Synchronous Motors

Step 1: Observe the given phasor diagram.
In the phasor diagram, the terminal voltage is taken as the reference and is shown along the horizontal axis. The induced emf is shown leading the terminal voltage by an angle.
Step 2: Identify the operating mode (generator or motor).
For a synchronous machine connected to an infinite bus:
- If the induced emf leads the terminal voltage , the machine is operating as a synchronous generator.
- If the induced emf lags behind the terminal voltage , the machine operates as a synchronous motor.
Since is leading in the given diagram, the machine is acting as a generator.
Step 3: Determine the power factor nature.
In a synchronous generator:
- If the generator is over-excited, it supplies reactive power to the system and operates at a lagging power factor.
- If the generator is under-excited, it absorbs reactive power and operates at a leading power factor.
The given phasor diagram shows significantly leading , indicating an over-excited condition.
Step 4: Conclusion.
Hence, the synchronous machine is operating as a generator at lagging power factor.