induction motors?

For Example a 55kW, 400V, Delta-connected motor in 400V system can be started by Star-Delta starter, but a 55kW, 400V Star-connected motor can not be started by Star-Delta starter. in the latter case the phase windings of motor are not designed for Delta connection, because the voltage across each phase windings will be 400V, however the design value is 400/√3 i.e 230V.

In Star-connection, the motor torque will be 1/3 times of Delta-connection

In Star-connection, the motor current will be 1/3 times of Delta-connection, it is important in motor starting

If you take a fourrier transform from the motor current, then you can distribute the motor current in different "smaller" currents all with their own frequency and their own amplitude. We call these different currents "harmonics". For a 50Hz current you have harmonics from frequency 150Hz, 250Hz, 350Hz, etc.

These higher harmonics create additional loss in transformers and cables.

When a motor is connected in Delta, you can prove that the 3° harmonic (150 Hz) is eliminated in a three faze system.

Hugh motors need big currents so the harmonics will also be big equal as the higher harmonic losses.

Depending upon motor size and application, that may not be a correct assumption. In the refrigeration industry, small three-phase motors, up to about 30 horsepower (Yes, I am an American) would use a three-terminal motor wired internally as either a Wye or a Delta. Actually, most are wired in a Wye because it it can have a thermal overload built into the center connection point.

Larger motors are usually six-terminal part-wound motors. This type of motor connected to an external wye-delta starter can be started as a wye for low starting amps, then externally re-conneced to a delta, for high running power.