In a three-phase power system the phases of each voltage

Question

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In a three-phase power system, the phases of each voltage are normally separated by how many time degrees?

A. 120 B. 90 C. 180 D. 60

If a motor designed for 50 or 60 cycle operation is connected to 60 Hz current, the motor will

A. stall easily. B. overheat and fail. C. produce less torque. D. turn Faster If plotted, the voltage or current produced by an alternator forms a curve called a      A. sawtooth wave. B. sine wave. C. pulsed wave. D. hertz wave.

AC power is created by using

A. an AC motor B. an AC generator C. Transformers D. Batteries

In a modern industrial plant, the most likely polyphase power system in use is a

A. one-phase system. B. three-phase system. C. two-phase system. D. four-phase system.

What is the real power if Erms = 100 V, Irms= 2 A, and the circuit has a power factor of 0.8?

A. 40 W B. 80 W C. 250 W D. 160 W

The total number of AC cycles completed in one second is the current's

A. timing B. phase C. frequency D. alteration

8.   What is the real power (rounded) of a balanced, three-phase, Y-connected system that has a power factor of 0.9, an effective line current of 50 A and a phase voltage of 200 V?

A. 9 KW B. 26.9 KW C. 90 KW D. 15.5 KW

9.   The duration of one cycle of AC power can be divided into degrees. How many degrees are in one-half cycle of AC power?

A. 270° B. 90° C. 180° D. 360°

10.   What is the typical frequency of AC power in North America?

A. 60 Hz B. 400 Hz C. 120 Hz D. 50 Hz

11.   There are many different values associated with an AC sine wave. Which one of the following continually changes throughout the cycle?

A. peak value B. average value C. effective value D. instantaneous value

12.   When you're using the right-hand, or generator, rule your middle finger indicates the direction of what?

A. Conventional current flow B. Magnetic field C. Electron current flow D. Coil movement

Use the figure to answer the following question.

13.   The four-wire, three-phase, 220 V, delta system shown in the figure includes a center tap of winding1. A single-phase 120 V load may be safely connected between which two wires?

A. C and N B. B and C C. A and N D. A and B

14.   At what voltage level is AC power normally created by the utility?

A. 2500 VAC B. 1300 VAC C. 500 VAC D. 1000 VAC

15.   If a sine wave representing AC voltage has an effective value of 70 VAC, what would be the wave's peak value?

A. 54.96 V B. 98.98 V C. 63.81 V D. 70.49 V

16.   What is the average value of an AC voltage that has a maximum peak voltage of 80 VAC?

A. 50.88 VAC B. 38.31 VAC C. 160 VAC D. 56.56 VAC

17.   The peak value of a sine wave is 80 VAC. What is the peak-to-peak value of this waveform?

A. 60 V B. 40 V C. 160 V D. 120 V

18.   Another name for the Y- or wye-connected system of polyphase power is the

A. star system. B. delta system. C. split-phase system. D. balanced system

19.   Which one of the following values exactly matches the rms value of an AC signal?

A. Average B. Peak-to-peak C. Effective D. Peak

20.   The peak value of a sine wave is equal to 240 VAC. What is the average value of the waveform?

A. 169.68 V B. 144.14 V C. 120.74 V D. 152.64 V

21.   A technician uses an oscilloscope to measure the peak value of an AC wave. He tells you that the voltage has a peak value of 100 V. What is the rms value of the voltage?

A. 100 V B. 70.7 V C. 10 V D. 707 V

22.   If an AC current begins rising positive at 0 degrees, when will it reach its negative maximum current?

A. 360º B. 180º C. 90º D. 270º

23.   Which one of the following statements is true concerning an AC circuit that contains both resistance and inductance?

A. The current will lag the voltage. B. The current will lead the voltage. C. The voltage will lag the current. D. The current and voltage will be in phase

24.   In a certain balanced three-phase system, each line current is 5 A and each line voltage is 220 V. What is the approximate real power, if the power factor is 0.7?

A. 1334 W B. 154 W C. 1770 W D. 1100 W

25.   An AC sine wave has an effective value of 100 V. What is the peak value of the waveform?

A. 96.3 V B. 141.4 V C. 200 V D. 183 V