Question

A synchronous phase modifier as compared to the synchronous motor used for mechanical loads has
1. Larger shaft and higher speed
2. Smaller shaft and higher speed
3. Larger shaft and lower speed
4. Smaller shaft and lower speed

Answer 1

Correct Answer - Option 2 : Smaller shaft and higher speed

Concept:

Synchronous Phase Modifier:

• It is nothing but an over-excited synchronous motor running without a mechanical load.
• It is provided with means for varying its power factor to simulate a capacitive or inductive reactor.
• It is used in voltage regulation of alternating-current power systems.

 

Explanation:

A synchronous motor can be made to take either a lagging or leading current from the line by alternating its excitation. Idle running synchronous motors are used in connection with power plants to correct for the low power factor of the load and thus reduced the current and power losses in the feeders and generators.

Synchronous phase modifier differ from the ordinary synchronous motor is as much as they are built for the highest economical speeds and provided with smaller shafts and bearings.