what the size of power cable 3 core for motor 18.5 Kw with star dalta starter?

Answer 1

Full load current is 32 amps,phase current is 18.4 amps Hence 3 core 15 sq.mm power cable is req.or 3 core 6 sq.mm 2 nos of cables req. to connect motor to starter.

Answer 2

It is entirely dependent on the voltage supplied to the motor.

At 230 V (wye connection to motor), rated current is 80 A.
At 460 V (wye), rated current is 40 A.
At 600 V (wye), rated current is 31 A.

Different cable sizes required for each rating (for minimum cross-section) ... however, cable sized for 80 A will certainly do the job for the higher voltage ratings, assuming it is insulated for the appropriate voltage.