Bare Copper Conductor Sizing

Have you tried Google?

TonyS, I am sure the OP is waiting for CR4's resident Google Engineer Mr Lynlynch to perform the google search. Using Google is one of lyns strongest (only) ability.

Let's hope that no one can ever touch this "bare copper conductor"!

Since you didn't bother to tell us where you are, try either NEC or BS, or maybe even ASTM or NEMA.

If you don't know what any of these are, never mind.

While not sure... I think he was asking about the conductors feeding the transformer with primary voltage and taking the secondary source away to the distribution. But... it is a crap shoot either way.

Though I did enjoy your response.

Thank you Redfred for taking (Your) Time to explain some very relevant points in a polite and humorous manner. GA done well.

DEAR GUEST!!!

Be specific with your quiries or question. Bare copper conductor? Are you referring to the earthing system or simply the feeder cables sizes via primary incoming overhead transmission lines to handle the full demand load of 40MVA, 132/11KV.. refers to primary or secondary sides?.SF6 normally used in HT/MV step-down substation . To calculate the feeder sizes distance between the transfo to the supplied load and the capacity of connected loads will be considered in order to maintain the line voltage regulation not to exceed 5% at the farthest point of the circuit. The basic formula is P=sq.rt of 3 x V x I x PF of the system. Theoretically this formula is only the basis of determining the full load current of the machines x 1.25 (NEC) will be your cable size then refer to cable manufacture's data. But once your machine or transformer is on-load at certain distance from supplied load/s then it is expected that there is the amount of voltage drop/s along the lines both primary and secondary sides. That is why the cable sizing does not satisfy the formula as mentioned above it must be a point-to-point basis calculation in order to arrive into right-safe cable sizes as per cable manufacturer's standard cable current carrying capacity data. One more important is dont miss to calculate the short circuit fault currents and provide protective device so that your 40MVA transfo is safe.

BS 7671

courtesy:-pwslack

Dear Dear! Please give some respect to the knowledge and skill of we EEs. In engineering "responsible" behavior is to base things on "exact" or "approximately" exact data and not forget related dangers or eventualities. So if the question is not clear, how can a clear answer be provided and that too in less than 100 words. The best answer, in one word would be NO! Who said, "Learn to say no. If you say yes then keep it".

I recommend contacting a design engineering firm to answer your question, instead of an online forum. Information posted here may not be vigorously researched. But as a start, look here:

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet46

Assuming a three phase transformer, max MVA of 40 (?), standard HV taps (?) [check transformer nameplate]:

Base HV current rating is 40 MVA / (132 kV X 0.95) / sqrt(3) = 184 amps

Base LV current rating is 40 MVA / 11 kV / sqrt(3) = 2100 amps

May need to uprate based on ambient temp, windage, and short circuit requirements.