“Electrical machines are used by most industries to generate power and/or drive process equipment. Motors convert electrical energy into mechanical energy and generators perform the opposite functions. The distribution of electrical power is clean and efficient and is easy to control. Motors and generators convert energy from one form to another through the action of a magnetic field. Power can be placed at a precise source without a large investment in infrastructure. Electrical power like mechanical power is not easy to store. However, due to the existence of large grids, common usage, and standardization in supply, it is readily available and does not need to be stored. Commonly used electrical machines include generators, AC induction motors, DC motors, wound rotor motors, and synchronous motors.

"Electromagnetic Principles:

Electrical machines convert energy to one form or another through the action of magnetic fields. Electrical current, measured in amperes, is induced in a conductor by an electromotive force, measured in volts. The current flow is inhibited by resistance, measured in Ohms. The measure of the strength of a magnetic field at a given point is called the flux density — lines of force per unit of cross-sectional area. 

The total flux is then the flux density multiplied by the area and the cosine of the angle between the direction of the flux and a line drawn perpendicular to the plane of the area.

Electromagnetic fields are generated by currents passing through wire coils. If a coil of wire is wound on an iron (ferromagnetic material) bar as shown in Figure 1 and a current is passed through the coil, flux will be present in and around the coil. The ability of an electric circuit to produce magnetic flux is known as its magnetomotive force, mmf. The measure of mmf is the work done in moving a unit pole through any path taken by magnetic lines of force and back to the starting point, against the magnetic force produced by the current. The magnetic force produced by the current is proportional to the number of turns on the coil and to the current and therefore has units of ampere turn. Then the total flux is equal to the mmf divided by the reluctance of the magnetic circuit.

When a wire carrying a current is placed at right angle to a magnetic field, a force will be generated that moves it out of the field (Figure 2). The direction of the force will depend on the direction of the current in the wire and on the polarity of the field.”