CST – Computer Simulation Technology

Low Frequency Simulation of a Gas Insulated Switchgear

CST EM STUDIO® (CST EMS) can be applied to the simulation of an ABB Calor Emag SF6 Gas Insulated Switchgear (GIS) such as the one depicted in figure 1 which was also simulated in [1]. A primary goal of such a simulation is to obtain the current distribution in the switchgear conductors with proximity and skin depth effects taken into account. The CST EMS Low Frequency solver is appropriate for this purpose. The geometry is imported from Pro/E® and consists of a metallic housing in which a three-phase conductor system is situated. The metallic housing is considered as perfectly conducting whereas the inner conductors have a electrical conductivity of 3.2e7 S/m. 50 Hz three phase currents of magnitude 4000 A, shifted in phase by 120 degrees, are injected via 3 so-called current paths, defined at the ends of the conductors on the same side of the GIS....



Figure 1: Gas insulated switchgear with housing, conductors and current path excitation arrangement

The skin depth must be taken into account when meshing the model hence a large number of mesh cells are required. This model, solved with the CST EMS Low Frequency (magnetoquasistatic) tetrahedral solver, consists of 1.48 million tetrahedrons corresponding to 1.72 million complex unknowns and simulates to an accuracy of 1e-6 in just 8 minutes on an Intel 2 GHz Woodcrest system.



Figure 2: Tetrahedral mesh used for the simulation of the gas insulated switchgear

The generated mesh and the current path excitations for the simulation are shown in figure 2. The conductors have been adequately discretized to allow for the correct modeling of the skin depth by specifying a maximum mesh step width.



Figure 3: Phase variation of current distribution in the conductors

Further post-processing quantities such as the electrical losses and forces on the conductors may also be calculated. This article has demonstrated some of the powerful capabilities of CST EMS for the simulation of a medium voltage switchgear component, namely, the comprehensive CAD Import features and the fast and efficient low frequency solver.

References

[1] Oliver Sterz, Andreas Hauser, Gabriel Wittum, "Adaptive Local Multigrid Methods for Solving Time-Harmonic Eddy-Current Problems", IEEE Transactions on Magnetics, Vol. 42, No. 2, February 2006.

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