouse gas.
Sulfur hexafluoride (SF6) is a synthetic chemical that plays a critical role as an electrical insulator in high-voltage equipment. The gas is odorless, invisible, non-toxic and non-flammable. But it is also a climate killer, 24,300 times more effective at warming the planet than carbon dioxide on a pound-for-pound basis. Once released, sulfur hexafluoride remains in the atmosphere for 1,000 years.
Emissions come primarily from the electric power sector, where the gas is used in circuit breakers and other high-voltage equipment to prevent electricity from arcing. Nearly indestructible, SF6 serves as a critical backstop for any modern electric grid, ensuring that electricity flows only when and where it is needed. However, when electrical equipment in China reaches the end of its useful life, much of the gas is likely vented into the atmosphere.
The use of SF6 has served the electricity supply industry well from the 1970s onwards, due to its excellent electrical insulating properties and even better arc quenching abilities.
Prior to this, vastly complex circuit-breakers were used, which required a large amount of compressed air at high pressure as well as taking up a lot of space. The use of SF6 in transmission switchgear allowed utilities to compact and miniaturise substations, meaning smaller footprints and less obtrusive designs. It has also driven down costs, both in switchgear capital investment and ongoing maintenance.
However, SF6-free switchgear is now becoming commercially available for many transmission applications and this new technology is being developed and adopted by leading utilities, such as National Grid.
How does SF6 contribute to global warming?
Due to its high GWP, SF6 released into the earth’s atmosphere can make a significant contribution to global warming. The global annual emissions of SF6 rose 24% between 2008 and 2018, largely due to the growing use of SF6 switchgear in developing countries.
In 2008 an estimated 7,300 tonnes were emitted globally, which rose to 9,040 tonnes in 2018. To put it in context, 9,000 tonnes of SF6 equates to the greenhouse gas emissions of approximately 44 million passenger vehicles driven for one year, or 103 million tonnes of coal being burned.3
Levels of SF6 released into the earth’s atmosphere are likely to be significantly underestimated, as tracking its release in countries that don’t have reporting requirements is difficult.
Hitachi Energy utilizes a variety of eco-efficient gas mixtures as an alternative to SF6 for its high-voltage portfolio. In its simplest form, the gas mixture is simply a combination of carbon dioxide (CO2) and oxygen (O2). For compact metal-enclosed switchgear, we add a small percentage of a fluoronitrile that helps to increase the withstanding capabilities even further. All the gas mixtures that we use practically eliminate the Global Warming Potential (GWP) of the insulation gas compared to SF6 and help achieve a minimum carbon footprint of the EconiQ product over the complete product life cycle. The gas mixture offers the following advantages:
- It enables the high-voltage equipment to retain the same compactness as SF6.
- Dramatic decrease to the lowest possible carbon footprint: the GWP of SF6 is eliminated and the size and weight of the equipment kept the same – all while delivering identical capabilities and ratings and reliability performance as conventional SF6 switchgear technology, including the switching of capacitor banks and inductors
- Scalable to any required voltage
- Standardized gas handling practices and training similar to SF6, ensuring a smooth, seamless transition to the new equipment
- Widespread acceptance across the industry, leading to superior economies of scale for auxiliary equipment and positive networking synergies