In delta connection the full line voltage is applied to each of the three motor windings. This maximizes the current through each winding and therefore the torque. read more
But, the motor operating voltage is 220v 3 phase, you can only connect on star if input voltage available is 415v 3 phase, but available input 220v 3 phase voltage motor operating voltage 220v 3 phase, delta connection is fine. read more