Remote transmission of mechanical energy would certainly be a dream two centuries ago. Nowadays we live with it and we may not even realize that we use mechanical energy wherever we want, but that it was actually produced hundreds, if not thousands of miles away. The transmission of mechanical energy from places where it is available to places where it is necessary, is nowadays achieved by means of machines that transform mechanical energy into electrical and electrical into mechanical energy. Electromagnetism plays a fundamental role in the conversion of energy and their understanding is important to have a complete mastery of the subject. The magnetic field that involves the operation of the electric machines can be originated in permanen...