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Line power loss, 138.5∠8° kV and 132 kV

Short answer

Active power loss is 9.12 MW and reactive loss is −9.60 MVAr, meaning the line is a net source of 9.60 MVAr. This occurs because the line's shunt capacitive generation exceeds its series inductive absorption.

For a 3-phase overhead line, the following data is available: VS,L = 138.5∠8° kV, VR,L = 132∠0° kV, A = 0.983∠0.68°, B = 36.5∠71.5° Ω. Determine the transmission line active and reactive power loss.

Use the power-circle equations (with D=AD = A). Line voltages in kV give three-phase MW and MVAr.

Data: ∣VS∣=138.5|V_S| = 138.5 kV, ∣VR∣=132|V_R| = 132 kV, δ=8∘\delta = 8^\circ, ∣A∣=0.983|A| = 0.983, α=0.68∘\alpha = 0.68^\circ, ∣B∣=36.5 Ω|B| = 36.5\ \Omega, β=71.5∘\beta = 71.5^\circ.

Constants

∣VS∣∣VR∣∣B∣=138.5×13236.5=500.88∣A∣∣VR∣2∣B∣=0.983×132236.5=469.25∣A∣∣VS∣2∣B∣=0.983×138.5236.5=516.61\begin{aligned} \frac{|V_S||V_R|}{|B|} &= \frac{138.5\times132}{36.5} = 500.88 \\ \frac{|A||V_R|^2}{|B|} &= \frac{0.983\times132^2}{36.5} = 469.25 \\ \frac{|A||V_S|^2}{|B|} &= \frac{0.983\times138.5^2}{36.5} = 516.61 \end{aligned}

Angles: β−δ=63.5∘\beta-\delta = 63.5^\circ, β−α=70.82∘\beta-\alpha = 70.82^\circ, β+δ=79.5∘\beta+\delta = 79.5^\circ.

Receiving end

PR=500.88cos⁡63.5∘−469.25cos⁡70.82∘=223.49−154.17=69.32 MWQR=500.88sin⁡63.5∘−469.25sin⁡70.82∘=448.25−443.21=5.05 MVAr\begin{aligned} P_R &= 500.88\cos63.5^\circ - 469.25\cos70.82^\circ = 223.49 - 154.17 = 69.32\ \text{MW} \\ Q_R &= 500.88\sin63.5^\circ - 469.25\sin70.82^\circ = 448.25 - 443.21 = 5.05\ \text{MVAr} \end{aligned}

Sending end

PS=516.61cos⁡70.82∘−500.88cos⁡79.5∘=169.72−91.28=78.45 MWQS=516.61sin⁡70.82∘−500.88sin⁡79.5∘=487.93−492.49=−4.56 MVAr\begin{aligned} P_S &= 516.61\cos70.82^\circ - 500.88\cos79.5^\circ = 169.72 - 91.28 = 78.45\ \text{MW} \\ Q_S &= 516.61\sin70.82^\circ - 500.88\sin79.5^\circ = 487.93 - 492.49 = -4.56\ \text{MVAr} \end{aligned}

Losses

Ploss=PS−PR=78.45−69.32=9.12 MWQloss=QS−QR=−4.56−5.05=−9.60 MVAr\begin{aligned} P_{loss} &= P_S - P_R = 78.45 - 69.32 = 9.12\ \text{MW} \\ Q_{loss} &= Q_S - Q_R = -4.56 - 5.05 = -9.60\ \text{MVAr} \end{aligned}

The negative reactive "loss" means the line generates about 9.6 MVAr net (its shunt charging exceeds the I2XI^2X absorbed in its series reactance).

Answer: Active power loss ≈ 9.12 MW; reactive power loss ≈ −9.60 MVAr (line is a net source of 9.60 MVAr).

✓ Answer checked by Claude Opus 5.5 (high effort)

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