EENG20005 - Electrical Energy Conversion and Supply
Example Sheet 3 - Three-Phase Systems
1. A four-wire star connected load is supplied from a three-phase source. The source voltages to neutral are designated vAN, vBN and vCN. If the load is balanced, show that the current in the neutral conductor is zero.
2. A four-wire star connected load is supplied from a three-phase source. The source voltages to neutral are designated vAN, vBN and vCN and the phase sequence is positive. The load is unbalanced and the corresponding impedances are given by:
ZA = 10 ∠0° Ω
ZB = 12 ∠ − 30° Ω
ZC = 9 ∠ − 40° Ω
If the supply voltage is 346V, calculate the current in the neutral conductor. Give the answer in polar form. with the phase angle referenced to vAN.
3. A delta-connected three-phase load is connected to terminals A, B and C. The load impedances are all resistive and are given by:
RAB = 50 Ω
RBC = 30 Ω
RCA = 65 Ω
Find the three resistances, RA, RB and RC in the equivalent star-connected load.
4. A delta-connected three-phase load is connected to terminals A, B and C. It is
energised from a star-connected generator. The source voltages are designated vAN, vBN and vCN with respect to the generator’s star point and the phase sequence is positive. The load is unbalanced and the corresponding impedances are given by:
ZAB = 25 ∠ − 35° Ω
ZBC = 17 ∠0° Ω
Z CA = 30 ∠ − 20° Ω
If the supply voltage is 380V, calculate the currents in each of the three load impedances. Give the answers in polar form. with the phase angles referenced to vAN.