Electrical Engineering MCQ
The resistance and reactance of a line are found to be equal and regulation is zero, then load will have:
- Zero power factor
- 0.707 lagging power factor
- 0.707 leading power factor
- Unity power factor
Correct answer: 3. 0.707 leading power factor
Explanation: The analysis you provided is accurate. If the resistance and reactance of a line are equal, and the voltage regulation is zero, it implies a condition where the power factor is 0.707 leading. This is because the cosine of the angle (φ) between voltage and current (cosφ) in this scenario is equal to 1/√2 or approximately 0.707, indicating a leading power factor.
Voltage regulation= (Vs – Vr)/Vr = Ir(R cosφ ± X sinφ)/Vr
For lagging load:
Voltage regulation = Ir(R cosφ + X sinφ)/Vr
For leading load:
Voltage regulation = Ir(R cosφ – X sinφ)/Vr
For unity load power factor:
Voltage regulation = Ir(R cosφ)/Vr
Therefore, zero voltage regulation is possible only for leading power factor.
From given data
Cosφ = X/Z = 1/√2 = 0.707 leading