Magnetic circuits

The conversion of electrical energy into mechanical energy or electrical energy of different voltages (transformers) involves two types of phenomena:

• electrical phenomena associated with current ;

• magnetic phenomena associated with magnetic flux.

These two types of phenomena, linked by Maxwell's equations, interact very directly in electromechanical and electromagnetic systems. Indeed, the corresponding circuits, the respective carriers of current and flux, are always intertwined.

The study of any electromechanical system can be linked to two models at different levels.

The Maxwell model , characterized by local equations, assumes continuous media. It is mainly used to analyze the distribution of field lines (magnetic induction, current density) associated with an electrical or magnetic medium.

Kirchhoff's model, characterized by the notion of circuits, comprising components (resistance R, inductance L and capacitor C) and quantities (voltage U, current I and magnetic flux Φ), results from the integral of fields or local variables.

The use of such a model and associated equations, where possible, simplifies the analysis and increases its efficiency.

The analysis of magnetic circuits mainly involves moving from Maxwell's model to Kirchhoff's. This is done by taking into account the properties of magnetic phenomena, based mainly on flux conservation and the permeability of the various media. This is done by taking into account the properties of magnetic phenomena, based mainly on flux conservation and the permeability of the various media; furthermore, the analogy with electrical circuits enables a better understanding of the phenomena.

Mastery of magnetic circuits, in local or integral form, enables us to process permanent magnets and ferromagnetic circuits, in order to calculate the resulting forces and torques, as well as parasitic effects such as saturation.

Finally, the design of systems using magnetic circuits illustrates, through examples, the specific approach.

The basic principles of electromagnetism in the stationary (low-frequency) domain, and the magnetic circuit methodology derived from them, are the subject of this dossier. Application examples are presented in document