400 hertz derating

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Navy-Sparky

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Does anybody know of a specification that clearly states the derating factors for wiring and overcurrent calculations to take into account the reactance within a 400 hertz power system? Presently I am using derating factors out of an old Mil-Spec based on number of aircraft loads. Wiring configuration consists of three sets of parallel conductors around an oversized neutral. Do the wires require derating based on reduced reactance? Usually an aircraft power converter must meet 300% overcurrent for 6 second and my contractors typically derate breaker by only 50%, is this the correct factor considering most manufacturers only provide a 200% overcurrent for 10 second?
Any feedback would be welcome.
Thank you,
Navy-Sparky
 
Navy-Sparky said:
Does anybody know of a specification that clearly states the derating factors for wiring and overcurrent calculations to take into account the reactance within a 400 hertz power system? Presently I am using derating factors out of an old Mil-Spec based on number of aircraft loads. Wiring configuration consists of three sets of parallel conductors around an oversized neutral. Do the wires require derating based on reduced reactance? Usually an aircraft power converter must meet 300% overcurrent for 6 second and my contractors typically derate breaker by only 50%, is this the correct factor considering most manufacturers only provide a 200% overcurrent for 10 second?
Any feedback would be welcome.
Thank you,
Navy-Sparky
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Check at the bottom of this article http://www.anixter.com/./AXECOM/AXEDocLib.nsf/(UnID)/7B02465D0630940680256F250068807D/$file/WCTHContentsElectricalCharactersitics.pdf
 
I assume that you are talking about circuit breakers. The derating data that I have for older Westinghouse breakers varies from 10% to 50% depending upon the frame size and the ampacity range within the frame size.
I have table with specific values for them. In general the lowest ampacity within a given frame size is generally derated about 10% to 20% for the highest ampacity for the smaller frame breakers to 50% for the larger frame breakers.
These are general observations on what one can expect to see. If the manufacturer doesn't have published deratings then there is no magic formula that could be applied.
Check this document out, it's the one I am referring to.


http://www.eatonelectrical.com/unsecure/cms1/MR08703002E.PDF
 
Thank you all for the information on 400 hertz derating

Thank you all for the information on 400 hertz derating

I have been able to glean from the information provided that the derating of the circuit breaker is manufacturer specific and depends on installation method which could result in 20-33% derating. My contractors seem to be derating the circuit breaker based on the required short circuit typical to most power converters.
The wiring derating is based more on construction of cabling or wiring configuration and deals mostly with voltage drop as a function of reactance on length of run.Typical derating is 15-20% but is best served by field calculations based on wire aspects typically provide by most manufacturers or in code book. MIL-HDBK-299 provides some information on different cable construction and characteristic, but is primarily discussing delta power for ship board systems versus wye based shore installations.
I have been using UFGS 262543 and UFC 355501 for most of my information. My typically system configuration is less then 250 feet of service feeder and an aircraft service cable of 60 to 150 feet from a Line Drop Compensator with 15% regulation via taps.Presently we supply 100 amps, but rescently 200 amps of service is becoming a requirement, hence my reason for inquiry.
I think I have enough information to better comprehend my system, but feel free to provide any other information you might have.
Thank you all very much for your professional input on this subject.
Navy-Sparky (Karl)
 
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