The rotor slip rings connect to start-up resistorsin order to provide current and speed control onstart-up.• When the motor is started, the frequency of currentflowing through the rotor windings is nearly 60 Hz.• Once up to full speed, the rotor current frequencydrops down below 10 Hz to nearly a DC signal.• The motor is normally started with full externalresistance in the rotor circuit that is graduallyreduced to zero, either manually or automatically.• This results in a very high starting torque from zerospeed to full speed at a relatively low starting current.• With zero external resistance, the wound-rotormotor characteristics approach those of the squirrelcage motor.• Interchanging any two stator voltage supply leadsreverses the direction of rotation.
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