Motor Torque

The torque will be 1/3 of rated torque as applied voltage becomes 58% of rated voltage.

You Mean 2/3rd of the rated torque ?

No since maximum power that can be delivered is 1/3rd.

Hence maximum load (torque) - assuming the minor change in rpm (slip) as negligible would be 1/3rd

Actual torque however as PWS said is depending on the load, and the power, rpm and thereby torque would be detrmined by the intersecting points of the OCCs.

He may have meant rated torque in star as a fraction of rated torque in delta. Starting torque in star is 2/3 (approx) of rated torque in delta.

It is the shaft mechanical load that determines the torque, not the motor.

Do you mean the same voltage in each case, as in a star-delta starter? In that case, the full-load torque (and power) in star are about 1/3 of values in delta. Perhaps rather less, as according to data I have the current falls by more than the voltage, and torque varies as current². So as voltage is down by 1/√3 = 0.577, current down by say 0.5, and torque by 0.5² = 0.25. As the starting torque in delta is about 2 x full-load torque, starting torque in star is about 2 x 0.25 = 0.5 x value in delta.

But if you mean the supply voltage is correct for the connection type (so √3 x higher in star) torque and power are the same for both.

Torque varies as the square of the voltage. In Star, the effective voltage across each coil in the motor is now phase to neutral, so it is lower by the square root if 3, which means 1/1.732 or 58%. Peak torque from the motor then is .58 * .58 = .33, or 1/3 of what it was when connected in Delta. Keep in mind however that IEC dual voltage motors are designed so that you connect in Star if you have the higher voltage, Delta if you have the lower; i.e. 380V = Star connection, 220V = Delta connection. I'm too lazy right now to look up a 6 lead motor diagram to see if that applies here and you didn't bother to post all of the necessary information anyway.

380V star, 220V delta is no good if you want to use star-delta starting with the usual 380V supply. It has to be 380V delta (660V star).

The 6 terminals are connected the same whatever the voltages - for delta, bridge across in 3 pairs, and connect a supply phase to each pair. For star, bridge all 3 terminals in one row of 2, and connect supply to the other 3. Of course, for star-delta all terminals are connected separately, to 6 cable cores.

Do you mean starting torque or full load rated torque?