×
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

Heating of motor by using frequency converter

Heating of motor by using frequency converter

Heating of motor by using frequency converter

(OP)
For checking of operation of frequency converter (4kW 3 phases 400V)we use 0.75kW motor. Unfurtonately motor heats more than it could be.
The frequency converter on my opinion was programmed correct. The rated current of the motor is 2.3A, but measurings shows that it is 3.2A.
Is this converter's programm's mistake or something is doing wrong?
Or this is motor fault?

RE: Heating of motor by using frequency converter

Have you looked for an overload?  The drive you have is greatly oversized for a .75kw motor and will give the motor all the power it can handle plus some more.  You may wish to double check the current limit you have programmed.

RE: Heating of motor by using frequency converter

What kind of amp meter are you using to measure amperage?  The output of the VFD is not a standard syn wave and can not be measured with the common digital meters.  Use either an old style iron movement meter or a true RMS meter.

What does the VFD say the output current is?

RE: Heating of motor by using frequency converter

Check the motor specs, most motors cannot tolerate low Freqencies unless they are designed for it. Typically if the application calls for less than 20Hz I would use a speciallised motor for VFD application.

RE: Heating of motor by using frequency converter

I agree with acadien, the cooling fan on the motor is sized for the designed speed. If you run the motor at a much slower speed it will require an external cooling blower.

RE: Heating of motor by using frequency converter

Suggestion: The frequency converter in lightly loaded condition may be noticeably less accurate than for the rated conditions.

RE: Heating of motor by using frequency converter

What type of load: Constant Torque or Variable Torque ?
What is the operating speed range:  ?Hz to ?hz
Are you getting hi current at all speeds ?
Is the VFD a regular V/Hz drive ?
What is the carrier frequency ?
What is the output voltage ?(use a true RMS meter)
Is this a new application or retrofit ?

RE: Heating of motor by using frequency converter

Motor efficiency is essentially hit by frequency converter / inverter / PWM amplifier operation that causes additonal loss / heating.

Of additional PWM losses mechanisms - copper ohmic, iron eddy current and hysteresis loss - eddy current PWM induced loss is likely dominating for conventional iron machine (this is not the case of pancake ironless brushless motor).
 
More info is supposed to be found at
http://www.drbrushless.com/articles/ironloss/
 
-Alex V.

RE: Heating of motor by using frequency converter

Hello wiks

The most common cause of a problem like this is because the motor is being driven overspeed with a load that increases with speed. (Fans pumps etc) The second most common cause is because the output voltage setting of the drive does not match the motor, and the third most common reason is the measurement of the current. It must be measured on the output of the drive (not the input) using an instrument that is not affected by harmonics. i.e. it must be a true RMS measuring device.

Best regards

Mark Empson
http://www.lmphotonics.com

RE: Heating of motor by using frequency converter

Suggestion: The motor may draw more current if the motor input experiences a higher harmonic content than the one it was used for setting the motor nameplate rated current.

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