A rotary electric machine

A rotary electric machine of alternating current type designed to be connnected directly to a distribution or transmission network comprises at least one electric winding. The winding comprises at least one electric conductor, a first layer with semiconducting properties surrounding the conductor, a solid insulating layer surrounding the first layer and a second layer with semiconducting properties surrounding the insulating layer. A brushless excitation system, switchable between positive and negative excitation, is also arranged for excitation of the machine. An electric power plant comprises such a rotary electric machine. In a method of exciting a rotary electric machine with both positive and negative excitation current direction, a two-way field over-voltage protection means (8, 10, 12, 14) or a two-way discharge circuit is connected temporarily across the field winding (4) of the machine.