×
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

EAF transients

EAF transients

EAF transients

(OP)
Client has been having irregular 11kV VT failures on an submerged arc furnace installation. System details as follows:
- 2 x VTs per furnace 11/28/75kV connected phase to phase upstream of the furnace breaker.
- Supply transformer 88/11kV 75MVA.
- 4,8 MVAr plain capacitor bank switched with the furnace.
- 30 MVA Furnace fed via 3 single phase furnace transformers.
- Furnace breaker - air blast.
- Failure is external flashover on VT connection leads.
- There is a second furnace connected to the same supply transformer.
- surge arresters on one furnace only (the one with the failures, however connected downstream of the furnace breaker).
- No VT failures on the other furnace.

I am pretty sure that the failures are simply due to external flashover due to badly installed VTs. However, what interests me is a transient that was recorded.

High speed voltage transient measurements were connected to the open delta output of the VTs (i.e. upstream of the furnace breaker). During furnace overcurrent trips (not at light load) on the first day two events were recorded which showed medium frequency voltage oscillations (approx. 17kHz) exponentially damped (dying in approx. 0,4ms), magnitude about 2p.u. Funny thing is that these appeared on all three traces (measuring phase to phase) simultaneously.

The traces were not seen again during the two week measurement period. I do not know of any system changes during the period - strange ??

I assume that this is restrike with some kind of coupling through the two capacitor banks. Is there anyone who can explain this in more detail or comment.

RE: EAF transients

Could it perhaps be a resonance condition at 17Khz being excited by the arc from the airblast breaker?  (I don't think restrike is commom with air-breakers, vacuum mainly)

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