×
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

Auto-transformer - Earth Leakage Problem

Auto-transformer - Earth Leakage Problem

Auto-transformer - Earth Leakage Problem

(OP)
We have a piece of equipment which was designed to be supplied by 1000VAC, the customer informed us late on that the supply would be 1100VAC.

As a solution an auto-transformer was used to drop the supply to the designed level.

Now when the power is applied the main breaker trips due to the transformer centre tap being connected to the earth instead of neutral.

There is no available neutral to the equipment which is remote and we cannot install a new earth.

What would be the result of disconnecting the earth and leaving the unbalanced load floating?

Is there another solutuion apart from replacing with larger, heavier, expensive alternatives to the auto-transformer?

RE: Auto-transformer - Earth Leakage Problem

Use an open delta auto transformer. There is no neutral, no ground connection and no phase shift.
Step 1: What is the current draw?
Step 2: Choose two transformers with a)
A rating of 1000:100 Volts.
A current rating on the 100 Volt winding that equals or exceeds the current draw of the load.
Rated for buck boost service.
Connect the two transformers in open delta auto transformer configuration.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Auto-transformer - Earth Leakage Problem


In applying an autotransformer, it's important that both windings be insulated for full line voltage; i.e., in this case, the 100-volt winding also needs to be intended for 1100-volt operation.  
  
 

RE: Auto-transformer - Earth Leakage Problem

What busbar said. A conventional transformer rated for buck-boost service will meet this criteria and may be connected as an autotransformer.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Auto-transformer - Earth Leakage Problem

(OP)
Thanks for replies, we're tallking with the manufacturer about wiring as Delta now.

Just as a footnote though, we're dropping 100V, from 1100 to 1000, not dropping to 100V.

Its only a small amount, but apparently a big difference in that at 1000V it can be catagorised as a low voltage machine.

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