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Three Phase system in Power Application
1.In a three-phase system, when the loads are perfectly balanced, the neutral
current is
A.
zero
B.
one-third of maximum
C.
two-thirds of maximum
D.
at maximum
2.In a -connected source driving a -connected load, the
A. load voltage and line voltage are one-third the source voltage for a given
phase
B. load voltage and line voltage are two-thirds the source voltage for a given
phase
C. load voltage and line voltage cancel for a given phase
D. load voltage, line voltage, and source phase voltage are all equal for a given
phase
3.In a certain three-wire Y-connected generator, the phase voltages are 2 kV.
The magnitudes of the line voltages are
A.
2,000 V
B.
6,000 V
C.
666 V
D.
3,464 V
4.In a -connected source feeding a Y-connected load,
A.
each phase voltage equals the difference of the corresponding load
voltages
B.
each phase voltage equals the corresponding load voltage
C.
each phase voltage is one-third the corresponding load voltage
D.
each phase voltage is 60° out of phase with the corresponding load
voltage
5.In a Y-Y source/load configuration, the
A. phase current, the line current, and the load current are all equal in each
phase
B. phase current, the line current, and the load current are 120° out of phase
C. phase current and the line current are in phase, and both are 120° out of
phase with the load current
D. line current and the load current are in phase, and both are out of phase with
the phase current
6.
A.
B.
C.
D.
In a Y-connected circuit, the magnitude of each line current is
one-third the phase current
three times the corresponding phase current
equal to the corresponding phase current
zero
7.
A.
B.
C.
D.
A constant load power means a uniform conversion of
mechanical to electrical energy
electrical to mechanical energy
current to voltage
voltage to current
8.
A two-phase generator is connected to two 90 load resistors. Each coil
generates 120 V ac. A common neutral line exists. How much current flows
through the common neutral line?
A.
1.33 A
B.
1.88 A
C.
2.66 A
D.
1.77 A
9.
A single-phase sinusoidal voltage of 120 V is connected to a 90 load.
Current in the circuit is
A.
13.3 mA
B.
133 mA
C.
1.33 A
D.
6.2 A
10.
A three-phase generator is connected to three 90 load resistors. Each coil
generates 120 V ac. A common neutral line exists. How much current flows
through the common neutral line?
A.
0A
B.
1.33 A
C.
3.99 A
D.
2.66 A
11.
Compare the total copper cross sections in terms of current-carrying
capacity for a single-phase and a three-phase 120 V system with effective load
resistance of 15 .
A.
single-phase 32 A; three-phase 16 A
B.
single-phase 16 A; three-phase 8 A
C.
single-phase 8 A; three-phase 4 A
D.
single-phase 16 A; three-phase 0 A
12.
If in a Y-connected ac generator, each phase voltage has a magnitude of
90 VRMS, what is the magnitude of each line voltage?
A.
0V
B.
90 V
C.
156 V
D.
180 V
13.
A.
B.
C.
D.
Referring to Problem 3, the total copper cross section must handle
1.33 A
2.66 A
266 mA
26.6 mA
14.
Polyphase generators produce simultaneous multiple sinusoidal voltages
that are separated by
A.
certain constant phase angles
B.
certain constant frequencies
C.
certain constant voltages
D.
certain constant currents
15.
A.
B.
C.
D.
In a balanced three-phase load, each phase has
an equal amount of power
one-third of total power
two-thirds of total power
a power consumption equal to IL
16.
In a certain Y-Y system, the source phase currents each have a
magnitude of 9 A. The magnitude of each load current for a balanced load
condition is
A.
3A
B.
6A
C.
9A
D.
27 A
17.
A three-phase -connected generator is driving a balanced load such that
each phase current is 12 A in magnitude. When I θa = 12 30° A, what are the
polar expressions for the other phase currents?
A.
B.
C.
D.
I θb = 12 150° A, I θc = 12–90° A
I θb = 12120° A, I θc = 1230° A
I θb = 1230° A, I θc = 12120° A
I θb = 1290° A, I θc = 1290° A
18.
In a Y-connected circuit, between each line voltage and the nearest phase
voltage, there is a phase angle of
A.
0°
B.
30°
C.
60° D.
120°
19.
A.
B.
C.
D.
The most common type of ac motor is the
single-phase induction motor
two-phase induction motor
three-phase induction motor
two-phase squirrel-cage motor
20.
A.
B.
C.
D.
In a Y-connected source feeding a -connected load,
each phase of the load has one-third of the full line voltage across it
each phase of the load has two-thirds of the full line voltage across it
each phase of the load has the full line voltage across it
each phase of the load has a voltage across it equal to
21.
A.
B.
C.
D.
In a -connected generator, all of the phase voltages are
zero
equal in magnitude
one-third of total
one-sixth of total