×
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

Seconday Current during Power Transformer Energization
2

Seconday Current during Power Transformer Energization

Seconday Current during Power Transformer Energization

(OP)
Hi,
We recently energized a 166MVA power transformer (230kV / 34.5kV --Grounded Wye / Grounded Wye thru resistance). We recorded currents on the primary and secondary side. The primary currents were as spected (~2000Amps) but I was surprised to see current on the secondary side, these currents aren't big in magnitude ~2-3Amps. Do these currents come from the capacitance of the secondary bus? The seconday CB was open so there was only about 15mts of insulated cable.

Cheers.

RE: Seconday Current during Power Transformer Energization

There is a fair amount of capacitance within the transformer itself.

RE: Seconday Current during Power Transformer Energization

If by "primary currents" you mean currents on the 230 kV side, I'd be shocked if you saw 2000 Amps. For a 166 MVA transformer, rated current on the 230 kV side is 416 Amps.

With the exception of exciting current (which is very small, usually less than 3% of rated current), you shouldn't see any current on the primary if there's no current on the secondary.

Excluding exciting current, the following equation should hold true:

Vprimary*Ipimary = Vsecondary*Isecondary

RE: Seconday Current during Power Transformer Energization

Doesn't transformer inrush range from 5-20X the full load currents? 2000/416=4.8 so seeing 2000A for a moment on the primary side wouldn't be that far off

RE: Seconday Current during Power Transformer Energization

Yeah. You're right. But, inrush is going to have a really strange shape when compared to fundamental current. I'm not sure why I assumed he was referring to fundamental current, but that was my mistake.

RE: Seconday Current during Power Transformer Energization

The charging current for 15 m of cable would be about 0.07 A. Charging current for the transformer capacitance would not appear in the secondary leads.

RE: Seconday Current during Power Transformer Energization

Do you have a one-line you can post ?

Is this a constant 2-3 amps in question ? Or was it just momentary as per inrush current (12 cycles duration there about) ?

RE: Seconday Current during Power Transformer Energization

Some noise.

RE: Seconday Current during Power Transformer Energization

In my opinion this is inrush current in the primery side of transformer. This is 2-nd or 5-th harmonic, but it's important to know how many periods is this 2000Amps?

RE: Seconday Current during Power Transformer Energization

Hard to comment without knowing the test/measurment set up...

The 2000A primary sounds right for short time inrush. If you have oscillography, the waveform is interesting to look at.

2 - 3 amps secondary sounds off to me... Check to make sure the primary and secondary measurment leads you are using aren't close together or coiled around one another... possible its just induction you are reading. Was the measurment taking in a live switchyard?

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