Motor speed control is important in many applications. It allows for precise control of the application. This allows the same equipment to be used for multiple products or processes.

Motor speed control is important in many applications. It allows for precise control of the application. This allows the same equipment to be used for multiple products or processes.

Stamping Machine – pressure exerted by the stamping head.

Cooling Tower – temperature of the cooling source, such as water.

Polishing Machine – speed of the rotating polishing head.

Commercial Bakery – speed at which conveyors move a batch through the oven.

As you may recall from Module 16, Fundamentals of Motors and Motor Control, all AC motors have a synchronous speed. This is the speed at which the motor is designed to run.

Suppose you have a motor connected to a conveyor belt application, and you want to slow the conveyor speed. What can you do? The motor is built to run at only one speed. The answer is you find a way to change the motor’s speed.

Many methods for controlling the speed of a motor are in use today. The list that follows is neither detailed nor complete, but will serve to give you an idea of the variety of methods available.

Electrical Methods – The motor speed is actually changed electrically.

Adjustable Voltage – changing the DC input voltage changes the DC motor’s speed.

Adjustable Frequency – changing the input frequency changes the AC motor’s speed.

Eddy Current – changing the strength of the magnetic field changes the AC motor’s speed.

Mechanical Methods – The motor speed stays constant , and is converted to the desired speed, using gears, sheaves, clutches or other mechanical means.