What does the adjustment of speed in a multispeed motor primarily depend on?

The adjustment of speed in a multispeed motor primarily depends on the field winding configuration. In such motors, the arrangement and characteristics of the field windings play a crucial role in determining the motor's operational speed. By altering the configuration of the field windings, different magnetic fields are created, which affects the overall performance and speed of the motor.

For instance, in a motor where multiple field winding sets are available, switching between these configurations can provide different speeds. This versatility allows for precise control over how the motor operates in various applications, making it possible to achieve desired speed settings effectively.

The other options, while factors that might influence motor operation under certain conditions, do not have the same direct impact on speed adjustment compared to the field winding configuration. Voltage supply refers to the power provided to the motor, which does affect performance but does not necessarily change the speed in a controlled way. Rotor speed is a direct result of the motor's operating conditions, and motor size, while affecting torque and overall performance, does not inherently dictate the motor's ability to achieve different speeds.