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EEE :: Three - Phase Systems in Power Applications

  1. 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?

  2. A.
    0 A
    B.
    1.33 A
    C.
    3.99 A
    D.
    2.66 A

  3. 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 .

  4. 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

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

  6. A.
    0 V
    B.
    90 V
    C.
    156 V
    D.
    180 V

  7. Polyphase generators produce simultaneous multiple sinusoidal voltages that are separated by

  8. A.
    certain constant phase angles
    B.
    certain constant frequencies
    C.
    certain constant voltages
    D.
    certain constant currents

  9. In a balanced three-phase load, each phase has

  10. A.
    an equal amount of power
    B.
    one-third of total power
    C.
    two-thirds of total power
    D.
    a power consumption equal to IL

  11. 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

  12. A.
    3 A
    B.
    6 A
    C.
    9 A
    D.
    27 A

  13. 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?

  14. A.
    I θb = 12 150° A, I θc = 12–90° A
    B.
    I θb = 12120° A, I θc = 1230° A
    C.
    I θb = 1230° A, I θc = 12120° A
    D.
    I θb = 1290° A, I θc = 1290° A

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

  16. A.
    B.
    30°
    C.
    60°
    D.
    120°

  17. The most common type of ac motor is the

  18. A.
    single-phase induction motor
    B.
    two-phase induction motor
    C.
    three-phase induction motor
    D.
    two-phase squirrel-cage motor

  19. In a Y-connected source feeding a -connected load,

  20. A.
    each phase of the load has one-third of the full line voltage across it
    B.
    each phase of the load has two-thirds of the full line voltage across it
    C.
    each phase of the load has the full line voltage across it
    D.
    each phase of the load has a voltage across it equal to