Normally starting current of an induction motor is 6 to 7 times of the full load current. This is due to high
inertia of the rotor which draws more current require to move the rotor. So if a resistance is inserted in series with the circuit. For controlling inrush currents for starting only the resistance is gradually reduced. This would reduce the starting current.

There are a few types of starters for AC motor applications:
1. Rotor resistance starter - Is used only for slip rings
in squirrel cage wound rotors so external
resistance cant be added. In starting resistances are included to limit
the starting current.
2. Star delta starter-at the time starting the rotor is
connected as star and while it is in operation it switches to a delta connection.
It can be used for both slip and Squirrel cage IM.
3. Auto transformer starter- at the time starting by using an
auto transformer to reduce the initial voltage.
4. DOL (direct on line) starter - which doesnt reduce any staring current but
connects the motor terminals directly to the power supply.