A 3 phase synchronous motor, connected to an infinite bus, operating at a leading pf with a constant load torque, if excitation is increased (δ is load angle and φ power factor angle)
- A. Both δ and φ decreases
- B. δ and φ both increases
- C. δ increases but φ decreases
- D. δ decreases but φ Increases
Answer: C. δ increases but φ decreases
Explanation: When mechanical shaft load on a synchronous motor increases, the rotor is pulled backward relative to the stator field, increasing the torque angle δ while decreasing the power factor angle φ.