Etzel substation ready for operation

After a one-year construction period, the new Etzel substation will be inaugurated in Altendorf (Canton of Schwyz) today in the presence of public officials. Axpo and the Electricity Utilities of the Canton of Zurich (EKZ) invested a total of CHF 8 million in the new facility that will reinforce power supply in the Höfe and March districts: For the first time worldwide, the new, climate-friendly insulation gas g³ will be used in this high-voltage substation.

We asked Christian Lindner, Head of Engineering Grids Division, what's behind the chemical formula g³ and SF₆ and why insulation gas is used in substations.

Where and for what purpose are insulation gases used in substations?
Insulation gas is used in switchgear to insulate important components such as contacts and conductors. The 100-kilovolt high-voltage switchgear like at the Etzel substation must have a sufficient gap between the electrified and non-electrified parts in order to prevent a voltage flashover. This can lead to a short circuit and endanger human lives as well as the security of supply. Insulation gas can reduce the gap between components to just a few centimetres. In outdoor substations the air takes over the insulation function. The distance between electrified components has to be at least one metre in these installations.

Insulation gases enable the compact construction of substations in an encapsulated form. In contrast to outdoor substations, gas-insulated switchgear require much less space and can be built in residential areas.

What sort of gases are SF₆ and g³? Are they dangerous? What are the differences between the two?
SF₆ stands for sulphur hexafluoride and has been in use as a switch and insulation gas in high-voltage technology worldwide for about 50 years. The gas is non-poisonous per se, and unproblematic as long is in remains enclosed in the encapsulated system. If gas escapes through leakage, it develops its greenhouse gas effect and promotes climate warming. It is therefore crucial in operation to keep losses as low as possible independent of the type of insulation gas. In an international comparison, Axpo has the lowest loss rate for SF₆ with only 0.2% per year thanks to the safe operation, careful controlling and maintenance of its plants. The international benchmark is 0.5%.

g³ stands for green gas for grid and is a new climate-friendly gas mixture developed by General Electric GE and 3M. It has only been available since 2015. The gas was used for the first time worldwide in a pilot project launched by the British grid operator National Grid. The greenhouse gas potential of this alternative gas is 98% lower than that of SF₆. g³ is non-poisonous, non-combustible, with marginal impacts on the climate thanks to its low warming potential. Worldwide the utilisation of g³ as an alternative to SF₆ in a high-voltage substation is a premier. 

Utilisation of the new, ecologically efficient gas g³ at the new Etzel substation and Axpo's low loss rate is a double benefit to the climate. 

What was tested and what were the criteria for using g³?
In the tests, various malfunctions were simulated, e.g. a short circuit or a manual operation error. Human safety and security of supply must be ensured at all times. All the tests with the gas that were carried out by General Electric according to international IEC norms produced positive results. We are pleased that we can now use this ecologically efficient gas in the new substation and take on a pioneering role with our project partner EKZ.

Will Axpo use this climate-friendly gas in all its gas-insulated substations?
Climate-friendly gases such as g³ will, if possible, be used in new power grid projects. The search for innovative solutions to continually reduce greenhouse gas emissions in all their business activities is an element of the Axpo and EKZ sustainability strategies.

The insulation gas in existing substations or switchgear cannot simply be exchanged. This has two reasons: Firstly, g³ cannot be used in all high-voltage switchgear, i.e. the system has to be completely redesigned or replaced. Secondly, the ecologically efficient gas g³ can currently only be used in systems with maximum 110 kV. The focus in existing systems is on maintaining the record-low loss rates for gas leakage in order to keep climate impacts as low as possible.