×
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 protection Curve

Transformer protection Curve

Transformer protection Curve

(OP)
I am in the middle of a discussion with an equipment supplier who is saying my fusing for transformer protection is undersized per his tables. I have modeled the curve in ETAP using the FLA of the transformer and plotting it against the magnetizing inrush and the damage curve.

Is the 1.4 FLA suggested by the manufacturer just a very high safety margin?

RE: Transformer protection Curve

The upstream fuse is basically to offer transformer primary side main protection and the back up for the secondary side faults. Assuming that there is a protective device existing in the secondary side.

From the TCC curve you posted transformer it is clear that the transformer is protected for the through fault current. Hence the fuse rating appears to be fine.

Please remember that the veiws may vary from person to person, as there is no hard and fast rule on this.

RE: Transformer protection Curve

I'm a little confused by where the FLA of ~3000A was plotted. Your x axis is current x10, but it appeared to be plotted in the 300A range. Same comment applies to the inrush dot @ 12x for 6 cycles.
Is the primary voltage 8.3kV, or is that just the rating of the fuse?

Something seems a little off here.

RE: Transformer protection Curve

@distributionPlanner,
The plot is on the 4.16kV level. FLA at primary is 346.97 A. Equivalent X 12 = 4163.64 A.
@NJWVUGrad,
IDK how it is with other engineers but I prefer sizing fuses to cover for short-circuit and allow the secondary breaker protection relay to cover for the transformer overload and short-time duration loading.

Your fusing ratio is around 2.59, which seems okay (=>300%). From your fuse TCC, at 12 X FLA = 4163 A, your 400A fuse will clear at around 0.15 seconds, just a bit higher than the criterion of 0.1 seconds (6 cycles) of inrush. At 25 X FLA = 8674 A, your fuse will clear in around 0.023 seconds, higher than the 0.01 seconds (3/5 cycle).

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