Power & Control Devices

The control of electrical power is one of the four main aspects of industrial automation. Its function is to switch electrical energy to power devices when required to do so, according to instructions coming from an automatic control system. These instructions are the result of the control system processing input signals from automatic pilot devices (sensors, limit switches, etc.) and from manual devices such as push-buttons, etc. (man-machine dialogue components) The most common type of power device requiring control is the asynchronous squirrel cage motor and these are widely used to provide motive power for industrial machinery. Such motors are usually controlled by motor starters, which provide the functions of isolation, power switching and motor overload protection, and these fall into three main categories : 1) Starters that provide On or Off control, whereby the motor will start, accelerate and then run under nominal conditions according to its own characteristics. 2) Electronic “soft-starters”, whereby the motor will start, accelerate and decelerate under the precise control of the starter, but at full speed will run according to its own natural characteristics. 3) Electronic “variable speed drives”, whereby the motors starting, acceleration, running speed and deceleration will all be under precise control of the drive.