1 EE – 3410 Electric Power Fall 2003

An operation of any electromechanical device, in that number electric machines, it is electric motors and generators, can be seen as: a) An impact of magnetic field on a piece of ferromagnetic material, b) An interaction of two magnetic fields: magnetic field of primary part and magnetic field of secondary part; the secondary magnetic field can be generated: either by a current flowing in a winding (conductor), or by permanent magnet. The machines that belong to the group (a) are called the reluctance motors, and the machines that operates on the basis of the mode (b) are the rest of the majority of electric machines, it is generators and motors. We will discuss these various electric machines starting with our very first experience with permanent magnets. In electric machines the basic requirement for the primary magnetic field is: it has to be in motion. It can move with: translation motion – we call it a magnetic travelling field, which exists in linear machines rotary motion – a rotating magnetic field, which is in rotating machines complex motion described by two or three space co-ordinates, which is generated in electric motors with two degrees of mechanical freedom, e.g.: • rotary-linear motors with helical motion of the rotor, • motors with spherical rotor • X-Y linear motors. In the following sections we will concentrate on the linear machines. The rotating machines will be seen as a geometrical conversion of the flat linear structure into the cylindrical or disc structure.