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Coil Electromotive Force

This scalar field gives the local density of the induced voltage in an excitation coil:

\[ e = \frac{\partial \mathbf{A}}{\partial t} \cdot \boldsymbol{\tau}, \]

where:

  • \(e\) is the electromotive force density (V/m³).
  • \(\mathbf{A}\) is the magnetic vector potential (Wb/m). Its time derivative has the unit V/m.
  • \(\boldsymbol{\tau}\) is the unit current density of the coil (1/m²). It contains the number of turns and the reverse_direction sign.

Registered name: "Coil Electromotive Force".

The volume integral of \(e\) over the coil volume \(\Omega_c\) gives the back-EMF of the coil (V):

\[ \mathcal{EMF} = \int_{\Omega_c} e \, d\Omega. \]

The Back-EMF Report calculates this integral for you.

This coefficient is available only with the Time-Domain Magnetic model.

Typical use

  • Show where in the winding the voltage is induced. For example, find the coil sides that see the largest flux change in a motor slot or at a transformer core window.
  • Examine solid conductors, such as bus-bars under a current pulse, where the induced voltage is not uniform over the cross-section.

Example

Export the field with the field exporter:

field_exporter = sim.get_field_exporter()
field_exporter.add_field_output("Coil Electromotive Force")