Lucy Electric

Lucy Electric

Deformation of and stress in the busbars and supports of a medium voltage switchgear during short-circuit current

Problem:

A switchgear must operate safely in an electrical network, where it is exposed to different — sometimes extreme —conditions. A fault downstream of the switchgear can cause a short-circuit current that the switchgear must be able to withstand. Although the duration of this current is short, its magnitude is very high and results in large forces between the conductors. The designer needs to know if these forces can have detrimental effects on the conductors and on their insulating supports. The proper calculation of displacement and stress for a complex conductor arrangement with turns in the current path, touching and sliding surfaces between the conductors and supports, and the dynamic nature of the time-varying load necessitates the use of transient, coupled electromagnetic-structural simulation.

Solution:

The electromagnetic and structural models were generated separately in ANSYS Mechanical. After preparing two geometric models for each of the two fields in a CAD software, we exported them to ANSYS Designmodeler. The base of both arrangements was the same 3D CAD model. In the EM model, we included all the conductors of the current path, but no other solid components, whereas in the structural model we needed only the busbar conductors and their supports. We used ANSYS DesignModeler to prepare the surrounding gas as an “enclosure” in the EM model, and to group volumes in parts where we needed a continuous mesh between the components. We built the structural model and meshed the EM model in the ANSYS Workbench environment. We exported the EM mesh to ANSYS Mechanical APDL, where we set up the proper elements, material properties and boundary conditions. All the parameters of the structural model were set up in Workbench, and the whole model was exported to the APDL environment. An APDL script connected the two models in a single coupled field analysis, added the loads and ran the transient simulation. The goal of this simulation was to calculate the stress occurring in the supports and the busbars.

Business Benefit:

One simulation consisting of approximately 10 time-cycles of the short-circuit current (if resonance does not happen, the highest forces appear within the first cycles) can be run during a night, or if we are interested in exploring a longer duration, it can take around a day (model preparation not included). Within one week, several different arrangements can be analyzed, the weak points identified and the models modified accordingly. This can significantly improve the chances of passing a prototype test and reduce the number of prototypes, saving time and cost in the development process.

Software used: