How is speed increased in a Wound Rotor Motor?

In a Wound Rotor Motor, speed can be increased by shorting across the resistors. This method changes the rotor's resistance during operation. When the rotor is initially started, resistors are connected to provide high resistance, which limits the current and allows for controlled acceleration of the motor. As the motor reaches a certain speed, the resistors can be bypassed or shorted, reducing the resistance in the rotor circuit. This results in an increase in rotor current and consequently the speed of the rotor, leading to a higher overall speed of the motor.

In this context, adding more resistors would not enhance speed and could actually impede performance by increasing resistance further. Using a variable frequency drive, while a valid method for controlling motor speed, is more applicable to induction motors rather than directly applicable to controlling speed in a wound rotor motor using its inherent characteristics. Changing the rotor windings might alter motor characteristics or performance but is not a practical approach to simply increase speed during normal operations. Thus, shorting across the resistors is the most direct and effective method to achieve increased speed in a wound rotor motor system.