# 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

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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 $1.0\;pu$ is . 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 ________.

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Voltage at bus B after 3 – phase fault at A  $= 0.8\;p.u.$

$\begin{array}{l} {V_B}\; = \;V\left( {prefault} \right)\;-\;{Z_{12}}\; \times \;{I_{f\left( B \right)}}\\ 0.8\; = \;1.0\;-\;{Z_{12}}\; \times \;10\\ {Z_{12}}\; = \;0.02\;p.u.\\ {V_A}\; = \;1.0\;-\;\left( {0.02\; \times \;8} \right)\\ {V_A}\; = \;0.84\;p.u \end{array}$

Note:

For the voltage magnitude at bus B during a three-phase fault at bus A. So we use fault current of bus A

For the voltage magnitude at bus A during a three-phase fault at bus B. So we use fault current of bus B