I was on the lookout for an old fan regulator. I had heard that its power consumption was constant at all speeds.
I could lay my hands on this 1970 regulator. It appears to be a transformer with rotary switch tap selection.
I am curious to know about its function especially with respect to the power consumption at different speeds.
The ceiling fan has a split-phase, capacitor-run motor with variable-voltage speed control.
Before thyristor control took over, series voltage-dropping resistors and, rarely, auto transformers were used for speed control.
This regulator comprises an autotransformer with taps and a tap selector switch to select the voltage and hence the speed.
The energy loss in the series voltage-dropping resistor type regulator is avoided with the autotransformer.
That is either an autotransformer or series inductor used to reduce the motor speed by reducing the voltage as explained in this question: Speed control for PSC induction motor. The mechanical the torque required to turn a fan is proportional to the square of the fan speed as shown by the red curve in my answer to the above question. Power is torque multiplied by speed, so the power required by a fan is proportional to the cube of the fan speed. So if the speed is reduced to 70%, the power is 0.7 cubed or 34 percent of the power required at full speed. However the efficiency of the motor is lower when the speed is reduced, so the electrical power saved is quite a bit less. However even the least efficient method of reducing fan speed is likely to save some power. Using an autotransformer or inductor to reduce the voltage is not the least efficient method.
