Current limiting circuit breakers have to be able to restrict the current well before the prospective peak short circuit current is reached. To accomplish this goal it is necessary to open the movable contacts rapidly. The two parameters that have the biggest influence on contact opening are (1) the electromagnetic force generated by the interaction of the current flowing in the movable contact and the self-generated magnetic field of the current leads and (2) the mass moment of inertia of the contact. This paper presents finite element calculations and measurements of the electromagnetic opening force acting on the movable contact of current limiting circuit breakers as well as calculations of the magnetic blow field of the arc. The calculations have been performed for closed contacts as well as for open contacts. The influence of different designs of the current paths leading towards the contact pieces and of the splitter plates, respectively, is shown. Points of emphasis regarding the force calculations are the influence of the shape of the modeled arc and the position of the conducting contact area on the movable contact. Measurements of the opening force have been performed for currents up to several kA. They show a satisfactory agreement with calculations. A current path that encloses the movable contact in a coil-like turn generates-the highest opening force on the contacts.
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