Voltage which produces eddy current
I would like to estimate the voltage which induces the eddy currents.

Suppose the total flux through the core of the transformer is given by some function of time \$\Phi(t)\$. Suppose there are N equally sized laminations in the core. We can call the flux through any single lamination \$\phi(t)\$. Assuming that the flux is evenly distributed through the laminations,
$$\phi(t) = \frac{\Phi(t)}{N}$$
There current in a lamination will not be uniform, but will depend upon the loop for that current, and the amount of (changing) flux linked by that loop. The loop with the largest amount of linked flux will be the loop that follows the surface of the lamination. That loop will link all the flux in the lamination.
The emf of that loop will simply be
$$ V = -\frac{d\phi}{dt}$$
The average emf of the current loops in a lamination will obviously be lower.