Description
Question 1:
A balanced Y-connected voltage source with a phase voltage �!” = 277∠0°� delivers to a
balanced delta connected load with impedance �#$%&! = 45 − �18Ω that is in parallel with a Yconnected load with impedance �’ = 30 + �15Ω.
(a) Calculate the total current deliver to the loads
(b) Calculate the total real and reactive power for the loads
Question 2:
Consider the three-phase system in Figure 1. From the generator bus (marked as B1) power is
delivered to a load of 150MW and 60Mvar at bus 3 and a load of 120MW and 60Mvar at bus 4
(all values in 3-Phase). The line voltage magnitude at bus 4 (B4) for load 2 needs is kept at 69
kV.
(a) Find the per-unit representation of the system with a power base value of:
• Option one: single-phase value of 100MVA for the power and phase voltage base
value of 23/ √3 kV at bus B1
• Option two: three-phase value of 300MVA for the power and line voltage
base value of 23 kV at bus B1
Per the option you chose:
1. Find the base values for the systems in figure 1
2. Find all per-unit line impedances: transformers T1 and T2 impedances
3. Find all per-unit values for all given powers, impedances, and voltages
(b) What is the line voltage magnitude at the generating source at bus 1 (magnitude of the
line voltage at B1)?
(c) Find the real and reactive power for the generator (remember, it’s a three phase system).
332:494/599– HW Set 2 2
Figure 1(a): one line diagram for system in question 2
Figure 1(b): one-line diagram for system in question 2 in per-unit
Question 3:
The three-phase power and line-line voltage. are given for the electric power system in
figure 2. For the per-unit analysis, a base value of 100MVA is chosen for the three-phase
power and a base value of 20kV is chosen for the line voltage on generator 1 end.
(a) Find the base values for the systems in figure 2
(a) Find all per-unit line impedances: transformers T1 and T2 impedances; generators
G1 and G2 impedances.
(b) Find all per-unit values for all given powers, and voltages
(c) Find load1 impedance
(d) Find the current flow through the load
332:494/599– HW Set 2 3
Figure 2 (a): one-line diagram for system in question 3
Figure 2 (b): one-line diagram for system in question 3 in per-unit
Figure 2 (c): OR another representation… one-line diagram for system in
question 3 in per-unit
