Contact US

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!

*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

VFD application to standard duty motor

VFD application to standard duty motor

VFD application to standard duty motor

Customer has 3 each 75 hp Reliance standard duty motors, 4 pole, 460 vac, tefc that run from ROM stacks of coal for train loading.

They need to start blending these stacks and want to slow down the feed on the belts based upon sulphur content etc.

The worst scenario the engineers can see is slowing to 10 hz which at this speed will require only 5 hp and only for a maximum of 2 hours while the train is loading.

Question: Besides the obvious concern about a non-inverter duty winding system, will cooling be a factor for this type of time duration at this minimul load since air over will be reduced to 1/6 of original volume?

RE: VFD application to standard duty motor

Yes.  Add blowers to those motors that run independently of the motor power whenever the VFD is in the "Run" mode. That way you will not need to worry about any operating speed.

Curious, how did they come up with 5HP at 10Hz on a constant torque application like a loaded conveyor belt that required 75HP at 60Hz? Are they simultaneously reducing the amout of coal fed onto the belt as the speed is reduced? And even if so, what about the material that was already on the belt when the decision was made to slow it down? That should theoretically require the same torque as it previously did until the heavier section passes the load-out. Something doesn't sound right in those numbers.

HP = Tq * Sp/5250  So at 75HP and 1750RPM, Tq was 225ft.lbs.
To get the same Tq at 292rpm, the HP would be 12.5, assuming the same load.

Not that it will make any difference in your application, the motors and drives will still work fine as long as you cool them properly. Just curious.

Subvert the dominant paradigm... Think first, then act!

RE: VFD application to standard duty motor

jraef is probably right as usual, but to me it's not a straightforward answer.  Yes cooling flow will be reduced 1/6. Perhaps heating (approx no-load heating) will be aprox 1/2 of full-load heating.

TEFC conducts heat to the fins where it is removed to the air. Even with no air flow it seems conceivable that natural convection heat removal from fins might get you 50% of the heat removal that you get with full air blowing (assuming similar stator temperature). And you do still have 1/6 air blowing. And you will only run that for 2 hrs. I'm sure Reliance could do a study on that without too much trouble.

RE: VFD application to standard duty motor

Hi good day

My experience tells me that you would have trouble
operating TEFC motors at 10hz  on a constant torque application without overheating same.External cooling blowers might be necessary.



RE: VFD application to standard duty motor

In constant torque application the power is reduced with speed (+ add excitation and losses).
Check control range in motor data sheet. If it is lower than the required 1:6 the motor will heat up (assuming the cooling fan is motor shaft driven). You will need external cooling.
Note that airflow is reduced proportonally to the square of the rotatinal speed.

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! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close