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Two generators 200∠30° and 210∠50° V

Short answer

Using per-phase values, I from G1 to G2 is 8.716 angle -133.84 A. Three-phase totals: G1 consumes 5.02 kW and generates 1.46 kvar; G2 generates 5.48 kW and 0.37 kvar; the line absorbs 0.46 kW and 1.82 kvar. Real power flows from G2 to G1.

Two 3-phase synchronous generators connected in star with neutral grounded are connected to each other through a line with series impedance per phase of 2 + j8 Ω. The terminal voltages of generators 1 and 2 are 200∠30° V and 210∠50° V respectively. Determine the active and reactive power generated/consumed by each generator.

The given terminal voltages are taken as per-phase (line-to-neutral) values, since the generators are star connected with neutral grounded and the impedance is per phase. Three-phase power is 3 times the per-phase power.

Let I flow from G1 to G2 through Z=2+j8 ΩZ = 2 + j8\ \Omega. Then S1=V1I∗S_1 = V_1I^* is the power delivered by G1 and S2=V2I∗S_2 = V_2I^* is the power received by G2.

Current

V1=200∠30∘=173.21+j100.00 VV2=210∠50∘=134.99+j160.87 VI=V1−V2Z=38.22−j60.872+j8=−6.037−j6.287=8.716∠−133.84∘ A\begin{aligned} V_1 &= 200\angle30^\circ = 173.21 + j100.00\ \text{V}\\ V_2 &= 210\angle50^\circ = 134.99 + j160.87\ \text{V}\\ I &= \frac{V_1 - V_2}{Z} = \frac{38.22 - j60.87}{2 + j8}\\ &= -6.037 - j6.287 = 8.716\angle-133.84^\circ\ \text{A} \end{aligned}

Powers per phase

S1=V1I∗=(200∠30∘)(8.716∠133.84∘)=−1674.31+j485.19 VAS2=V2I∗=(210∠50∘)(8.716∠133.84∘)=−1826.24−j122.55 VASline=∣I∣2Z=75.97(2+j8)=151.94+j607.74 VA\begin{aligned} S_1 &= V_1I^* = (200\angle30^\circ)(8.716\angle133.84^\circ) = -1674.31 + j485.19\ \text{VA}\\ S_2 &= V_2I^* = (210\angle50^\circ)(8.716\angle133.84^\circ) = -1826.24 - j122.55\ \text{VA}\\ S_{line} &= |I|^2Z = 75.97(2 + j8) = 151.94 + j607.74\ \text{VA} \end{aligned}

Interpretation

QuantityPer phaseThree-phase
G1 real powerconsumes 1674.31 W (motoring)consumes 5022.92 W
G1 reactive powergenerates 485.19 vargenerates 1455.57 var
G2 real powergenerates 1826.24 Wgenerates 5478.73 W
G2 reactive powergenerates 122.55 vargenerates 367.66 var
Line loss151.94 W, 607.74 var455.81 W, 1823.23 var

Check: 1826.24−1674.31=151.931826.24 - 1674.31 = 151.93 W and 485.19+122.55=607.74485.19 + 122.55 = 607.74 var.

Real power flows from G2 to G1 because V2V_2 leads V1V_1 by 20°. G1 behaves as a synchronous motor. Both machines supply reactive power, which is consumed by the line reactance.

Answer: G2 generates 5.48 kW and 0.37 kvar. G1 absorbs 5.02 kW (motor) and generates 1.46 kvar. The line absorbs 0.46 kW and 1.82 kvar (three-phase totals).

✓ Answer checked by Claude Opus 5.5 (high effort)

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