Green Power is a very popular phrase in today’s world. However, from generation to distribution through transmission, electricity offers many opportunities to adopt green practices – and literally the scope is increasing with growing penetration of our understanding. However, in this article, we will restrict ourselves to delve into the green ways of energizing and de-energizing electrical circuits and equipment.
As per the dictionary definition, a switch is a device for making and breaking the connection in an electric circuit, whereas a switchgear is composed of electrical disconnect switches, fuses or circuit breakers – used to control, protect and isolate electrical equipment.
Thus, a switch needs to be operated manually; it is designed to switch power on and off. But, a switchgear plays a much more comprehensive role. It is used both to de-energize equipment to allow work to be done and to clear faults downstream. The circuit breaker inside the switchgear breaks the circuit in an overload or faulty condition.
Development of switchgears
The history of switchgears is as old as the beginning of electricity generation. As per Wikipedia, “The first models were very primitive: all components were simply fixed to a wall. Later they were mounted on wooden panels. For reasons of fire protection, the wood was replaced by slate or marble. This led to a further improvement, because the switching and measuring devices could be attached to the front, while the wiring was on the back. The tumbler switch with ordinary fuse is the simplest form of switchgear and was used to control and protect lights and other equipment in homes, offices etc. For circuits of a higher rating, a High-Rupturing Capacity (H.R.C.) fuse in conjunction with a switch might have served the purpose of controlling and protecting the circuit.” However, such switchgears could not be used profitably on high voltage systems. Thus, the race of improvement continued.
“g³ was a natural choice for Evonik. Not only do the g³ products offer us the same reliability and ease of handling as our previous SF6 equipment, they will go a long way in helping us reach our goal of halving our absolute Scope 1 and Scope 2 greenhouse gas emissions by 2025.” – Jürgen Bücker, Head of Regulation
Management Energy Networks at Evonik
Outdoor switchgears are generally used for voltages beyond 66 kV. As they are insulated by air, they need a very large space. Thus, the better (less space) option is Gas-Insulated High-Voltage Switchgear (GIS), which is a compact switchgear enclosed in a metal box. So, within limited space, for high voltage power isolation GIS is a better option, and it is now being used in city buildings, on roofs, on offshore platforms, industrial plants, power plants and so on.
We started with reference of Green Power, and as the U.S. voluntary market defines green power as electricity produced from solar, wind, geothermal, biogas, eligible biomass, and low-impact small hydroelectric sources – worldwide people are mostly focused on that, however, ‘Green’ or environment-friendly & safe practices can be implemented at different pockets of generation, transmission and distribution. So, there lies a huge scope in the area of energising and de-energising of a network or circuit. The components or devices used here are also contributing a lot towards building the Green Power Environment. Let us now see some recent examples.
“At Stedin, we believe that acting sustainably is the most important thing. Where possible, we want to reduce the use of SF6 gas in our switchgear. However, the alternatives are limited and more expensive to purchase. This creates a difficult situation for network operators who want to invest while keeping costs as low as possible.” – David Peters, Chief Technology Officer at Stedin
As per Wikipedia, “The first high-voltage SF6 circuit breaker with a high short-circuit current capability was produced by Westinghouse in 1959. This circuit breaker in a grounded tank (called a dead tank), could interrupt 41.8 kA under 138 kV (10,000 MV·A) and 37.6 kA under 230 kV (15,000 MV·A).” Then the trend continued.
A recent survey report by Kenneth Research communicates, “The SF6 Circuit Breaker Market is anticipated to grow with a modest CAGR over the forecast period, i.e., 2020-2025, owing to the growing semiconductor industry, backed by the rising demand for advanced electronic devices.”
A recent report from Markets And Markets states that, “Imperfect joints in the manufacturing of SF6 circuit breakers leads to the leakage of the SF6 gas, which is a choking gas to some extent. At the time of leakage in the breaker tank, the SF6 gas settles in the surroundings as it is heavier than air and this gas precipitation may lead to suffocation of the operating personnel. The arced form of the SF6 gas is poisonous and can be harmful if inhaled. The Environmental Protection Agency (EPA) in the US has taken measures to find a solution to detect the leakage of the SF6 gas in the breaker tank of SF6 circuit breakers, as the leakage is destructive when an arc is formed.”
The report also indicates, “The internal parts of SF6 circuit breakers require exhaustive cleaning during periodic maintenance under clean and dry environment. The sensitive parts of the device are damaged – if not cleaned at a regular interval. Special amenities are required for the transportation and maintenance of the quality of this gas. Any deterioration in the quality of the gas would affect its performance, which, in turn, would affect the reliability of SF6 circuit breakers. The innovation of SF6 proved to be a challenge for the circuit breaker and fuse industry, which needs to be addressed by the industry players and technical experts in the industry.” So, obviously, it’s the high time when these issues must be addressed…
Towards the green path
Last year, in Hanover fair, ABB exhibited the air-insulated switchgear UniSec as a completely SF6-free switchgear solution for networks up to 24 kiloVolt (kV). It uses the HySec AirPlus, a multifunction apparatus, combining the functions of circuit breaker, line disconnector and earthing switch all-in-one, which is now available with AirPlus insulation gas.
According to ABB, “AirPlus is a groundbreaking climate-friendly gas mixture with a 99.99 per cent lower Global Warming Potential (GWP) compared to SF6. AirPlus is the first ‘green’ alternative gas on the market for medium-voltage switchgear and is part of ABB’s ongoing strategy to develop eco-efficient technologies. AirPlus is a gas mixture based on a fluoroketone molecule and more than 80 per cent dry air.”
A few months back, a good news has come from Eaton. The company has declared, “In the coming years, Eaton will supply thousands of SF6-free switchgear systems to network operator Stedin. SF6 gas is one of the most potent greenhouse gases and is still used extensively by the electrical sector for switchgear systems. Stedin has put together plans to expand its electricity network even further over the next few years. A key part of developing these plans was finding a partner to make the expansion as environmentally friendly as possible. The SF6-free installations from Eaton will help Stedin reduce their use of SF6 gas by an average of 1,950 kg of SF6 per year.”
Eaton wants to completely eliminate the use of SF6 gas and has therefore developed the Xiria switchgear. The Xiria is insulated using dry air instead of SF6 gas, and switching is carried out using a vacuum interrupter. The Xiria can switch more than 10,000 times, making it particularly suitable for applications where the switch needs to be actuated several times a day, such as wind farms and solar parks generating renewable energy.
Being in the same race, GE Renewable Energy’s Grid Solutions business has secured its first ‘Green Gas for Grid’ – or ‘g³’ (pronounced ‘g-cubed’) – industrial orders. Together, German’s specialty chemicals leader Evonik and UK’s Omexom, an Engineering Procurement and Construction (EPC) company, recently ordered a total of 18 g³ Gas Insulated Switchgear (GIS) bays.
g³ is GE’s game-changing alternative to SF6. g³ products feature the same high performance and reliability as SF6 equipment but have a gas mass with more than a 99% reduced CO2 equivalent value. More importantly, Life-Cycle Assessments (LCAs) have shown that g³ products have a greatly reduced CO2 impact on the environment compared with SF6 products. Additionally, g³ products do not cause pollution transfers to other environmental indicators because they have the same compact dimensions as traditional SF6 products.
There are many other initiatives from the big as well as small players. However, still the demand for SF6-based switchgears is quite high. The question that arises at this point is: how far in the short-run the users will be ready to spend for SF6-free technologies in the post-COVID 19 pandemic era, with the dwindled down economic status?
By P.K Chatterjee, Editor, Electrical India