Breaker breakthrough

Above: Hitachi Energy’s 420 kV EconiQ™ SF6-free circuit-breaker

The new breaker, which has passed all relevant tests described in the IEC and IEEE standards for 63 kA, 5000 A, 50 and 60 Hz, marks attainment of a significant milestone in the EconiQ™ accelerated roadmap, announced by Hitachi Energy at CIGRE Session 2021 (see Modern Power Systems, Nov/Dec 2021, pp 51-53). The roadmap sets out Hitachi Energy’s development timetable for its EconiQ™ portfolio of SF6-free high voltage breakers and switchgear.

The company says it has been investing in eco-efficient alternatives to SF6 for over two decades and its achievements include the world’s first 170 kV eco-efficient gas-insulated switchgear.

Over time, it has been working to steadily increase the voltage levels of its SF6-free offerings, with current interruption being the biggest technical challenge. Initially, the focus was on gas mixtures employing fluoroketones, but in April 2021 Hitachi Energy (then called Hitachi ABB Power Grids) announced a cross-licensing agreement with GE relating to the use of fluoronitrile based mixtures as an alternative to SF6 (see Modern Power Systems, May 2021, p 20). These mixtures and the compactness and performance they deliver are a key feature of EconiQ™.

The 420 kV circuit-breaker is a fundamental enabling technology for further expansion of the SF6-free HV portfolio, and will be used in both dead tank breaker (DTB) and future GIS applications. The EconiQ™ 420 kV DTB and GIS are expected to be released at the end of 2022, on track with the Hitachi Energy roadmap for SF6 elimination.

Hitachi Energy plans to install the world’s first EconiQ™ 420 kV circuit-breaker by mid 2023, as part of an SF6-free 420 kV dead tank breaker, also a world first. This installation will be for Eversource in New England, USA, at one of its 345 kV substations. Hitachi Energy says the EconiQ™ 420 kV DTB will be just as reliable as SF6 based DTB technology.

The use of fluoronitrile-based gas mixtures as an alternative to SF6 in high-voltage equipment has led to the development of a “game-changing solution that the industry will likely converge upon,” says Hitachi Energy. It believes the technology is game changing because it “retains the best of SF6 and is 100% as reliable as the conventional solution while reducing equipment size, materials and carbon footprint throughout the product lifecycle” and this “unlocks the acceleration of eco-efficient alternatives to SF6 in the industry, which will support the widest range of applications in switchgear.”

Hitachi Energy is using/will use fluoronitrile-based gas mixtures for gas-insulated switchgear, dead tank breakers, hybrid switchgear and current transformers for both indoor and outdoor applications, down to -30°C. For some other applications, such as SF6-free live tank breakers, Hitachi Energy considers a CO2/O2 mixture “the optimum choice.”

Q and A with Markus Heimbach, Managing Director, High Voltage Products, Hitachi Energy

What were the main challenges that had to be addressed in developing the 420 kV SF6-free circuit breaker?

From a technology perspective, high-voltage circuit-breakers are the most sophisticated and technically challenging modules in high-voltage switchgear. They are constantly exposed to extreme mechanical and electrical stresses. For example, at the 420 kV voltage level, circuit-breakers are meant to interrupt fault currents in the region of 63 000 A. The energy that needs to be tamed by the circuit-breaker in a fraction of a second is enormous. It is comparable to a car hitting a wall at a speed of around 100 km/h, and for a brief moment, the temperatures inside the circuit-breaker will be hotter than the surface temperature of the sun.

SF6 has excellent insulation and current interruption properties, which enables high-voltage equipment to be as compact as possible. Furthermore, modern SF6 circuit-breakers use gas circuit-breaker technology, which means a gaseous medium is used for both switching (including current interruption) and insulation. Gas circuit-breaker technology is proven to be reliable and scalable. Scalability means that products using the same technology can cover a voltage level from 52 kV up to ultra-high voltage, 1200 kV.

As SF6 is such an excellent gas and so important for the high-voltage grid, it is a big feat to find an alternative gas to replace it at all high voltage levels. For SF6 alternatives, the main challenges are to reach the same performance and scalability as SF6 at similar size.

Size is absolutely critical in modern high-voltage switchgear as installations tend to be near urban centres, where land and space are limited, and substations need to be as compact as possible. To achieve compactness without using SF6, the deep scientific understanding of the process inside the breaker needs to be translated into the design of the circuit-breaker. So far, this challenge has been achieved only for the lower voltage levels, up to 170 kV.

And how were they addressed?

For over two decades we have been investing in research and development in the field of eco-efficient technologies and pioneered the world’s first high-voltage eco-efficient switchgear. We have gained years of field experience from lower voltages and over time, and we have been successful in continuously increasing the voltage levels to 420 kV.

Using gas circuit-breaker technology has enabled us to go beyond 170 kV and to achieve 420 kV with SF6 alternatives. Gas circuit-breaker technology, with its high reliability, also enables us to retain around five decades of experience and knowledge from SF6 developments and technology.

The key to this success is the scientific understanding of the processes inside the breaker, and translating the design rules from SF6 to the new gas mixture, therefore keeping a similar performance and size. As a result, using the fluoronitrile (C4-FN) mixture we can achieve the same compactness as equipment based on SF6.

How significant is this achievement?

This is a historic milestone and ground-breaking achievement for the high-voltage industry. SF6 has been used for decades, and now we have one of the most demanding, high-end, ratings commercially available without the use of SF6.

Eliminating SF6 means eliminating environmental impact and reducing carbon footprint. This proves that fluoronitrile gas mixtures are the future of the high-voltage industry.

The 420 kV circuit-breaker is now fully tested as described in IEC and IEEE standards. The scalability of our technology is proven and we are the first in the world to deliver a 420 kV, 63 kA circuit-breaker free of SF6 – a significant technology achievement in the high-voltage industry. It is also a key milestone in reducing environmental impact. In comparison,
a conventional SF6 420 kV GIS contains around 1200 kg of SF6 per bay, which is around 15 times more than a 145 kV GIS.

This breakthrough technology is the key enabler to unlocking the widest range in high-voltage eco-efficient switchgear applications. With a reliable and scalable technology with the lowest carbon footprint, we are enabling our customers and the industry as a whole to rapidly transition to eco-efficient solutions to advance a sustainable energy future for all.

How do the dimensions/footprint/performance of your fluoronitrile based 420 kV circuit breaker compare with SF6 based predecessors?

The footprint and dimensions are very similar to those achieved with SF6. The new circuit-breaker has in all regards the same performance and the same reliability as the SF6 equipment.

What are the next steps in terms of your EconiQ™ roadmap, and how will the 420 kV circuit breaker technology benefit/be used in other SF6-free equipment (eg DTB, GIS)?

The next steps are to complete the type tests and start commercial production. Thanks to the common platform approach, the 420 kV circuit-breaker will be used in both 420 kV dead tank breakers (DTBs) and 420 kV gas-insulated switchgear (GIS), which are expected to be released before the end of this year, as per our 2021 roadmap. As the technology is scalable, it will be also utilised with some adaptations in other products lines and voltage levels.

You have suggested that the industry is likely to converge on fluoronitrile mixtures. Are we beginning to see signs of that?

Yes, in Europe, two out of three major industry players are already using fluoronitrile gas mixtures to replace SF6. There are also several manufacturers in China and Korea using the fluoronitrile gas mixture. There are IEC standards published or under preparation covering the fluoronitrile gas mixture. The auxiliary and gas handling equipment for fluoronitrile gas mixtures are commercially available from several manufacturers. Hence, there is already an industrial ecosystem around this technology.

In the context of tightening regulations on SF6, eg in the EU, how future proof is fluoronitrile based technology?

We believe that the technology based on the fluoronitriles is the future and the regulations will reflect that. It is the most practical and scalable of solutions available today for voltage levels above 52 kV, and is the only technology to enable a fast phase-out of SF6 while ensuring the transmission grid reliability that is essential to the energy transition.

We are of the opinion that regulations should be technology-centric and take into account the overall environmental footprint of the entire switchgear and the substation.

High-voltage SF6-free solutions that do not use fluoronitrile mixtures are larger in size, resulting in higher impact on the environment as more raw materials are used, and require larger spaces and buildings. The compactness in gas-insulated high-voltage equipment is achievable only with the high dielectric performance that comes from using small quantities of fluorinated gas in the gas mixture. This is a straightforward consequence of fundamental science that is acknowledged by all experts.

After the European Commission published the proposal for possible future F-gas regulations, all stakeholders were invited to comment. Almost all of the relevant high-voltage stakeholders commented in favour of introducing fluoronitrile based solutions. ENTSO-E (European Network of Transmission System Operators for Electricity), the association representing 39 European transmission system operators from 35 countries, wrote in their statement: “TSOs absolutely need technologies with GWP>10 to avoid delaying the implementation of their SF6 phase-out strategies.” This is a strong endorsement of fluoronitrile-based technology.

Is the fluoronitrile gas mixture applicable to the existing fleet?

Insulating gas with fluoronitrile gas mixture is very versatile and additionally enables retrofill of existing gas-insulated lines of SF6 equipment. This helps prevent future SF6 gas leaks in the large installed fleet without exchanging primary equipment. Together with National Grid UK, we have successfully energised a world first pilot in Richborough, UK, replacing SF6 in installed high-voltage gas-insulated lines. EconiQ™ Retrofill is now part of our high voltage portfolio.