# How to calculate speed voltage from Maxwell's laws

## Main Question or Discussion Point

Hi,

In classical induction machine analysis, the induced voltage (or curl of the electric field) is equal to the time rate of change of the magnetic field (B) plus the 'speed voltage'. This is understood very easily from electrical circuit models of the machine.

However, going purely from Maxwell's equations (1. div(E) = rho/epsilon; 2. div(B) = 0; 3. curl(E) = -dB/dt; 4. Curl(B) = mu(J + epsilon*dE/dt) ) how can one arrive at the same observation as above?

Thanks
e.

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jtbell
Mentor
What is "speed voltage"? I don't remember ever seeing that term before, in American English. Perhaps there is a language-translation problem?

Hi Jtbell,
Thanks for your response. I was reading a book on linear induction motors, and therein it was written:

$\frac{de}{dx}$=$\frac{db}{dt}$ + v$\frac{db}{dx}$

The first term is referred to as a transformer voltage, and the second, a speed voltage. I want to know how to get this from Maxwell's laws. I recently read something about reference frames; I think my answer lies in that direction.

Best
e.