The electric motor is a machine capable of converting electrical energy into mechanical energy. The induction motor is the most widely used type of motor, because it combines all the advantages offered by the electrical energy such as low cost, easy of supply and distribution, clean handling and simple controls - together with those of simple construction and its great versatility to be adapted to wide ranges of loads and improved efficiencies. The most common types of electric motors are:
A ) DIRECT CURRENT MOTORS
These motors are quite expensive requiring a direct current source or a converting device to convert normal alternating current into direct current. They are capable of operating with adjustable speeds over a wide range and are perfectly suited for accurate and flexible speed control. Therefore, their use is restricted to special applications where these requirements compensate the much higher installation and maintenance costs.
B ) ALTERNATING CURRENT MOTORS
These are the most frequently used motors because electrical power is normally supplied as alternating current. The most common types are:
1) SYNCHRONOUS MOTORS:
synchronous motors are three-phase AC motors which run at fixed speed, without slip, and are generally applied for large outputs ( due to their relatively high costs in smaller frame sizes ).
2) INDUCTION MOTOR:
these motors generally run at a constant speed which changes slightly when mechanical loads are applied to the motor shaft. Due to its simplicity, robustness and low cost, this type of motor is the most widely used and, in practical terms, is quite suitable for almost all types of machines. Currently it is possible to control the speed of induction motors by frequency inverters.
