Circuit Breaker - Single Phase AC | SystemVision® Cloud

Mike DonnellyDesigner

Mike Donnelly

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Original member of the SystemVision development team. Modeling and Applications Specialist

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Description

This is a physical or “assembly” model of an electro-magnetic circuit breaker. Rather that modeling the pure electrical “behavior” of that type of circuit protection device, this model represents the actual assembly of physical components which could be used to construct a real circuit breaker. The components are multi-discipline, including electrical, magnetic and mechanical natures. The color coding of the connections among them makes it easy to see these various aspects and their interactions.The section with black connections represents the electrical aspect. The voltage source is the AC line-in voltage, and it is applied across a switch and winding element which are part of the circuit breaker. The switch represents the make/break function of the contactors. A fixed 8 Ohm load resistor is attached to this protected part of the circuit, as well as a switched additional 8 Ohm load in parallel.The section with purple connections represents the magnetic aspect of the breaker. The winding current produces an MMF in proportion to the number of turns, and this MMF drives flux around the magnetic loop. The Neodymium-Iron-Boron permanent magnet also drives flux around the loop, but in one direction only. The magnetic core model represents the flux path through the iron, and the air-gap model represents the energy conversion between the magnetic and mechanical domains.The section with orange connections represents the mechanical (translational) aspects, including a hard-stop which limits the travel of the moving armature, a preload spring, plus the viscous drag and mass of the armature. A simple “glue” model was created to convert the armature displacement into a logical control signal that opens the breaker switch to interrupt the load current, when the air-gap exceeds the contactor over-travel length. The user’s ability to easily create a new custom VHDL-AMS model, when the needed function doesn’t already exist, has value which cannot be overstated.The circuit breaker functions when the current in the winding is of the right polarity and magnitude to create an MMF that sufficiently cancels the MMF of the permanent magnet. This causes a flux drop across the air-gap, to the point where the magnetic attraction force can no longer overcome the pre-load return force of the spring. The armature is then rapidly pushed away. In the simulation results, note that the additional load is applied at 60 msec. The current in the winding increases to just over 40A (peak), and the air-gap force drops below 8N, at which time the armature begins to pull away, opening the electrical circuit. The armature bounces as it reaches the stiff travel limit.This model can be used to re-size or select alternate components (e.g. try a spring with different stiffness or a different magnetic material). It can also be used to assess margins on the current trip level (e.g. try a 10 Ohm resistor for the “additional” load, the breaker won’t trip!), or the opening speed or other performance aspects. This type of “assembly” model is also suitable for exploration of new design concepts.

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Comments

Submitted by Ramiro on Sun, 05/01/2016 - 13:49

This design was really useful because i was having trouble understanding how to build an interaction between magnetic, mechanical and electrical elements. This examples show it all!

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Mike DonnellyDesigner

Mike Donnelly

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Thanks for trying out SystemVision.com

Mike DonnellyDesigner

Mike Donnelly

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