×
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

SF6 Breaker Voltage Transient Failures
2

SF6 Breaker Voltage Transient Failures

SF6 Breaker Voltage Transient Failures

(OP)
We recently turned back on an indoor 27.6 kv. SF6 breaker feeding a transformer with no connected secondary load.At the instant this breaker closed(connected on the same 27.6 kv.bus) an indoor nearby 27.6 kv. loaded dry type transformer flashed over ( high voltage winding terminal to ground).

Doing some research, it would appear this is a common problem with using SF6 breakers and dry high voltage transformers.One group is recommending installing snubbers ,claiming they will attenuate this high frequency voltage transient better then the installed lightning arrestors.

The transformer now needs to be repaired.We do not want to repeat the same type of electrical failure again.Do we need to install snubbers everytime when there are SF6 breakers and high voltage dry type transformers?

RE: SF6 Breaker Voltage Transient Failures

Snubbers will do a better job of attenuating ferroresonant conditions than relying on lightning arrestors. The margin between the normal system voltage and the LA's operating point is too great and its possible that some overvoltage condition that lands within this margin can damage the transformer and still not be caught by the arrestor.

As to whether you'll have to install them every time: That depends on your ability to do an analysis of each system to evaluate the probability of such a condition occurring. If you feel that this is within your capability, then you might be able to rule out some snubber installations.

RE: SF6 Breaker Voltage Transient Failures

Problem faced by ghostbuster7 is known to industry from 70's and suitable solutions are offered by breaker manufacturers/system planners. Problem is more with vaccum breakers.A snubber ( Capacitor and resistor in series to line and earth) is the usual solution. You can get more details from IEEE draft standard,
PC57.145/D5.2 ,Jan 2009, " Guide to describe the occurrrence and mitigation of switching transients induced by transformer,breaker and system interaction" and also breaker amnufacturers like ABB,S&C Electric.

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