×
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

transformer

transformer

transformer

(OP)
Hi forum members,

I need some expert advices on the following. I'm using a 380 V / 220 V transformer to supply some single phase loads. The site where I'm using this transformer is rated at 415 V 50 Hz. Ideally I should have got around 240 V output on the transformer at no load taking into consideration the turn ratio of the transformer. However, I'm measuring 250 V on the secondary side of the transformer at no load. Four transformers at different locations on the same site are behaving similarly.
Could the harmonics in the network cause these variations?

Grundig
 

RE: transformer

It's likely that your 415V nominal system is actually operating around 432V.

RE: transformer

Quote:

The site where I'm using this transformer is rated at 415 V
What is the measured voltage of the 415 V rated system?  Is this a solidly grounded system?  If so, why do you need a transformer to supply 220 V single phase loads?  Can't you just run a neutral and a phase to the load?

RE: transformer

(OP)
Thanks for the comments. The system operates on the IN network that is with the neutral isolated and single phase load are provided through step down transformers. The voltage measured is 410 V.

Guardiano

RE: transformer

The small transformer will be designed to provide rated voltage at nominal conditions which are likely to be rated output and 0.8 lagging power factor. If you reduce the load you will see the voltage rise, and at zero load it's not surprising that the voltage is high.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: transformer

I believed your primary neutral is floating. The secondary no-load voltage is always higher than expected. This is normal. Is your transformer connections is Y-Y.
The measured voltage 250V at no-load is due to the third harmonic component.

The line-neutral voltage will be reduced to 240V once you started to add load.

Alex

RE: transformer

If you measure 410V with transformer ratio you'll have about 237.5V and as ScottyUk says for let say range of 1000VA transformer have regulation of cca 5% so you got about 250V no load voltage

RE: transformer

Before I read rickei's post I assumed 5% regulation and calculated 249 Volts. Everything seems to be normal.

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

RE: transformer

What are the primay and secondary connections of this transformer?  Delta-Wye? Wye-Wye?

RE: transformer

I think the OP mentioned that it is a single phase 380/220 transformer.  So, there's no issue of broken neutral or delta-wye connection.

Guardiano, the values you measured looks normal (unloaded condition) as others have pointed out, and doesn't pose any danger to your equipments.

Is it at a telecomm switch?  Just being curious.  You mentioned IN network.

Regards
Rahul

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