Questions: A motor is a three-phase motor that runs at a constant speed, independent of the load connected to it.

Solution Steps

To determine which motor runs at a constant speed independent of the load, we need to understand the characteristics of each motor type:

1. Squirrel-cage Motor: This is a type of induction motor. Its speed varies slightly with the load due to slip, which is the difference between synchronous speed and actual speed.

2. Wound-rotor Motor: Another type of induction motor, similar to the squirrel-cage motor, but with external resistors that can be adjusted. It also experiences slip, causing speed variation with load.

3. Synchronous Motor: This motor runs at a constant speed, which is the synchronous speed, regardless of the load. It is designed to operate at a speed that is synchronized with the frequency of the supply current.

4. Repulsion Motor: This is a type of single-phase motor that also experiences speed variation with load.

From the characteristics outlined, the synchronous motor is the only type that runs at a constant speed, independent of the load. This is because it operates at synchronous speed, which is determined by the power supply frequency and the number of poles in the motor.

Final Answer