×
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

Fault Contribution from Radially Fed Distribution Transformers

Fault Contribution from Radially Fed Distribution Transformers

Fault Contribution from Radially Fed Distribution Transformers

(OP)
I'm having some trouble understanding why a radially fed transformer can be a source of fault current during an upstream fault.

SYSTEM:
[TRANSMISSION SYSTEM 25kV BUS]---[25kV BKR]-----------------------[FAULT]--------------------------------[TRANSFORMER]

I've heard that, for certain faults, the downstream radially fed transformer can act as a source (even without generation) and contribute to the fault.
However, I am having some trouble understanding this. I believe that it also depends on the configuration of the transformer and the type of fault. So, for upstream ground faults, any downstream transformers that are delta primary would not contribute to the fault.

Could anyone either shed some light on this, or link to a paper that explains this fault contribution from a downstream radially fed transformer?

I should note that there are no sources other than the transmission system in this scenario.

Thank you!

RE: Fault Contribution from Radially Fed Distribution Transformers

Downstream transformers can provide fault current in two ways:
1/ If there are any motors connected as loads, these will contribute to the fault (capacitance could as well, but it's generally not as much of a concern). On a distribution system, this would be the most common way.
2/ If the transformer is connected as grounded Y on the HV side and has a delta connection as either the secondary or tertiary, this will be a return path during ground faults, making the transformer a zero sequence source. This is not so common on a distribution system since it would be an unusual transformer connection.

RE: Fault Contribution from Radially Fed Distribution Transformers

The issue arises with one or two single phase to ground faults.
The feed back from a wye delta transformer is of most concern if the primary wye point is connected to the system neutral. In most cases grounding the primary wye point will effectively be a connection to the system neutral.
If the primary wye point is floating in relation to the system ground the feed back effect is very much less.
A transformer with a three legged core will develop a "Phanton delta". The comments as to the wye point connection to the system neutral still apply.
In the worst case the back feed current will be limited by three times the transformer impedance, (plus asymetrical effects).

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

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