ABB (IT)

RCD Tripping Mechanism

The objective of this test case is to replace 2-3 pieces of an existing RCD device mechanism with a single flexible part.

The compliant mechanism must, of course, replicate the same nominal static and dynamic behaviour of the corresponding rigid system. As regards this RCD benchmark, three different operations must be accomplished by the mechanism:
- arming
- tripping and automatic re-arming with free lever
- tripping with locked lever

Tripping operations are started by an external force coming from a relay. This force is very low compared to the other forces acting inside the mechanism.
The time needed to perform tripping operations is also an issue that must be precisely replicated.
 

Shunt Trip Device Lever

A Shunt Trip Device is an electrical apparatus used to activate a circuit breaker if the voltage level drops under a stated value. The actual mechanism used within the device contains a locking lever able to rotate around a fixed pin and having a preloaded rotational spring acting on it. In the long lasting equilibrium position, the lever is kept in a fixed position by the preloaded spring and a rotational locking. During the mechanism operation, the lever is rotated by an external torque and the torsional load on the spring increases. When the external force disappears, the spring pushes back the lever into the original equilibrium position. The proposed compliant solution basically replaces the spring by adding a flexible appendix to the lever (see next figures).
The design of the solution starts from two different loaded conditions, both of them having a deformed configuration and a predefined torsional load. The unknown in this case is the undeformed solution that in principle can be found using an inverse deformation approach.

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Last modified, May 2006