conductor size

More info needed. How long is your cable? Two hundred meters? Two hundred thousand meters? There will be I²R losses in your cable. R, in turn, depends on the cable length, conductor material resistivity and conductor cross-sectional area.

There may be non-trivial losses to the cable's surroundings (damp, conductive earth, metal structures, etc.), say, if the cable is expected to span distances of hundreds or kilometers or more. Your cable size will depend in part on how many losses you can tolerate. Your cable will have a voltage drop (think of the cable as an extended resistor). At 132 kV this is unlikely to be a problem, but can be a real consideration in some situations.

My answer to your question assumes that you are asking from the perspective of an engineer who might be called upon to consider such factors in the design of, say, a cross-country power transmission line. But your motivation for asking may be quite different. It may be helpful if you said something about your motivation for asking and the level of detail you'd like to see in our answer. Are you looking for a simple "ball-park" figure, perhaps, or something a bit more rigorous? Things are seldom as cut-and-dried as they appear - even when it comes to what is essentially a length of "wire." Welcome to the Real World, Neo.

thanks for responding so soon

i am asking abt a power plant which has the capacity of 25 mw power generation.the transmission is then going through a 132 kv substation..the ampere maybe 300 A

now to connect from 132 kv substation to grid lines ACSR bare conductor is going to be used

lets assume the distance is 200 meters..now my question is what should be the cable size..how can i determine this?

If you have a conductor that conducts at 100 S/cm how much current could you move through it at high voltage and how much at low voltage