# Initialization by FE solution: particularities

## Starting a Transient Magnetic application on the basis of an AC Steady-State solution

In the case of a Transient Magnetic application starting on the basis of an AC Steady-State solution, it is necessary to carefully choose the phase when exporting the AC Steady-State FE solution in the .FTS file, in order to replicate the same conditions.

Remember: *
• AC Steady-State Magnetic application: the sources (voltage or current) are considered as cosine functions when transformed into the phasors used for solving.

• Transient Magnetic application: the sources (voltage or current) being mainly defined with a sine function, the phase must be set at φ = 90° when creating the .FTS file in the AC-Steady-State magnetic project. On the other hand, if the Transient Magnetic sources are defined with a cosine function, the phase must be set at φ = 0° when creating the .FTS file.

It is also important to note that if the Transient Magnetic project includes magnets, these being prohibited in the AC Steady-State application (and therefore replaced by air), the results obtained in the Transient Magnetic project will be erroneous due to a dPhi /dt (with Phi the magnetic flux of the magnet and dt the time increment from one step to another) more or less important depending on the nature of the project (rotating machine, actuator...) because of the time rate of the magnetic flux. Indeed the magnet being absent at the first time step (t=0) because initialized with an AC Steady-State project and reappearing at the second time step during the Magnetic-Transient project (end of the initialization by file), the results may be altered.

Similarly, the projects must be strictly identical (project creating the initialization file and transient project) from different points of view:
• geometrical (same dimensions);
• mesh;
• physical (same materials used by the same regions, mechanical sets ...);
• and the electrical circuit (same components, name of the components ...).

Also, in the circuit, when Flux performs an initialization with a finite element solution, it solves an initial circuit in which the initial values ​​are determined by the solution that was used to create the file for the finite element solution initialization. In this circuit, the coil conductors type components have initial current and thus at t=0 they are considered as current sources. The initialization of the other circuit components follows the common rules of circuit analysis, i.e. a capacitor is an open circuit, an inductor is a short circuit, etc. In this context, a high value resistor in parallel with a coil conductor component used to measure the voltage at the coil terminals leads to a problem when the initial circuit is solved. The initial current of the coil conductor component is forced to pass through this high value resistor generating a high voltage. This voltage is considered in the next step of the time resolution producing a false transient response.

## Starting a Transient Magnetic application on the basis of a Transient Magnetic solution

In the case of a Transient Magnetic application starting on the basis of a Transient Magnetic solution, it is necessary to take certain precautions with the cinematic coupling and/or with the circuit coupling.

• Cinematic coupling: at the moment of export of the FE solution:
• Note the value of the speed and of the position of the mechanical set in motion (translation or rotation)
• Introduce these values in the Flux project 2 (initial values of the mechanical set in motion)
• Circuit coupling: if the current/voltage source is described by means of a time formula, in the Flux project 2, move back in time the current/voltage source.