×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Overcompensation of asynchronous motors

Overcompensation of asynchronous motors

Overcompensation of asynchronous motors

(OP)
Can overcompensation of an asynchronous motor cause its power factor correction capacitor to explode because of the voltage rise?

RE: Overcompensation of asynchronous motors

If you over correct an induction motor when using staic correction, problems can certainly occur. Generally with static correction, the capacitor is controlled by the same contactor as the motor. i.e. the capacitor is effectively permanently connected accross the motor terminals. When the motor is over corrected, the effective resonant frequency of the motor inductance and the correction capacitance is less than the line frequency. During start and run, there is no problem, however when the motor is disconnected from the supply, it acts as a generator, generating voltage at the speed of it's rotation. Initially, (assuming that the motor is at full speed) the output voltage will be at the line frequency and as the motor slows, the frequency will drop. The actual voltage generated is dependant on the residual magnetism in the rotor. While slowing with ovewr correction, the voltage will pass through the resonant frequency of the motor / capacitor combination. At resonance, very high voltages will be generated and damage to the motor and capacitors can result. There will also commonly be very high torque transients that can cause major mechanical damage as well. Correction should only be applied up to 80% of the magnetising current of the motor.

Mark Empson
http://www.lmphotonics.com

RE: Overcompensation of asynchronous motors

To Marke:

I always thought saturation would limit voltage in such a situation. How is it possible to operate an compensated asynchronous machine as generator if resonance between machine and capacitor can lead to destructive overvoltage?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources