×
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

Excessive Neutral Current

Excessive Neutral Current

Excessive Neutral Current

(OP)
All,

Is there a standard or reference out there describing neutral current or voltage/current imbalance limits (three phase 4.16kV wye overhead, United States)? I'm working on a study and am finding imbalance as much as 30% which I know is high, but I'd like to be able to point to a standard.

Thank you

RE: Excessive Neutral Current

Annex C in the above recommends a voltage unbalance of no more than 3%. The accompanying graph shows a motor derating factor of about 0.9 at the 3% mark.

RE: Excessive Neutral Current

There is no standard for current imbalance. Neutral overcurrent relaying on a feeder cannot be very sensitive with a high imbalance, and you have to account for the possibility of a single phase branch fuse blowing as well. Losses and voltage drop on the distribution system increase considerably with imbalance. Correcting imbalance to some degree can usually be justified by loss reduction and/or voltage drop reduction.

We have used a criteria of 15% maximum current imbalance in studies. We have recommended shifting loads to achieve 10% if the imbalance is more than 15%. This is based on the practicality of shifting loads, however, not on an industry standard.

One problem with studies is that records of what phase transformers are connected to are often not accurate.

RE: Excessive Neutral Current

With present day electronic loads at distribution level, neutral may carry substantial third harmonics currents, sometimes exceeding phase current.So in K -Transformers neutral leads are made with same or more area of cross section as line leads.

RE: Excessive Neutral Current

To qualify for BPA's distribution efficiency funding, BPA requires no more than 15% imbalance and no more than 40A of neutral current. http://www.bpa.gov/energy/n/industrial/Distributio...

Although we are attempting to achieve this goal, there are some feeders where phases have variations in daily or seasonal loading (i.e. phase A is always high in the summer/day but phase C is high during the winter/night). We also have a number that are reasonably balanced on normal load days, but are dramatically more unbalanced during extreme temperature.

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