What is Cable Size for Induction Motor 30 kW Delta Star?

It depends. 64A x 1.25 = 80A.

For 30°C (86°F) ambient and 3 conductors in conduit or cable:
60° wire #3 AWG, 75°C or 90°C wire #4 AWG.

For higher ambient temperatures, or more than 3 conductors in a conduit or cable, additional factors apply, which may require larger sizes.

Refer BS7671-May be 16mm^2 for short run up to starter and 6mm^2 from starter to motor.

As in your question For 30 kw motor , line current 64A . For star delta , six number of cables requires from starter to motor . So current in each cable will be 64/1.732=~35A . So if you use AL CABLE ,then cable size will be 35 sq mm . For copper 16 sq mm . Above cable sizes are applicable up to 50m distance.

→British Standard 7671.

Any qualified local Electrician can sort that out. Open a dialogue. Telephone?