×
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

Motor power factor assumptions

Motor power factor assumptions

Motor power factor assumptions

(OP)
I need to assume a power factor for a 4160V motor and for a 600V motor - what are acceptable values?

RE: Motor power factor assumptions

PF 0.8 at full load is commonly used. It is a fair guess for most normal motors and it also makes the math very simple since 0.8^2 + 0.6^2 = 1. Hence magnetizing current is 60 percent when "torque" current is 80 percent of rated current. And that does not mean that total current is 140 percent  

RE: Motor power factor assumptions

Hello RegDunlop

If you are about to apply static power factor corection, do not apply it based on an assumption. You must be very careful not to correct to more that 80% of the magnetising current if you are permanently connecting the capacitors to the motor circuit and using the same starter to control both.

For bulk correction and voltage drop calculations, then the assumption is fine.

The power factor can vary considerabley depending on the size and speed of the induction motor.
Larger motors tend to have a much lower magnetising current (down to 20%) than small motors (up to 60%). Two pole motors have a lower magnetising current than 8 pole motors and submersible pump motors tend to have a high magnetising current.

Best regards,

Mark Empson
http://www.lmphotonics.com

RE: Motor power factor assumptions

Just to add to skogsgurra's good response, voltage doesn't matter.  What might matter is whether the motor is synchronous or induction.  0.8 is a good number for induction motors at reasonable loads.  With synchronous motors, it's usually a controllable factor.

Best to ya,

Old Dave

RE: Motor power factor assumptions

For actual induction motor manufactures, consider the following guidelines:

4160 Volts is used for large motors, 300 HP and above. Use PF 0.85 to 0.90
600 Volts is used for medium size motors 50HP to 500 HP, use PF 0.85 to 0.88

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