×
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

How clos is inrush point to the curve

How clos is inrush point to the curve

How clos is inrush point to the curve

(OP)
Attached is a result of coordination study of a fault fiter fuse( S&C ) and low voltage ckb. What margine need to exist between the inrush point and the fuse curve to safely order the fuses?

RE: How clos is inrush point to the curve

Hum, that's a good question

I assume that the point is draw at 12x nominal current of the transformer.  This is a conservative assumption, since every transformer is different and the utility impedance will limit the inrush current.

So if the curve doesn't touch the point, this is probably good.  I saw a transformer with an instantaneous at 8x is nominal current, but it work fine, so why fix it.

The 12x point is to be sure, when the coordination is tight, I assume that it is less than that.

RE: How clos is inrush point to the curve

(OP)
Well, Tx is 3000/4000KVA- 27.6KV/.6KV 10.8 % impedance, calculation shows 8X inrush point, so as manufacurer recomendation.
How would I be certain to tell the customer to change his existing fuse to fault fiter, spend alot of money and then , it trips for inrush.....
even if we measure the inrush..it might vary right?

RE: How clos is inrush point to the curve

I cannot read your time scale. 12X is generally plotted at 0.1s for hot-load inrush. Is your 8X at 0.1s?  If you expect to pick up motor loads or lose diversity following an extensive outage, consider adding cold-load inrush points at 6X for 1s, 3X for 10s, and 2X for 100s. Join all points with straight line segments to produce an inrush plot on your plot.

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