The GATE Grind

GATE 2014 EE (EE1) – Question 25

Power Systems · Principles of over-current, differential, directional and distance protection; Circuit breakers · 1 mark · Multiple choice

A three-phase-to-ground fault occurs at F₁ or F₂ in the system shown. Bus-A voltages and marked currents for these cases are V_F1,I_F1 and V_F2,I_F2. Which relation holds?

Diagram for GATE 2014 EE (EE1) question 25
  1. V_F1 leads I_F1 and V_F2 leads I_F2
  2. V_F1 leads I_F1 and V_F2 lags I_F2
  3. V_F1 lags I_F1 and V_F2 leads I_F2
  4. V_F1 lags I_F1 and V_F2 lags I_F2

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (C) V_F1 lags I_F1 and V_F2 leads I_F2

Explanation

For the forward fault F2, the line segment from Ato the fault is inductive, so VA=jXIF2and voltage leads the marked rightward current. For reverse fault F1, current from Ato the fault flows opposite the marked rightward IF1, giving VA=−jXIF1and voltage lags that marked current. Thus **VF1lags IF1and VF2leads IF2,C**.