×
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

Voltage Levels

Voltage Levels

Voltage Levels

(OP)
We have a project were the engineer has requested to modify our 21kV transformer taps in order to achieve a secondary voltage level of 510V. I know motors have rating of +/-10% so it should be Ok. However I would like to understand other impacts

RE: Voltage Levels

That's pretty high for a 480 V nominal system.  Remember the plus 10% for a NEMA motor starts at 460, not 480. So you'd be at +9% at the bus (voltage the motor will be lower, of course).  Probably still OK, but what if the primary voltage goes up a percent or two?  

Basically, everything will be seeing a high voltage, including all of the 120 V, 208 V, and 277 V loads, unless the taps of all of these transformers are adjusted.  

Motors and transformers are probably the main concern, since they operated pretty close to magnetic saturation due to economics.  

Motor operating parameters such as efficiency and power factor are based at operating at nominal voltage, so these will definitely change if you operate them at +9%.   

RE: Voltage Levels

(OP)
Tnkas DPC, when you state 9% at the bus? What do you mean. Is it a deviation at the output of the transformer of 9% and then 1% voltage drop at the motor feeder?

RE: Voltage Levels

Oops - calculator operator error.  510 V would be 111% of 460 V.  Sorry about that.  The voltage at the motor will be lower, but that would be too high a bus voltage for me.

 

 

RE: Voltage Levels

How about equipment smoking hot? Is this a new installation project or really a modification?
Transformer get hot when operated at higher than rated voltages. I can still remember the smell of frying winding insulation in that case.

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