Lucy Electric

Melting of canted spring contacts during a high voltage circuit breaker current breaking test

Problem:

The temperature rise of electrical contacts is an essential question during electric switchgear design; the assessment of Joule-heat distribution among contact points is a crucial part of temperature rise calculations. ANSYS solutions provide electrical contact elements to model the additional resistance arising in the infinitesimally thin volume at touching conductor surfaces, but only for static (DC) analyses. When canted spring contacts failed during current breaking tests of a high voltage circuit breaker, Lucy Electric engineers needed to devise an electrical contact modeling method that would work in harmonic and transient simulations.

Solution:

Modeling an electrical contact requires very thin elements, and the existing surface contact element type was not useful in this case. It was not possible to include extremely thin volumes in the geometry, as this led to improper element shapes in the air volume at the edge of the contacts, making meshing practically impossible. Realizing that the change in magnetic field distribution between the contacting surfaces was negligible, Lucy Electric engineers, in cooperation with Hyundai Technologies Hungary, created an APDL macro that split up the mesh at the contact areas, and added nodes and elements with a small thickness to these areas between the conductors. The resistance of the contacts was easily defined by setting the appropriate material properties. Using this unique method, ANSYS simulations showed that contact temperatures reached values that were significantly higher than the melting temperature of both the contact and conductor materials.

Business Benefit:

ANSYS simulations clarified how the electromagnetic effects in time-varying loads influence the current distribution among contact points in circular contact elements. The method developed can be used to assess losses in harmonic analyses, provide input data for steady-state temperature rise calculations, and speed up the design process by reducing the number of failed tests.

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