×
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

Switch / Harmonics
2

Switch / Harmonics

Switch / Harmonics

(OP)
Hello,

I have a spec that calls for a 600A, 5kV 3P load break switch (we usually use S&C alduti or miniputer).

The difference this time being the spec says the switch must be capable of making and interrupting its full rating including Harmonics...which are expected to be 30% current and 10% voltage...

I am contacting S&C to see if their switch is capable... however, I have not dealt with this before..what should be my concerns? 30% seems very high....is this typical?

Regards,
TULUM






RE: Switch / Harmonics

I really wouldn't worry too much.

Thirty percent current distorsion is not much at all. But 10 percent voltage is a bit high. I do not really see how that could make the job tougher for the breaker. A marginally higher crest voltage, perhaps. But definitely within normal voltage tolerances.

My guess is that a consultant put that in to make life more interesting...

Gunnar Englund
www.gke.org

RE: Switch / Harmonics

30% current distortion is not outside the realm of possibilities.  If you compute the effective rms value of the fundamental plus harmonics (square root of the sum of the squares), I think you'll find it isn't going to be much of problem for an air-break switch.  This should be confirmed with the vendor, of course.  As long as the effective current is within the rating of switch, I suspect it will be OK.  

Sounds like someone trying to cover every possible issue wrote your spec.    

RE: Switch / Harmonics

(OP)
Thanks again folks!  I am checking with S&C...

Anyone know of a good read on the subject?

Regards,
TULUM

RE: Switch / Harmonics

(OP)
This were it stands as of know (for interest sake)...

I checked in the IEEE 1247-1998 Standard for interrupter switches regarding the harmonic switching capability .  Under usual conditions the standard states "The harmonic content of the rated switching current shall be <10% and should cause no extraneous current zeros".  Being required to break larger harmonic currents above 1000V is classified as  'unusual duty' and is not covered under any specific standard that I know of...

Also, S&C has replied that "S&C has no recorded test data on  harmonic switching data, in Canada or the USA for either the Alduti-rupter or Minirupter" .   

Eventhough the harmonic currents are small and the switch is going to be underloaded I  am  suggesting that we  take exception to this requirement anyways... stating the above.

Regards,

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