GATE 2016 EE – Question 30
The magnitude of three-phase fault currents at buses A and B of a power system are 10 pu and 8 pu, respectively. Neglect all resistances in the system and consider the pre-fault system to be unloaded. The pre-fault voltage at all buses in the system is 1.0 pu. The voltage magnitude at bus B during a three-phase fault at bus A is 0.8 pu. The voltage magnitude at bus A during a three-phase fault at bus B, in pu, is ________.
Practise this question in The GATE Grind →
Show answer and explanation
Correct answer: 0.83 to 0.85
Explanation
With a pre-fault voltage of 1 pu, the fault current at bus A is $\frac{1}{Z_{AA}} = 10$, so $Z_{AA} = 0.1$. Similarly $Z_{BB} = \frac{1}{8} = 0.125$. During a fault at A, the voltage at B is $1 - \frac{Z_{BA}}{Z_{AA}} = 0.8$, so $Z_{BA} = 0.02$. During a fault at B, the voltage at A is $1 - \frac{Z_{AB}}{Z_{BB}} = 1 - \frac{0.02}{0.125} = 0.84$ pu.