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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. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
25 feet.
Electro-magnetism for their operation.
A device used to store electrical energy.

2. A transformer has 1 -600 turns in the primary and 400 turns in the secondary. The primary voltage is 2 -400 volts. What is the secondary voltage?
75 turns.
60 cycles per second (60 Hertz).
A grounding resistor.
600 volts.

3. Not true about AC power?
Carotid pulse - which is located in the neck next to the Adam's apple.
An electromagnet.
Grounded phase and ground fault devices were not operating.
It provides good speed control.

4. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
Transformers.
Carotid pulse - which is located in the neck next to the Adam's apple.
Full-load - three-phase voltage.

5. What is a capacitor?
A device used to store electrical energy.
Disconnect the frame-grounding conductor.
100 volts.
They must be installed at least 7 feet above the ground.

6. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Hyperventilation.
60 cycles per second (60 Hertz).
A grounding resistor.
Squirrel-cage rotor.

7. At what rate should mouth-to-mouth resuscitation be applied?
75 turns.
12 to 15 times a minute.
Electro-magnetism for their operation.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

8. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
A grounding resistor.
Capacitance.
The capacitors should be discharged.

9. What is the danger when working around capacitors?
15 feet off the ground.
Current that changes constantly in magnitude and periodically in direction.
An electrical shock hazard may exist.
Allow for metering voltage and Current.

10. The purpose of a zig-zag transformer is to...
Squirrel-cage rotor.
A step-up transformer.
Derive a neutral for grounding purposes.
600 volts.

11. 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...
Alternating current.
Stator windings.
Tied together
Draw less current.

12. The primary function of a power transformer is to provide...
60 Hertz
X.
Full-load - three-phase voltage.
Inductance.

13. A transformer with 1 -500 turns in the primary winding has a primary voltage of 2 -400 volts and a secondary voltage of 120 volts. How many turns are in the secondary winding?
75 turns.
800 volts.
An electromagnet.
Kilovolt ampere (KVA).

14. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
75 turns.
7 -630 volts.
480 volts.
277 volts.

15. Compared to the secondary of a loaded - step-down transformer - the primary has...
150 turns.
Lower current and higher voltage
Full-load - three-phase voltage.
Isolation transformer.

16. A burn causing a blister is classified as a...
Second-degree burn.
A device used to store electrical energy.
5:1
Clamp-on ammeter.

17. What should the duty rating of a grounding resistor be?
Stator windings.
A grounding resistor.
Continuous.
Transformers.

18. The transformer used only to measure voltage is a...
Zero amps.
Potential transformer.
Current that changes constantly in magnitude and periodically in direction.
Transformer

19. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
Squirrel-cage induction motor.
Draw less current.
Reverse any two-phase leads.

20. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
800 volts.
15 feet off the ground.
Potential transformer.
Electro-magnetism for their operation.

21. Three-phase AC underground cables must be provided with overcurrent protection using a...
A step-up transformer.
Grounded phase and ground fault devices were not operating.
Shunted and taped
Circuit Breaker.

22. A control power transformer...
Full-load - three-phase voltage.
They should be made by the same manufacturer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Squirrel-cage induction motor.

23. Alternating current may be defined as...
It provides good speed control.
Current that changes constantly in magnitude and periodically in direction.
Allow for metering voltage and Current.
Two speeds

24. A 3-phase - 2 speed - constant torque motor is running at fast speed. The motor windings are connected wye for fast speed. Motor leads T4 - T5 and T6 are connected to the line leads. Motor leads T1 - T2 and T3 should be...
The current will read zero.
X.
Squirrel-cage induction motor.
Tied together

25. 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?
75 turns.
Reverse its rotation.
Draw less current.
3 -979 Volts.

26. AC voltage is raised or lowered by means of...
The current will read zero.
Transformers.
They should be made by the same manufacturer.
200 volts AC.

27. 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?
The motor rotation is reversed.
They must be installed at least 7 feet above the ground.
800 volts.
They should be made by the same manufacturer.

28. The secondary windings on a 10:1 step-down transformer will have a wire size...
Inductance.
Disconnect the frame-grounding conductor.
X.
Larger than that found in the primary winding.

29. 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?
The capacitors should be discharged.
800 volts.
Transformer
150 turns.

30. 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?
200 volts AC.
Circuit Breaker.
100 turns.
Alternating current.

31. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Zero amps.
Disconnect the frame-grounding conductor.
25 feet.
Lower current and higher voltage.

32. What type motor is a wound-rotor induction motor?
A.C.
Current changing constantly in magnitude and periodically in direction.
Nearly constant.
Draw less current.

33. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Circuit Breaker.
Two speeds
Squirrel-cage induction motor.
Second-degree burn.

34. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The motor rotation is reversed.
480 volts.
100 turns.
Grounded phase and ground fault devices were not operating.

35. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Provides single-phase power to smaller loads such as lights - heaters - etc.
Zero amps.
Inductance.
2000 watts

36. The standard frequency of alternating current used at a mine is...
Squirrel-cage rotor.
60 Hertz
Second-degree burn.
Squirrel-cage induction motor.

37. Not a symptom of electrical shock?.
The capacitors should be discharged.
7 -630 volts.
Check to make sure that the victim is not still in contact with the electricity.
Hyperventilation.

38. Compared to the secondary of a loaded - step-down transformer - the primary has...
Alternating current.
Full-load - three-phase voltage.
Lower current and higher voltage.
A grounding resistor.

39. All transformers step voltage up or down by...
Inductance.
Carotid pulse - which is located in the neck next to the Adam's apple.
Reverse any two-phase leads.
25 feet.

40. What steps up or steps down AC voltage?
Transformer
Circuit Breaker.
They must be installed at least 7 feet above the ground.
X.

41. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
100 volts.
Cut around clothing that has adhered to the burned area.
The motor rotation is reversed.

42. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Nearly constant.
A grounding resistor.
X.

43. The size of a transformer is measured in...
60 Hertz
Kilovolt ampere (KVA).
Alternating current.
A grounding resistor.

44. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Reverse its rotation.
No.6 AWG.
The motor rotation is reversed.
At least two phases

45. The standard frequency of power supplied by the power company is...
5:1.
It provides good speed control.
H terminals.
60 cycles per second (60 Hertz).

46. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
The sum of the two capacitors.
75 turns.
No.6 AWG.

47. The property of an electric circuit that opposes any change in current is called...
Inductance.
2000 watts
Tied together
A step-up transformer.

48. 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.
Zero amps.
Grounded phase and ground fault devices were not operating.
Current changing constantly in magnitude and periodically in direction.
5:1.

49. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Shunted and taped
25 feet.
Draw less current.

50. Which of the following does a squirrel cage induction motor have?
Provides single-phase power to smaller loads such as lights - heaters - etc.
Zero amps.
Stator windings.
3 -979 Volts.