×
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

VFD FEDDING A POWR TRANFORMER

VFD FEDDING A POWR TRANFORMER

VFD FEDDING A POWR TRANFORMER

(OP)
Dear All ,

We are developping a motor control test center project, and some of our collegues are suggesting to use a VFD to fed a power transformer in order to change the transformer´s voltage output  with out change the frecuency, this is intendded for no load test.

Any one with similar experience ? pros and conts??

Thanks for the Inputs

Petronila

RE: VFD FEDDING A POWR TRANFORMER

Hello Petronila,

Did this about nine months ago. But used the output of the transformer to start a synchronous 11 kV 6 MW motor. The inverter was a 500 V 840 A rated inverter.

That application was OK. But, if you want to have a clean sine output from your secondary, you probably need to filter the VFD output heavily.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: VFD FEDDING A POWR TRANFORMER

Skogsgurra
Apparently you didn't have any problems burning through the transformer winding insulation like you can do with cheap motors.  Did you specify special insulation?  The distance between the inverter and the transformer was probably very close.

RE: VFD FEDDING A POWR TRANFORMER

Yes, quite close. I would say 15 metres/50 feet.

The transformer was an existing one and it was oil isolated. So no problems with corona. And no special insulation.

Also, it is only used during start up of the refiner motors and that takes less than two minutes. The refiners then run for typically a week or two. So even if we got some ozone production, it wouldn't accumulate.

I think that PWM and insulation can be a problem with smaller transformers. But larger ones, like those found in a typical motor repair shop, are not exactly "rush wound" and there is plenty of distance between windings and iron, too.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: VFD FEDDING A POWR TRANFORMER

Seems like a serious overkill to just change voltage alone. You could do that with a phase angle SCR controller; it's done all the time like that. The only reason to use a VFD is if you want to change the frequency.

RE: VFD FEDDING A POWR TRANFORMER

(OP)
Yes jraef ,
If you see the project like you are going to buy the VFD For only voltage variation you are right,is an overkill , but this VFD are intended  to powered the low voltage motors up to 660 Volts.The idea is to have the initial    VFD`s investment in order to fed one dry type tap transformer and have variable  secundary voltage avoiding the use of CTV Transformer.

Attach you will find the design.

Thanks and regards

Petronila  

RE: VFD FEDDING A POWR TRANFORMER

I've done this in the past on a couple of jobs and I definately recommend a filter to protect the motor. I think I remember something like the capacitance of the circuit goes up by the square of the transformer ratio so the voltage spikes on the motor will be high if you do nothing. A sinewave filter on the drive O/P is one option and I used the transformer and capacitors on the HV side very succesfully.
The transformer manufacturer should be informed of the PWM characteristics of the drive output.
I had a problem on one site where the step-up transformer was heating up excessively and this was solved by reducing the motor flux parameter in the drive. The application was a 6kV fan and dry type cast resin transformer so the windings were aluminium strip/sheet.

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