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Observe the 3-bus network. Bus 1 is the slack bus (V = 1.05 pu, θ = 0°) — it balances any power mismatch. Bus 2 is a PV generator bus (P = 50 MW, V = 1.04 pu). Bus 3 is the load bus (100 MW + 50 MVAr).
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The slack bus acts like an infinite busbar. Its voltage is fixed; its active power output adjusts to cover all generation-load-loss imbalances.
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Click 'Run Power Flow'. The Newton-Raphson solver will iterate to convergence. Check the iteration count and maximum mismatch in the status bar. NR typically converges in 3–6 iterations for well-conditioned networks.
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The solver forms a Jacobian matrix (∂P/∂θ, ∂P/∂V, ∂Q/∂θ, ∂Q/∂V) at each step and solves a linear system to update voltages.
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Click on Bus 3 to open the Bus Inspector. Note its voltage magnitude. Is it above or below 1.0 pu? Voltage drops occur along the line due to line impedance × current. The reactive load (50 MVAr) exacerbates the drop.
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The voltage magnitude at Bus 3 should be below the source voltages (1.05, 1.04 pu) due to resistive and reactive voltage drop.
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Click on the line L1-2. Check its thermal loading percentage. A high loading means the line is operating close to its thermal limit (200 MVA rating for this line).
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Line loading = S_flow / S_rating × 100%. Overloaded lines cause thermal damage and can lead to line trips.
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Observe the Voltage Profile chart. All buses should be within the green zone (0.95–1.05 pu). If Bus 3 is in the orange or red zone, the network has a voltage violation that would require corrective action (e.g. reactive compensation or tap-changer adjustment).
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UK Grid Code requires transmission voltages within ±5% of nominal in normal operating conditions.