ROTOR RESISTANCE STARTERS
o The easiest method of starting wound rotor (slip-ring) induction motors is to connect some extra resistance in the rotor circuit as shown in fig.
o Connection of extra resistance in the rotor circuit decreases the starting current and at the same time increases the starting torque.
o As the motor starts rotating the extra resistance is gradually cut out.
o When the motor attains rated speed the resistance is fully cut out.
When the motor attains rated speed the resistance is fully cut out and the slip ring terminals are short circuited.
The motor now operates on its own characteristics which give rise to maximum torque at a low slip.