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Lorentz Forces in Switches and Contacts

A disconnecting switch is a mechanical switching device that is normally closed, capable of carrying currents as well as opening or closing a circuit. Disconnecting switches are not meant to open live circuits but, rather, to disconnect apparatuses at the instant when they do not carry current. However, in large electric power systems operating at high voltages, disconnecting switches are sometimes forced open due to the magnetic repulsion caused by high short-circuit currents, which is not desirable. Determining this magnetic force helps designers to design switches that can withstand this force; in addition, it helps in creating circuits that produce the least force on the switches. Heavy-duty switches come with additional latches to withstand the force exerted on them and to keep them closed.

An area of concern for most electrical engineers who work with disconnectors and contacts is determining the electromagnetic force that sometimes causes them to open undesirably. ANSYS Maxwell software helps in calculating this force, allowing engineers to design switches that withstand the force. Further, parametric study can be conducted to evaluate the influence of design variables, such as thickness of a switch or current through contact on the electromagnetic force. The results obtained from Maxwell agree well
with the published textbook results by H.B. Dwight and P. G. Slade.