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Three-Phase Systems in Power Applications problems


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

  • Options
  • A. 0 V
  • B. 90 V
  • C. 156 V
  • D. 180 V
  • Discuss
  • 2. A three-phase △-connected generator is driving a balanced load such that each phase current is 12 A in magnitude. When I ?a = 12 ∠30° A, what are the polar expressions for the other phase currents?

  • Options
  • A. I ?b = 12 ∠150° A, I ?c = 12∠?90° A
  • B. I ?b = 12∠120° A, I ?c = 12∠30° A
  • C. I ?b = 12∠30° A, I ?c = 12∠120° A
  • D. I ?b = 12∠90° A, I ?c = 12∠90° A
  • Discuss
  • 3. In a △-connected generator, all of the phase voltages are

  • Options
  • A. zero
  • B. equal in magnitude
  • C. one-third of total
  • D. one-sixth of total
  • Discuss
  • 4. In a certain three-wire Y-connected generator, the phase voltages are 2 kV. The magnitudes of the line voltages are

  • Options
  • A. 2,000 V
  • B. 6,000 V
  • C. 666 V
  • D. 3,464 V
  • Discuss
  • 5. The most common type of ac motor is the

  • Options
  • A. single-phase induction motor
  • B. two-phase induction motor
  • C. three-phase induction motor
  • D. two-phase squirrel-cage motor
  • Discuss
  • 6. In a three-phase system, when the loads are perfectly balanced, the neutral current is

  • Options
  • A. zero
  • B. one-third of maximum
  • C. two-thirds of maximum
  • D. at maximum
  • Discuss
  • 7. In a △-connected source feeding a Y-connected load,

  • Options
  • 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
  • Discuss
  • 8. In a balanced three-phase load, each phase has

  • Options
  • 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
  • Discuss
  • 9. In a Y-connected circuit, the magnitude of each line current is

  • Options
  • A. one-third the phase current
  • B. three times the corresponding phase current
  • C. equal to the corresponding phase current
  • D. zero
  • Discuss
  • 10. Polyphase generators produce simultaneous multiple sinusoidal voltages that are separated by

  • Options
  • A. certain constant phase angles
  • B. certain constant frequencies
  • C. certain constant voltages
  • D. certain constant currents
  • Discuss

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