Generally in all industrial process it is desired that in beginning the motor should be run at slow speed and then gradually increased to meet the rated speed. By using various methods the speed of a motor can be controlled which gives various speed in wide range for various system. Earlier the conventional method s of speed control were used which gave limited range of speed. Now the new technology is used in which solid state devices are used to control the speed and it giver very wide range of speed control. Due to their manifold advantages such as compactness fast response more efficiency more control capabilities less cost etc, SCR controlled schemes have totally dominated the conventional methods o f speed control.
The electric are classified based on the nature of the electric supply accordingly the electric motors are basically classified as: