×
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

Minimum RPM for TEFC motor

Minimum RPM for TEFC motor

Minimum RPM for TEFC motor

(OP)
We are using a VFD to control a 3/4 HP, TEFC, 1800 RPM, 1.15 SF motor with rolled steel frame. The Application is constant torque (positive displacement pump). The actual HP (at full speed) is only about 1/4 HP. Is there any way to estimate the minimum RPM for the motor without overheating. We want to operate at 12Hz. If we test this using trial and error, what should the max. frame temperature be? Are there other issues besides temperature that we should be concerned about?

RE: Minimum RPM for TEFC motor

If the rolled steel frame is in direct contact with the stator core, the top dead center temperature measurement (out of air flow) should be approx 10C less than average coil temp. However the hot spot of TEFC motors is usually the end turns - add another 10C for hot spot. A round about way of saying add 20C.

I would think you should have no temperature problem at 12HZ and 33% load.

Caution: if the motor has overbolts, sometimes they complete a circuit and overheat. If so, Change to non-magnetic SS bolts.

RE: Minimum RPM for TEFC motor

Another idea.  Check with the manufacturer to ensure that you are operating in the listed speed range of the motor.  For example, 10:1, 100:1, 1000:1.  

Manufacturer lists speed range at which motor may operate at full torque without overheating and committing thermal suicide.

1800RPM/360RPM = 5:1 speed range.  Should be okay if motor is rated for inverter duty.

I esitmated you are operating at 360RPM with the assumption the motor is rated is for 60Hz operation, and your listed 1800 RPM specification.  

RE: Minimum RPM for TEFC motor

Your question can be most adequately answered by the motor mfr.  In general, TEFC is not the best choice for running slow, since proper cooing depends on the fan speed.  I would anticipate a need for supplemental cooling at lower than 40hz (assuming the mtr is vector duty).  You could help yourself by changing to a TENV (vector duty).

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