When it comes to resilience, vacuum technology takes first place among circuit breakers with a high mean time to failure (MTT F) of up to 77,000 years. And no monitoring is necessary! Before it leaves the factory to be integrated in the circuit breaker, the vacuum is placed inside the tube, and after undergoing many tests the quality of the vacuum interrupter is guaranteed: 100 percent reliability until the end of its lifecycle! Vacuum-switching technology is one of the most appropriate technologies for generator switching applications, especially in terms of durability and sustainability.
Generator Circuit Breakers increase the availability of power plants
A generator circuit breaker system (GCB) is the only solution that protects both generator and generator step-up transformer (GSUT) compared with high voltage circuit breakers installed on the high-voltage side. Any circuit breaker installed between a generator and a transformer must be tested according to the dual-logo standard IEC/IEEE 62271-37-13 due to the higher requirements of the generator network. A standard distribution circuit breaker (tested according to IEC 62271-100) isn’t usually suitable for generator protection applications. That’s what Bernd Lenzen from HITACHI ZOSEN INOVA AG explains:
“Depending on the configuration we have to consider a certain selectivity. And here, of course, the generator circuit breaker is an important component.”Bernd Lenzen, Hitachi Zosen Inova AG
More and more peaking power plants – including gas turbine and pumped-storage applications that entail a very large number of switching operations – are looking for a protection solution that keep their operational expenditures to a minimum. That’s where vacuum technology in conjunction with a full-spring drive mechanism can deliver the highest levels of durability and reliability for due to its maintenance free design up to 10,000 switching operations. Our customer Sebastian Gast from VOITH HYDRO GmbH:“We chose Siemens vacuum circuit breaker for the Vianden pumped storage power plant as a result of a lifecycle analysis we conducted together with the end-user. We came to the conclusion- based on the high number of switching operations required to operate the system – that we had a very good solution in terms of maintenance intervals, availability of the system (…)”
The electrical switching cycles exceed by far what is known from SF6 switch in the system. We can switch the rated current very often. Basically, as often as we can switch mechanically. This means that we have no restrictions there.Sebastian Gast, VOITH HYDRO GmbH
For a successful energy transition
In addition to securing power generation assets, the role of a GCB is to synchronize the grid. While moving to a greener energy landscape, the grid infrastructure needs to become resilient enough to integrate renewable energy sources on a large scale. Synchronous condenser plants are growing in importance for grid stabilization. Their rotating mass means that they can provide or absorb reactive power due to the volatile nature of renewable energies. When it comes to providing short-circuit power, the GCB plays a protective role that can handle higher voltages resulting from a temporary larger power infeed. It can effectively synchronize the load, and when a fault occurs it cuts the power to prevent extensive damage inside the transformer.
A reliable and sustainable portfolio
We’ve been innovating in the area of vacuum technology for more than 40 years. The 1950s and ‘60s saw the development of air-blast, minimum-oil circuit breakers and after the SF6 switching technology entered the market. It’s now been about 30 years since the first vacuum circuit breaker was implemented in generator circuit breakers of up to 63 kA with spring-drive mechanisms. Today we’re able to handle up to 110 kA and are slowly phasing out SF6 circuit breakers in this range.
Vacuum circuit breakers now comprise more than 80 percent of the Medium Voltage market – and Siemens offers the world’s first and only vacuum generator circuit breaker (type HB3) for securing and synchronizing power plant applications up to 500 MW. Prof. Heinz H. Schramm at the Technical University of Berlin explains it:
The technology of a vacuum switch is much simpler. We have only one moving contact and one fixed contact, whereas in the SF6 switch, for example, several contacts are parallel. This simple design naturally results in a lower probability of error and thus higher reliability”.Prof. Heinz H. Schramm, Technical University of Berlin
Our entire generator switchgear portfolio features materials that are completely recyclable, require no gas handling, and are part of our sustainable medium voltage“blue portfolio” that protects the climate and complies with environmental standards.
“It is also important for us, especially when planning with the awareness that we should plan responsibly and sustainably for our environment, that the components that are used have a smaller CO2 footprint” Bernd Lenzen, HITACHI ZOSEN INOVA AG.
Reducing gas emissions has becoming a challenge for power plants and industrial applications, and Jean-Louis Drommi who’s responsible for engineering at EDF’s Hydro Engineering Center in France, adds: “the legislations around SF6 are becoming quite tedious and require a lot of time: It requires keeping up to date books, registers on consumption, locations… and therefore beyond the fact of having SF6 and everything it represents, there is this whole administrative phase of management that represents a cost.”
The best alternative to SF6-gas
Regarding the future and the need to reduce our carbon footprint, vacuum technology is considered the viable alternative to SF6-gases “since SF6 happens to be a gas with a potent greenhouse effect, and there are several legislations that are starting to emerge to regulate the use, or even maybe even ban it one day” according to Jean-Louis Drommi. According to the Intergovernmental Panel on Climate Change, SF6 has a global warming potential of around 23,000 times that of CO2 when compared over a 100-year period. It can also form toxic by-products that could pose a health threat to personnel working in the plant if a leak occurred – it is important to forego the use of SF6 gas not only for the environment impact but also for the health of the people handling it.
In pumped storage plants, we always try to keep the number of SF6 equipment low. The effect on the personnel regarding the substances that can escape, including leaks and gas handling, is an argument which is also very present in our company today, which attaches great importance to operational safety.Ulrich Voigt, VATTENFALL Wasserkraft GmbH
To replace existing SF6 circuit breakers, we’ve recently developed a compact and versatile version for retrofit applications in power plants, where space is limited due to existing installations. With its adaptable design and installation, the new HB3-Compact model offers power plant operators optimal flexibility when they’re designing a new plant or replacing outdated equipment. It has a simplified footprint that facilitates the design and dimensioning of the switchgear. The supporting frame design can be customized, and the unit can be mounted horizontally as well as vertically.
Not only has this removed any environmental impact and health and safety concerns caused by the previous, outdated switchgear but the new generator breakers are practically maintenance free, thus reducing costs.
There’s no denying that vacuum switching technology is the best interruption technology in the medium and high voltage levels and generator switching applications for reducing operational expenditures. The impressive MTTF of approximately 77,000 years and the outstanding design and manufacturing process make Siemens GCB “sealed for life.” That’s why we can say that compared with SF6 GCBs, Vacuum GCBs are also more economical. They offer many advantages both technically and commercially: for example, in terms of their lifecycle cost.
The maintenance costs for large SF6 generator circuit breakers are an issue for many operators, based on Voigt’s experience (Vattenfall Wasserkraft GmbH): “Now actually over the many years that the product is used, the OPEX costs play a significant role in the awarding of the contract. We have very good cards here, especially with the product now (…)”
See more at: www.siemens.com/gcb