A schematic diagram of an alternator is shown below where Van = Vbn = Vcn = V1. If a single phase to ground fault occurs at location 'a', what will be the voltage at 'b' and 'c'? [Figure description: A star-connected three-phase alternator armature: three winding coils connect terminals a, b and c to a common neutral point n (Y connection). Terminal a is connected to line R, terminal b to line Y and terminal c to line B. A separate field winding with a DC battery is drawn to the left (rotor excitation).]
- A. Vbn = Vcn = √3 V1
- B. Vbn = Vcn = V1
- C. Vbn = Vcn = 0
- D. None of the above
Answer: A. Vbn = Vcn = √3 V1
Explanation: In an ungrounded system, a single-phase-to-ground fault on phase a shifts the neutral potential, raising the healthy line-to-ground voltages to full line-to-line value: Vbn = Vcn = √3 V1.