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AC Theory

Instructions:

Answer 50 questions in 15 minutes.
If you are not ready to take this test, you can study here.
Match each statement with the correct term.
Don't refresh. All questions and answers are randomly picked and ordered every time you load a test.

This is a study tool. The 3 wrong answers for each question are randomly chosen from answers to other questions. So, you might find at times the answers obvious, but you will see it re-enforces your understanding as you take the test each time.

1. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
The chest should rise or inflate.
15 feet off the ground.
Squirrel-cage rotor.

2. What is a capacitor?
A device used to store electrical energy.
7 -630 volts.
The current will read zero.
800 volts.

3. A transformer has 2000 turns in the primary and 500 turns in the secondary. The primary voltage is 3 -200 volts. What is the secondary voltage?
Hyperventilation.
It provides good speed control.
Provides single-phase power to smaller loads such as lights - heaters - etc.
800 volts.

4. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Circuit Breaker.
The motor rotation is reversed.
Draw less current.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

5. The standard frequency of power supplied by the power company is...
H terminals.
60 cycles per second (60 Hertz).
7 -630 volts.
Electro-magnetism for their operation.

6. A transformer with a 1:1 ratio is usually a (an)...
12 to 15 times a minute.
Isolation transformer.
Second-degree burn.
X.

7. The transformer used only to measure voltage is a...
200 volts AC.
Larger than that found in the primary winding.
The motor rotation is reversed.
Potential transformer.

8. At what rate should mouth-to-mouth resuscitation be applied?
600 volts.
Nearly constant.
12 to 15 times a minute.
200 volts AC.

9. Find the turns ratio of a single-phase transformer with the following values: Primary power of 10 KW - secondary current of 200 amps - and primary voltage of 250 volts.
The capacitors should be discharged.
Draw less current.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
5:1.

10. The size of a transformer is measured in...
480 volts.
Four times less than that of the secondary.
Kilovolt ampere (KVA).
Circuit Breaker.

11. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
The sum of the two capacitors.
Allow for metering voltage and Current.
The chest should rise or inflate.

12. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
800 volts.
277 volts.
No.6 AWG.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

13. 460 volts AC is required to operate two motors - one connected in single-phase and the other connected in three-phase. The three-phase motor will...
Lower current and higher voltage.
Reverse its rotation.
Draw less current.
5:1.

14. Current in an AC circuit may be measured by...
Potential transformer.
The capacitors should be discharged.
Full-load - three-phase voltage.
Clamp-on ammeter.

15. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
H terminals.
1 amp.
Grounded phase and ground fault devices were not operating.
Disconnect the frame-grounding conductor.

16. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Inductance.
Alternating current.
Electro-magnetism for their operation.
No.6 AWG.

17. How should clothing be removed from a burn?
Check to make sure that the victim is not still in contact with the electricity.
Cut around clothing that has adhered to the burned area.
Potential transformer.
An electromagnet.

18. A transformer has a primary voltage of 2 -400 volts and a secondary reading of 120 volts. If there are 1 -500 turns on the primary - how many turns are on the secondary?
A grounding resistor.
Electro-magnetism for their operation.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
75 turns.

19. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
No.6 AWG.
They should be made by the same manufacturer.
Capacitance.
The current will read zero.

20. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
Carotid pulse - which is located in the neck next to the Adam's apple.
Inductance.
Squirrel-cage induction motor.

21. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Grounded phase and ground fault devices were not operating.
Clamp-on ammeter.
Full-load - three-phase voltage.
A grounding resistor.

22. Under fault conditions - the grounding resistor in a high voltage circuit limits the voltage drop in the grounding circuit external to the resistor to not more than...
Allow for metering voltage and Current.
100 volts.
480 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

23. Define alternating current...
Grounded phase and ground fault devices were not operating.
Current changing constantly in magnitude and periodically in direction.
600 volts.
Capacitance.

24. The combined capacitance of two capacitors in parallel is...
The capacitors should be discharged.
Disconnect the frame-grounding conductor.
Capacitance.
The sum of the two capacitors.

25. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Transformer
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Hyperventilation.

26. What steps up or steps down AC voltage?
Lower current and higher voltage.
Transformer
Capacitance.
Isolation transformer.

27. The speed of an alternating current - squirrel-cage induction motor is...
An electrical shock hazard may exist.
Continuous.
Nearly constant.
Draw less current.

28. AC voltage is raised or lowered by means of...
Full-load - three-phase voltage.
Lower current and higher voltage
Transformers.
Cut around clothing that has adhered to the burned area.

29. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Capacitance.
A step-up transformer.
Grounded phase and ground fault devices were not operating.
Circuit Breaker.

30. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Current that changes constantly in magnitude and periodically in direction.
At least two phases
Check to make sure that the victim is not still in contact with the electricity.
800 volts.

31. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
They must be installed at least 7 feet above the ground.
It provides good speed control.
Check to make sure that the victim is not still in contact with the electricity.

32. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
Inductance.
Second-degree burn.
7 -630 volts.

33. Alternating current may be defined as...
Squirrel-cage induction motor.
Current that changes constantly in magnitude and periodically in direction.
Allow for metering voltage and Current.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

34. The primary leads of a single-phase transformer should be connected to the...
277 volts.
Draw less current.
H terminals.
Full-load - three-phase voltage.

35. The main function of CT's and PT's on a main substation is to...
100 turns.
Allow for metering voltage and Current.
Clamp-on ammeter.
Inductance.

36. When not connected to a load - the secondary leads of a current transformer should be...
5:1.
277 volts.
Allow for metering voltage and Current.
Shunted and taped

37. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
200 volts AC.
A.C.
800 volts.
Short-circuited after power has been removed.

38. A transformer with 3000 turns in the primary winding has a primary voltage of 4 -800 volts and a secondary voltage of 240 volts. How many turns are in the secondary winding?
Inductance.
A.C.
150 turns.
Potential transformer.

39. What position of a selector switch using a voltmeter would you select to check a 120-volt AC circuit to obtain the most accurate reading?
Reverse its rotation.
Current changing constantly in magnitude and periodically in direction.
200 volts AC.
The capacitors should be discharged.

40. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
They should be made by the same manufacturer.
Second-degree burn.
The sum of the two capacitors.
Clamp-on ammeter.

41. Three-phase AC underground cables must be provided with overcurrent protection using a...
480 volts.
Circuit Breaker.
A step-up transformer.
Lower current and higher voltage

42. Current that changes periodically in direction is...
Alternating current.
Continuous.
5:1.
15 feet off the ground.

43. A solenoid coil is...
An electromagnet.
1 amp.
Transformer
Reverse its rotation.

44. What is the danger when working around capacitors?
60 Hertz
An electrical shock hazard may exist.
At the source transformer.
1 amp.

45. Not true about AC power?
It provides good speed control.
Current changing constantly in magnitude and periodically in direction.
A grounding resistor.
Four times less than that of the secondary.

46. What type motor is a wound-rotor induction motor?
A.C.
At least two phases
Two speeds
A grounding resistor.

47. What value of voltage will be measured from phase-to-phase - in a wye-connected secondary - if 2 -300 volts is measured from phase-to-ground?
The motor rotation is reversed.
Isolation transformer.
3 -979 Volts.
Current that changes constantly in magnitude and periodically in direction.

48. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
1 amp.
7 -630 volts.
Capacitance.
Two speeds

49. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
7 -630 volts.
Larger than that found in the primary winding.
Inductance.
60 Hertz

50. The primary function of a power transformer is to provide...
Clamp-on ammeter.
Four times less than that of the secondary.
Full-load - three-phase voltage.
5:1