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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. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
7 -630 volts.
They should be made by the same manufacturer.
Second-degree burn.
600 volts.

2. AC voltage is raised or lowered by means of...
Carotid pulse - which is located in the neck next to the Adam's apple.
Transformers.
A grounding resistor.
Two speeds

3. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
A.C.
12 to 15 times a minute.
The current will read zero.
They should be made by the same manufacturer.

4. 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?
60 cycles per second (60 Hertz).
Shunted and taped
75 turns.
Transformer

5. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Squirrel-cage rotor.
X.
A step-up transformer.
15 feet off the ground.

6. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Lower current and higher voltage
At least two phases
They should be made by the same manufacturer.

7. Current transformers - or CT's - are used to...
200 volts AC.
Capacitance.
A step-up transformer.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

8. 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.
Reverse any two-phase leads.
Grounded phase and ground fault devices were not operating.

9. The primary function of a power transformer is to provide...
Clamp-on ammeter.
Tied together
The sum of the two capacitors.
Full-load - three-phase voltage.

10. The purpose of a zig-zag transformer is to...
600 volts.
Derive a neutral for grounding purposes.
Nearly constant.
150 turns.

11. 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?
75 turns.
Grounded phase and ground fault devices were not operating.
3 -979 Volts.
Draw less current.

12. The combined capacitance of two capacitors in parallel is...
800 volts.
5:1
The sum of the two capacitors.
Lower current and higher voltage

13. The standard frequency of alternating current used at a mine is...
Allow for metering voltage and Current.
Inductance.
The motor rotation is reversed.
60 Hertz

14. What should the duty rating of a grounding resistor be?
Nearly constant.
The motor rotation is reversed.
Shunted and taped
Continuous.

15. What type motor is a wound-rotor induction motor?
Derive a neutral for grounding purposes.
Hyperventilation.
A.C.
277 volts.

16. Define alternating current...
The current will read zero.
Current changing constantly in magnitude and periodically in direction.
Kilovolt ampere (KVA).
Transformer

17. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
No.6 AWG.
Lower current and higher voltage.
2000 watts
5:1

18. A transformer has a primary voltage of 2 -800 volts and a secondary reading of 140 volts. If there are 2000 turns on the primary - how many turns are on the secondary?
Lower current and higher voltage.
100 turns.
An electromagnet.
It provides good speed control.

19. What type of 3-phase AC motor is used most often around a mine?
Capacitance.
3 -979 Volts.
Squirrel-cage induction motor.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

20. When not connected to a load - the secondary leads of a current transformer should be...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Shunted and taped
Squirrel-cage induction motor.
7 -630 volts.

21. Which of the following does a squirrel cage induction motor have?
60 cycles per second (60 Hertz).
Shunted and taped
X.
Stator windings.

22. 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...
Short-circuited after power has been removed.
Kilovolt ampere (KVA).
Draw less current.
100 turns.

23. Current in an AC circuit may be measured by...
Electro-magnetism for their operation.
1 amp.
Clamp-on ammeter.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

24. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
They should be made by the same manufacturer.
60 cycles per second (60 Hertz).
The current will read zero.
1 amp.

25. How do you change the direction of a 3-phase AC motor?
Derive a neutral for grounding purposes.
An electrical shock hazard may exist.
The capacitors should be discharged.
Reverse any two-phase leads.

26. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
25 feet.
Four times less than that of the secondary.
480 volts.
3 -979 Volts.

27. The standard frequency of power supplied by the power company is...
480 volts.
Transformers.
H terminals.
60 cycles per second (60 Hertz).

28. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
1 amp.
The chest should rise or inflate.
Squirrel-cage induction motor.
An electrical shock hazard may exist.

29. Current that changes periodically in direction is...
Hyperventilation.
5:1.
Alternating current.
100 volts.

30. 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.
A grounding resistor.
5:1
75 turns.
X.

31. Operating coils - motors - transformers - relays and solenoids depend upon...
Because less current flowing at high voltage causes less line loss per kilowatt.
A step-up transformer.
200 volts AC.
Electro-magnetism for their operation.

32. 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.
5:1.
600 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
75 turns.

33. What is the danger when working around capacitors?
12 to 15 times a minute.
A device used to store electrical energy.
15 feet off the ground.
An electrical shock hazard may exist.

34. What is the first step to be followed in aiding a victim of electrical shock?
Check to make sure that the victim is not still in contact with the electricity.
Inductance.
Alternating current.
60 cycles per second (60 Hertz).

35. If any two-phase wires are reversed on a three-phase motor - the motor will...
A.C.
Draw less current.
Reverse its rotation.
Transformers.

36. To protect against over-current in a three-phase circuit over-current protection must be provided for...
The capacitors should be discharged.
No.6 AWG.
277 volts.
At least two phases

37. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
12 to 15 times a minute.
H terminals.
The current will read zero.

38. 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.
Full-load - three-phase voltage.
Reverse any two-phase leads.
X.

39. High voltage is used to transmit power over long distances...
X.
75 turns.
Reverse its rotation.
Because less current flowing at high voltage causes less line loss per kilowatt.

40. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
15 feet off the ground.
75 turns.
Draw less current.

41. 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.
H terminals.
Zero amps.
At the source transformer.

42. At what rate should mouth-to-mouth resuscitation be applied?
Capacitance.
12 to 15 times a minute.
600 volts.
Two speeds

43. A solenoid coil is...
An electromagnet.
Provides single-phase power to smaller loads such as lights - heaters - etc.
277 volts.
Short-circuited after power has been removed.

44. Compared to the secondary of a loaded - step-down transformer - the primary has...
800 volts.
Lower current and higher voltage
Alternating current.
Cut around clothing that has adhered to the burned area.

45. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Four times less than that of the secondary.
X.
Carotid pulse - which is located in the neck next to the Adam's apple.
The motor rotation is reversed.

46. Not a symptom of electrical shock?.
Lower current and higher voltage
Derive a neutral for grounding purposes.
Hyperventilation.
Electro-magnetism for their operation.

47. Where should grounding resistors be located?
At the source transformer.
Derive a neutral for grounding purposes.
Continuous.
Squirrel-cage induction motor.

48. The primary leads of a single-phase transformer should be connected to the...
No.6 AWG.
277 volts.
800 volts.
H terminals.

49. A transformer with a 1:1 ratio is usually a (an)...
Transformers.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
They must be installed at least 7 feet above the ground.
Isolation transformer.

50. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Provides single-phase power to smaller loads such as lights - heaters - etc.
No.6 AWG.
Inductance.
100 volts.