How to wire star-delta motor starter

Most induction motors are started directly on line, but when very large motors are started that way, they cause a disturbance of voltage on the supply lines due to large starting current surges.

To limit the starting current surge, large induction motors are started at reduced voltage and then have full supply voltage reconnected when they run up to near rotated speed.

this Short video showing how to wire start-delta motor starter. Star-delta starter control diagram. More electrical tips and diagrams