2.21 The three-phase source line-to-neutral voltages are given by E= 10/0, E = 10/+240, and E = 10/-240 volts. Is the source balanced? (a) Yes (b) No
2.21 The three-phase source line-to-neutral voltages are given by E= 10/0, E = 10/+240, and E = 10/-240 volts. Is the source balanced? (a) Yes (b) No
Power System Analysis and Design (MindTap Course List)
6th Edition
ISBN:9781305632134
Author:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma
Publisher:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma
Chapter2: Fundamentals
Section: Chapter Questions
Problem 2.52P: A balanced three-phase load is connected to a 4.16-kV, three-phase, fourwire, grounded-wye dedicated...
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Question
Transcribed Image Text:2.21
The three-phase source line-to-neutral voltages are given by
E = 10/0°, Em = 10/+240°, and En = 10/-240 volts.
Is the source balanced?
(a) Yes
(b) No
In a balanced 3-phase wye-connected system with positive-sequence source, the line-
to-line voltages are v3 times the line-to-neutral voltages and lend by 30.
(a) True
2.22
(b) False
2.23 In a balanced system, the phasor sum of line-to-line voltages and the phasor sum of
line-to-neutral voltages are always equal to zero.
(a) False
(b) True
2.24 Consider a three-phase Yconnected source feeding a balanced-Y load. The phasor
sum of the line currents as well as the neutral current are always zero.
(b) False
(a) True
2.25
For a balanced-A load supplied by a balanced positive-sequence source, the line cur-
rents into the load are v3 times the A-load currents and lag by 30°.
(a) True
A balanced A-load can be converted to an equivalent balanced-Y load by dividing the
A-load impedance by
(a) V3
When working with balanced three-phase circuits, per-phase analysis is commonly
done after converting A loads to Y loads, thereby solving only one phase of the
circuit.
(b) False
2.26
) з
(e) 1/3
2.27
(a) True
(b) False
2.28 The total instantaneous power delivered by a three-phase generator under balanced
operating conditions is
(a) a function of time
(b) a constant
2.29 The total instantaneous power absorbed by a three-phase motor (under balanced
steady-state conditions) as well as a balanced three-phase impedance load is
(a) a constant
(b) a function of time
2.30
Under balanced operating conditions, consider the 3-phase complex power delivered
by the 3-phase source to the 3-phase load. Match the following expressions, those on
the left to those on the right.
0) Real power, Py
(ii) Reactive power, Qu
(ii) Total apparent power Sy
(iv) Complex power, Sy
(a) (V3 VLL. IL)VA
(b) (V3 Vu sng) var
(e) (V3 VLL. IL cos ø) W
(d) Py +Qy
Note that VLL is the rms line-to-line voltage, IL is the ms line current, and o is the
power-factor angle.
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