Basic AC Power THREE-PHASE CIRCUITSSolution:1. VL3 Vf(1.73)(240)VL415.2 volts2. PT3 VLILcosq(1.73)(415.2)(100)(0.9)PT64.6 kW3. QT3 VLILsinq(1.73)(415.2)(100)(0.436)QT31.3 kVAR4. ST3 VLIL(1.73)(415.2)(100)ST71.8 kVAUnbalanced3f LoadsAn important property of a three-phase balanced system is that the phasor sum of the three lineor phase voltages is zero, and the phasor sum of the three line or phase currents is zero. Whenthe three load impedances are not equal to one another, the phasor sums and the neutral current(In) are not zero, and the load is, therefore, unbalanced. The imbalance occurs when an open orshort circuit appears at the load.If a three-phase system has an unbalanced load and an unbalanced power source, the methodsof fixing the system are complex. Therefore, we will only consider an unbalanced load with abalanced power source.Example: A 3f balanced system, as shown in Figure 16a, contains a wye load. The line-to- linevoltage is 240V, and the resistance is 40 W in each branch.Rev. 0 Page 23 ES-09
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