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, in which air and air mixtures are used instead of SF6. In this project, we aimed to develop a new "three-position switch concept" for the ratings 12, 24 and 36 kV, using air or air mixtures 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 could pave the way to replace SF6 also for the higher voltage level and enable reductions in manufacturing costs. The PhD student Paul M. Røren joined the project on the first of September 2020. A test setup to test the effects of current interruption on the SF6 alternative AirPlusTM was build and continuously improved throughout the project. Using this setup, experiments at multiple filling pressures and current levels were performed for air and AirPlusTM, where the arc current, arc voltage, post-arc current, travel curve of the switch, and pressure could be measured. In addition, a high-speed camera could be used to film the arc through an in-house build quartz window. Many experiments have been performed and some of the results have been published. Sintef has finalized several test benches for performing interruption experiments. During the development work, several design alternatives, with gradually improved characteristic, has been evaluated and tested. ABB has started a full-scale product development activity bases on the best design. Dielectric and fluid flow simulation have been used to optimize the proposed design. ABB has performed several development tests to explore suitable parameters for switches improving the breaking performance and a new product is under development.

The technology platform developed in this and parallel projects can be implemented in other, future products of ABB Skien and also in product from other ABB companies. ABB Skien is the Lead Technology Centre for developing the coming generations of compact MV switchgear globally. To maintain this position, it is crucial to stay in the research forefront, and have a close and good relationship with universities and research institutions active in these field. Today ABB's MV switchgear plants in Skien, China and India combined use approximately 100 000 kg SF6 per year. When ABB eventually has developed a full range SF6-free product portfolio, a significant amount of this strong greenhouse gas will be taken out of circulation and use. As a result of the finding in this project ,ABB has now a good position for developing a environmental friendly product line within the coming years. For NTNU and SINTEF Energy Research the project strengthens their long-term relationship with a Norwegian-based manufacturer of power equipment. It also educates young PhD candidates in a topic important for making the energy sector more sustainable.

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.