Home > Polyphase Systems in Power Applications > Multiple Choice >

 Polyphase Systems in Power Applications Multiple Choice

Choose the best response to complete the sentence or answer the question. You will need symbol font on your computer to see Greek symbols such as and .

1 .       Polyphase generators produce simultaneous multiple sinusoidal voltages that are separated by [Hint]

 certain constant phase angles certain constant frequencies certain constant voltages certain constant currents

2 .       The most common type of ac motor is the [Hint]

 single-phase induction motor two-phase induction motor three-phase induction motor two-phase squirrel-cage motor

3 .       A single-phase sinusoidal voltage of 120 V is connected to a 90 load. Current in the circuit is [Hint]

 13.3 mA 133 mA 1.33 A 6.2 A

4 .       Referring to Problem 3, power consumption is [Hint]

 16 W 160 mW 160 W 3,459 W

5 .       Referring to Problem 3, the total copper cross section must handle [Hint]

 1.33 A 2.66 A 266 mA 26.6 mA

6 .       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? [Hint]

 1.33 A 1.88 A 2.66 A 1.77 A

7 .       Referring to Problem 6, the total copper cross section must handle [Hint]

 1.33 A 2.66 A 1.88 A 4.54 A

8 .       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? [Hint]

 0 I 1.33 A 3.99 A 2.66 A

9 .       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 . [Hint]

 single-phase 32 A; three-phase 16 A single-phase 16 A; three-phase 8 A single-phase 8 A; three-phase 4 A single-phase 16 A; three-phase 0 A

10 .       A constant load power means a uniform conversion of [Hint]

 mechanical to electrical energy electrical to mechanical energy current to voltage voltage to current

11 .       In a three-phase system, the voltages are separated by [Hint]

 45° 90° 120° 180°

12 .       In a three-phase system, when the loads are perfectly balanced, the neutral current is [Hint]

 zero one-third of maximum two-thirds of maximum at maximum

13 .       In a Y-connected circuit, the magnitude of each line current is [Hint]

 one-third the phase current three times the corresponding phase current equal to the corresponding phase current zero

14 .       In a Y-connected circuit, between each line voltage and the nearest phase voltage, there is a phase angle of [Hint]

 0° 30° 60° 120°

15 .       If in a Y-connected ac generator, each phase voltage has a magnitude of 90 VRMS, what is the magnitude of each line voltage? [Hint]

 0 V 90 V 156 V 180 V

16 .       In a -connected generator, all of the phase voltages are [Hint]

 zero equal in magnitude one-third of total one-sixth of total

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? [Hint]

 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 certain three-wire Y-connected generator, the phase voltages are 2 kV. The magnitudes of the line voltages are [Hint]

 2,000 V 6,000 V 666 V 3,464 V

19 .       Referring to Problem 18, if all phase currents are 3 A, the line current magnitudes are [Hint]

 3 A 1 A 9 A 18 A

20 .       In a Y-Y source/load configuration, the [Hint]

 phase current, the line current, and the load current are all equal in each phase phase current, the line current, and the load current are 120° out of phase phase current and the line current are in phase, and both are 120° out of phase with the load current line current and the load current are in phase, and both are out of phase with the phase current

21 .       In a Y-connected source feeding a -connected load, [Hint]

 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

22 .       In a -connected source feeding a Y-connected load, [Hint]

 each phase voltage equals the difference of the corresponding load voltages each phase voltage equals the corresponding load voltage each phase voltage is one-third the corresponding load voltage each phase voltage is 60° out of phase with the corresponding load voltage

23 .       In a -connected source driving a -connected load, the [Hint]

 load voltage and line voltage are one-third the source voltage for a given phase load voltage and line voltage are two-thirds the source voltage for a given phase load voltage and line voltage cancel for a given phase load voltage, line voltage, and source phase voltage are all equal for a given phase

24 .       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 [Hint]

 3 A 6 A 9 A 27 A

25 .       In a balanced three-phase load, each phase has [Hint]

 an equal amount of power one-third of total power two-thirds of total power a power consumption equal to

 Copyright © 1995-2010, Pearson Education, Inc., publishing as Pearson Prentice Hall Legal and Privacy Terms