×
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 neutral Grounding
2

Transformer neutral Grounding

Transformer neutral Grounding

(OP)
Under what conditions the promary and secondary neutrals of a Y Y power transformer can be connectec to a common ground bus that is bonded to main ground grid. I have recently come across this situation at a very old industrial SITE. Any comments, reference & suggestions aare most appreciated.

Morrison Dean

RE: Transformer neutral Grounding

2
You may be hard pressed to get a pat answer.  It would almost always be case dependent, and be effected by impedance paths during fault, transient and unbalanced conditions, and reactances of bus/cable component dimensions and spacing, aside from various conductor sizes.  A concern could be the case of a significantly higher impedance path from the common bus to the ground grid than the individual impedances from transformer neutral connections to the common bus.  A worst-case condition may cause elevation of the lower-voltage neutral to raise significantly above ground potential {with consequent insulation damage} caused by a primary-side/higher-voltage-system ground fault.  [Distribution voltage assumed.]  

IEEE C57.105 “The YG-YG should not be used except on 4-wire effectively grounded primaries as it merely carries the system ground through the transformation…”  “If the connection is such as to permit this condition on the primary side, the transformer will supply part of the unbalanced phase-to-neutral loads and line-to-ground fault currents.”

IEEE C62.92.4 “If a primary-to-secondary fault developed within the transformer and the neutrals were not connected, the resistance of the return current path could be so high that not enough fault current would flow to enable the primary protective device to clear the fault. High voltage would then be impressed on the secondary for an extended period of time, posing a risk to humans, animals, and equipment.”

A hung jury, of sorts?  Review the entire text of standards in making your determination.
  

RE: Transformer neutral Grounding

Suggestion: Ygrd-Ygrd is often used in power distribution network transformers, where there is relatively balanced load and minimal zero sequence component passing through the transformer. Any other winding connections for this type of transformer are considered less advantageous.

RE: Transformer neutral Grounding

jlazucena
I would like to add balanced voltages in the primary of the transformer to jbartos post, only as a clarification because "minimal zero sequence component passing through the transformer" implies balanced voltages

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