How to start 220/380V 3 phases induction motor by star-delta method with 3 phases 380V power source?
That's simple. First the motor is wired in star (Y) and the voltage is distributed over two windings. Each winding gets Vline/sqrt(3) if you calculate from 380V you get 220V. The current is also reduced by factor 1/sqrt(3), while the power is reduced by factor 1/sqrt(3)*sqrt(3) = 1/3.
Once the motor reaches the rpms, it is switched to delta connection, now you get full voltage on windings, current and nominal power.