Secondary Resistance Starters

They can either be metal(nickel chrome compound) or liquid(water with salts added)

The greater part of the rotor winding is surrounded by iron so the rotor circuit is highly inductive. At starting, the rotor frequency is equal to the stator frequency, and so the reactance is great compared with the resistance. The rotor current therefore lags the rotor e.m.f by a large angle, the power factor is low and consequently the torque is small

An increase of the rotor circuit resistance will increase the impedance, and less current will flow in the rotor. The effect of the improved power factor predominates, and the starting torque is increased with secondary resistance, the starting torque can therefore be higher than that obtained with no resistance in the circuit