Jump to content

Variable Speed Drives


Recommended Posts



Welcome to the forum.


The induction motor is a pseudo synchronous device, that is it tries to run at the speed of the supply. If you reduce the voltage to the motor, you will increase the slip for an given load and this will cause the motor to slow, and increase the losses in the motor. There is a slip where maximum torque is developed and below this speed, the motor will stall.

In most induction motors, this maximum torque speed is close to full speed so the speed control that can be achieved by variable voltage is very small. Additionally, if the load on the motor is high, reducing the voltage will increase the current and damage the motor.


There are some motor designs that use a high resistance rotor. These can operate at slips of up to 100% and these can be controlled by a variable voltage. These are not standard induction motors, but are typically special motors designed into fan assemblies.


The only way to control the speed of a standard induction motor, is to use a VFD which controlls both frequency and voltage.


Best regards,

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Create New...