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The three-bus power system shown in the figure has one alternator connected to bus 2 which supplies 200 MW and 40 MVAR power. Bus 3 is infinite bus having a voltage of magnitude |V3| = 1.0 p.u. and angle of -15°. A variable current source, |I|∠φ is connected at bus 1 and controlled such that the magnitude of the bus 1 voltage is maintained at 1.05 p.u. and the phase angle of the source current φ = θ ± π/2, where θ is the phase angle of the bus 1 voltage. The three buses can be categorized for load flow analysis as

1. Bus 1 Slack bus Bus 2 P - |V| bus Bus 3 P - Q bus
2. Bus 1 P - |V| bus Bus 2 P - |V| bus Bus 3 Slack bus
3. Bus 1 P - Q bus Bus 2 P - Q bus Bus 3 Slack bus
4. Bus 1 P - |V| bus Bus 2 P - Q bus Bus 3 Slack bus

Correct answer: Bus 1 P - |V| bus Bus 2 P - Q bus Bus 3 Slack bus

Solution

Bus 1 is a P - |V| bus because it maintains a constant voltage magnitude while allowing the active power to vary. Bus 2 is a P - Q bus as it can absorb or supply both active and reactive power, and Bus 3 is the slack bus, which balances the system by providing the necessary power to maintain the overall power flow.

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