Cost-effective Rotational Switch for SF6-free Gas Insulated Switchgears

Medium Voltage (MV) gas-insulated switchgear (GIS) are key components in primary and secondary distribution networks. ABB Electrification Norway in Skien manufactures 12, 24 and 36 kV gas insulated switchgears for the world market. These medium voltage (MV) apparatus have traditionally been based on sulphur hexafluoride (SF6) gas as the electrical insulation and current interruption medium. Because SF6 is an extremely strong greenhouse gas, significant efforts have been made to develop SF6-free switchgears to reduce the use of greenhouse gases. ABB is currently developing SF6-free switchgear technology up to 24 kV, air and mixtures of air and C5-fluoroketone referred to by the trade name AirPlus TM are used instead of SF6. In this project, we aim to develop a new "three-position switch concept" for the ratings 12, 24 and 36 kV, using air or AirPlus TM in order to meet market demands and complete the SF6- free portfolio. The project is a collaboration between NTNU, SINTEF, KTH and ABB. A successful outcome of the proposed project will pave the way to replace SF6 also for the higher voltage level and enable reductions in manufacturing costs. Since September 2020, PhD student Paul Monceyron Røren has started his scientific project in NTNU. A PhD start-up meeting was held together with ABB and the short-term targets were defined. The test setup is finalized to investigate the breaking performance of different ablating material. A set of experiment have conducted for different materials in Air and further tests are planned to be conducted in AirPlus in near future. A master student joined the project and is doing his thesis on load break switching using polymer ablation. SINTEF has designed and finalized building a new test bench for performing interruption experiments in air and AirPlus? using test switches and prototypes with rotational movement. The setup is enabling usage of a simple knife contact, in a three position configuration. However, since it comprises several new ideas it is still many issues to investigate and develop further. This prototype has promising characteristics for eventually ending up as a new product for ABB. ABB has performed several development tests to explore suitable parameters for switches improving the breaking performance and a new product is under development.

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ABB ELDS in Skien manufactures 12-40.5 kV compact, gas insulated switchgears for the world market. Traditionally, these have been based on using sulphur hexafluoride (SF6) gas as the electrical insulation- and current interruption medium. Since SF6 is an extremely strong greenhouse gas, ABB is currently working on replacing this gas with an environmentally benign alternative; a mixture of air and fluoroketone referred to by the trade name AirPlusTM. The manufacturing costs for the AirPlus™ switchgear are – due to the poorer insulation and interrupting capabilities compared to SF6 – not as low as for the SF6-based solution. The SF6 switchgear has a so-called "three-position switch", which can take "closed", "open" and "earthed" (grounded) positions, with using only one operating shaft. For the existing AirPlus™ switchgear, the load current switching function and the earthing function are performed by two separate devices. This solution takes up more space and materials, and even more important, makes up a considerably portion of the switchgear manufacturing costs. The proposed project aims at developing a compact and inexpensive "three-position switch" concept for air and AirPlus™, based on a rotational movement and preferable with a simple "knife contact" system, instead of the linear movement, axisymmetric "tulip-pin" contact device currently applied in the AirPlus™ switchgear. This involves developing and testing design features (piston/cylinder arrangements, nozzle geometries, evaporating polymers, etc.) that provide a rapid contact movement together with a sufficiently strong gas flow onto the switching arc to extinguish it and thereby interrupt the current. The project is a collaboration between ABB ELDS in Skien, SINTEF, NTNU and KTH.