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AC Theory

Instructions:

Answer 50 questions in 30 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. Find the turns ratio of a single-phase transformer with the following values: Primary power of 5KW - secondary current of 100 amps - and primary voltage of 250 volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
5:1
At least two phases
Lower current and higher voltage.

2. Two 10-hp induction motors are operating on 460 volts AC. One motor is connected by single- phase; the other is connected in three-phase. The three-phase will...
Draw less current.
The sum of the two capacitors.
Two speeds
Nearly constant.

3. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
A grounding resistor.
15 feet off the ground.
Shunted and taped

4. The standard frequency of alternating current used at a mine is...
Lower current and higher voltage
60 Hertz
A device used to store electrical energy.
100 turns.

5. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
5:1
Kilovolt ampere (KVA).
Allow for metering voltage and Current.

6. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Larger than that found in the primary winding.
The chest should rise or inflate.
Shunted and taped
Grounded phase and ground fault devices were not operating.

7. 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?
Tied together
800 volts.
75 turns.
200 volts AC.

8. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
An electrical shock hazard may exist.
X.
100 turns.
75 turns.

9. Not true about AC power?
Lower current and higher voltage
Full-load - three-phase voltage.
It provides good speed control.
600 volts.

10. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
The chest should rise or inflate.
An electromagnet.
Clamp-on ammeter.
Grounded phase and ground fault devices were not operating.

11. AC voltage is raised or lowered by means of...
Transformers.
Potential transformer.
Reverse any two-phase leads.
7 -630 volts.

12. 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...
A grounding resistor.
Second-degree burn.
100 volts.
Squirrel-cage induction motor.

13. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
100 turns.
Current changing constantly in magnitude and periodically in direction.
Continuous.

14. What is the danger when working around capacitors?
Lower current and higher voltage
An electrical shock hazard may exist.
Two speeds
The current will read zero.

15. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
60 Hertz
Clamp-on ammeter.
H terminals.

16. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Squirrel-cage induction motor.
60 cycles per second (60 Hertz).
No.6 AWG.
75 turns.

17. The property of an electric circuit that opposes any change in current is called...
Inductance.
2000 watts
Electro-magnetism for their operation.
Continuous.

18. A transformer with a 1:1 ratio is usually a (an)...
150 turns.
Isolation transformer.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Derive a neutral for grounding purposes.

19. If any two-phase wires are reversed on a three-phase motor - the motor will...
No.6 AWG.
A grounding resistor.
Reverse its rotation.
Circuit Breaker.

20. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
277 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
480 volts.

21. 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?
A step-up transformer.
150 turns.
75 turns.
12 to 15 times a minute.

22. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Lower current and higher voltage.
Potential transformer.
H terminals.

23. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
15 feet off the ground.
Stator windings.
Electro-magnetism for their operation.
A step-up transformer.

24. What should the duty rating of a grounding resistor be?
At the source transformer.
7 -630 volts.
A device used to store electrical energy.
Continuous.

25. Not an acceptable method for the installations of surface transformers?
X.
They must be installed at least 7 feet above the ground.
Current that changes constantly in magnitude and periodically in direction.
Current changing constantly in magnitude and periodically in direction.

26. 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...
At least two phases
Full-load - three-phase voltage.
Draw less current.
Stator windings.

27. The most reliable method to use to determine whether or not the heart has stopped is by checking the...

28. Define alternating current...
An electromagnet.
The sum of the two capacitors.
Current changing constantly in magnitude and periodically in direction.
12 to 15 times a minute.

29. The size of a transformer is measured in...
60 cycles per second (60 Hertz).
The sum of the two capacitors.
Kilovolt ampere (KVA).
Electro-magnetism for their operation.

30. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Grounded phase and ground fault devices were not operating.
Alternating current.
The motor rotation is reversed.
The current will read zero.

31. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
Check to make sure that the victim is not still in contact with the electricity.
Zero amps.
25 feet.

32. What is the first step to be followed in aiding a victim of electrical shock?
5:1
Derive a neutral for grounding purposes.
Check to make sure that the victim is not still in contact with the electricity.
60 Hertz

33. 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?
Clamp-on ammeter.
600 volts.
800 volts.
277 volts.

34. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Kilovolt ampere (KVA).
At the source transformer.
At least two phases
800 volts.

35. What type motor is a wound-rotor induction motor?
The sum of the two capacitors.
Check to make sure that the victim is not still in contact with the electricity.
3 -979 Volts.
A.C.

36. Compared to the secondary of a loaded - step-down transformer - the primary has...
Hyperventilation.
Lower current and higher voltage.
Larger than that found in the primary winding.
Draw less current.

37. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
A grounding resistor.
Kilovolt ampere (KVA).

38. Current in an AC circuit may be measured by...
Allow for metering voltage and Current.
Clamp-on ammeter.
60 cycles per second (60 Hertz).
Hyperventilation.

39. Current that changes periodically in direction is...
Carotid pulse - which is located in the neck next to the Adam's apple.
Alternating current.
A.C.
100 volts.

40. The speed of an alternating current - squirrel-cage induction motor is...
The capacitors should be discharged.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Nearly constant.
Provides single-phase power to smaller loads such as lights - heaters - etc.

41. Three-phase AC underground cables must be provided with overcurrent protection using a...
Because less current flowing at high voltage causes less line loss per kilowatt.
Four times less than that of the secondary.
Circuit Breaker.
480 volts.

42. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
7 -630 volts.
Current that changes constantly in magnitude and periodically in direction.
480 volts.
Kilovolt ampere (KVA).

43. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Larger than that found in the primary winding.
Disconnect the frame-grounding conductor.
Capacitance.
Reverse its rotation.

44. All transformers step voltage up or down by...
Reverse any two-phase leads.
Inductance.
7 -630 volts.
Isolation transformer.

45. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Draw less current.
7 -630 volts.
An electromagnet.
Zero amps.

46. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
They must be installed at least 7 feet above the ground.
Squirrel-cage induction motor.
Grounded phase and ground fault devices were not operating.
Four times less than that of the secondary.

47. Alternating current may be defined as...
Cut around clothing that has adhered to the burned area.
Current that changes constantly in magnitude and periodically in direction.
1 amp.
60 Hertz

48. At what rate should mouth-to-mouth resuscitation be applied?
Squirrel-cage induction motor.
12 to 15 times a minute.
Continuous.
It provides good speed control.

49. The primary leads of a single-phase transformer should be connected to the...
A.C.
X.
The motor rotation is reversed.
H terminals.

50. Where should grounding resistors be located?
Disconnect the frame-grounding conductor.
7 -630 volts.
Continuous.
At the source transformer.