In ElMag, or the “ElectroMagnetics” tab, users define electric connections between winding groups, turns, and sources. All coil geometries, including individual turns if they have their own geometry, are represented as electric components and connected to other components using circuits.
The workflow to set up the electromagnetic connections is as follows:
- Enable Secondary Windings if needed (typically, none for inductors and 1-2 for transformers)
- Specify the Excitation type of sources connected to the windings, such as current, voltage, or circuit (only for secondary).
- Set the Connection type between different coil groups
- Add Additional Coils (e.g., when connecting the inductor to the transformer)
- Select the Winding type (primary, secondary, 2nd secondary, additional coil)
- Set the Connection type between individual turns within a group
- Switch to Terminals selection and make any necessary changes to winding terminals.
Winding and excitation configuration for electromagnetic simulation of hybrid transformer and inductor
Excitation
TRAFOLO connects voltage or current sources to windings using circuits. Under the Excitation section, you select the type of source. For secondary windings, you can also connect them to the load using the Circuits functionality.
We recommend using currents for excitation whenever possible. You can read our article about the role of current in calculating core losses in transient simulations. In brief, currents in transformers uniquely define the magnetizing current and magnetic field. The current or impedance must be set on the secondary side if the primary winding is connected to a voltage source.
You can modify the connections between sources and windings in the next Circuits tab. For example, in 3-phase cases, windings are connected in a star configuration by default, which can be changed to a delta configuration by rearranging the connections.
IMPORTANT: It is impossible to set up both current and voltage simultaneously.
Connection
This defines connections between winding and coil geometries.
There are two connection levels – within a coil group if it consists of multiple geometries, e.g., individual wires, and on a winding level when we combine multiple coil geometries into one winding.
Coil group connection type – defines the connection on a higher level – between coil groups:
- Series: Results in identical current among all coils.
- Parallel: Results in equal voltage among all coils, with the current being split.
Connection – defines the connection on a lower level – inside coil groups on a turn/strand level:
- Series: Results in identical current across all geometries.
- Parallel: Results in equal voltage across all geometries.
Terminals
One of the most common mistakes in transformer setups is not accounting for the current directions in the primary and secondary windings. In simplified transformer models, primary and secondary windings currents flow in opposite directions. The net ampere-turns (the difference between turns times current for the primary and secondary) form the magnetizing current and magnetic field, determining the losses.
If the primary and secondary windings carry the same ampere-turns but in opposite directions, the magnetic flux in the core cancels out, resulting in zero hysteresis losses.
In the terminal preview, you can set terminals to Positive, Negative, or Undefined, where Undefined ignores the terminal by setting no current flow.
IMPORTANT: Each geometry should have at least one positive and one negative terminal. Since
Terminal setup for electromagnetic simulation of hybrid transformer and inductor
You can also set multiple positive or negative terminals. In this case, the solver will apply the same voltage to all terminals of the same type while splitting the current among them.
TRAFOLO requires windings/conductors to have at least one positive and one negative terminal.
