1*400 mm^2 copper conductor. You have to check your conditions if it is underground [earth thermal resistance, distances between cables or ducts, depth and other].It will be better if you will consult a specialist.
An overhead transmission line it will be preferable [it is cheaper!].
Given how critical is this connection, if this is a power plant a transmission line may not be a good idea due to critical outage consequences (cables are strongly recommended in this case especially if crossing roads).
If you are in AIS, you can use an OHTL, will be about 8-10 times cheaper than a cable.
If you decided to go by Cable,
Size should be 2 nos. of 400 sq.mm copper conductor (considering cable derating also) and based on 130 MW (710 Amps), length 500 M.
