Switch / Harmonics 2

[tulum]

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

 

[Skogsgurra]

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

http://www.gke.org

 

[dpc]

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.

 

[tulum]

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

Anyone know of a good read on the subject?

Regards,
TULUM

 

[tulum]

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,