3. Special effects

3.1 End effects

In a rotary motor, induction is distributed in the form of a rotating wave which, at the scale of the pole pitch, has no preferred value anywhere in the air gap.

This is no longer the case in linear motors, where induction can only be represented very approximately by a sliding wave; it varies not only in phase, but also in modulus, at many points of the air gap, because it is disturbed by end effects, which we will classify into two categories:

• the finite-length effect, due mainly to magnetic discontinuities at the machine inlet and outlet;

• the finite width or edge effect, due to the closing of currents inside the active part of the armature.

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