Transformer X/R ratios
Transformer X/R ratios
(OP)
Hi
Does anyone know how to calculate or if there are tables that provide typical X/R ratios for power transformers in the IEC world?
Thanks.
Does anyone know how to calculate or if there are tables that provide typical X/R ratios for power transformers in the IEC world?
Thanks.






RE: Transformer X/R ratios
Or see Conrad St. Pierre's Short Circuit book.
David Castor
www.cvoes.com
RE: Transformer X/R ratios
You may find this extract from the AREVA T & D PRAG guide useful
RE: Transformer X/R ratios
Regards.
RE: Transformer X/R ratios
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(2B)+(2B)' ?
RE: Transformer X/R ratios
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(2B)+(2B)' ?
RE: Transformer X/R ratios
Pete-X/R will be almost same for 50 and 60 cycle area transformers.Utilities specify only X or rather impedance (in %) and not L,based on permissible regulation and SC currents. %X vary country to country ( eg generally UK has higher %X than US for same transformer rating range)R is not DC resistance,but load loss ( for large ratings AC resistance will be 20-30 % more)as % of rating.
For US market,as dpc said, red book gives X/R values .( Annexure 4A of IEEE 141-1993)But these values were taken from IEEE C 37.010 of 1979 -Application guide for HV circuit Breakers.C37.010 was revised in 1999. So fig 17 of C37.010 will be more appropriate.FOR IEC areas, typical %Z values are given in IEC/TR 60909-2ed2.0-2008 Short circuit current calculation - Data of equipment for short circuit current calculation.
For smaller units, the effect of load losses on x/R is more.But for larger unit loss value ( or efficiency) will not affect X/R much as X %is >>> R%
RE: Transformer X/R ratios
For X/R to remain constant irrespective of frequency changes would require R to increase roughly proportional with frequency (since X increases with frequency). I can understand there are some components of loss which increase with frequency^2 (like core losses, stray losses), but I would think for fault analysis we are talking about high current and the dominating resistance of interest would be associated with simple I^2*R losses which I think are constant with frequency. Am I wrong on that part?
Thanks.
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(2B)+(2B)' ?
RE: Transformer X/R ratios
Iam not sure whether Dc resistance or Ac resistance to be taken for calculation.I thought it must be AC. AC resistance will change with frequency.
R in today's transformers will vary from 1.5 %( 100 kVA) to 0.15 %( 500 MVA)
RE: Transformer X/R ratios
This has come up on Eng-Tips before re: ScottyUK & RalphChristie
Went under the name of AREVA PRAG (Network Protection & Automation Guide)
If you google AREVA T & D website (2011) this now comes up as AREVA T & D joins Alstom and Schneider .........I gather the GEC Althstom protective real guide was originally produced by the English Electric Co Ltd - The Protective Relay Guide. The relay division of English Electric, was at the St Leonard's Works, Stafford,UK was/is? the home of Areva T & D,now Altstom/Schneider Electric.
Also in the previous history GEC- UK > GEC- ALSTHOM > ALSTOM.
Try this site,let me know if you have any luck -I was able to download a free copy last year when it was AREVA T & D
Perhaps other members have a current link?
RE: Transformer X/R ratios
The following quotation is priceless: "Due to the popularity of this publication, the hard-copy version of the NPAG is no longer available."
Only the bloody French could cease population of such a popular book because it was too popular.
I have a downloaded copy of the PRAG and a copy on CD. I'll upload it to a filehost - I think that should be ok legal-wise as it was public domain when published and is un-altered.
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If we learn from our mistakes I'm getting a great education!
RE: Transformer X/R ratios
Long live GEC!
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If we learn from our mistakes I'm getting a great education!
RE: Transformer X/R ratios
The range of the X/R ratio per recent IEEE transformer Committee documents indicated the following:
a) Small power transformers: 15 <X/R< 40
b) Medium power transformers 35 <X/R< 70
c) Large power transformers: 40 <X/R<125
This is fairly close to the IEC parameter shown in the attachment.
RE: Transformer X/R ratios