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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. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
2000 watts
277 volts.
1 amp.
480 volts.

2. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Disconnect the frame-grounding conductor.
An electromagnet.
7 -630 volts.
Grounded phase and ground fault devices were not operating.

3. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
An electromagnet.
Continuous.
The chest should rise or inflate.
Electro-magnetism for their operation.

4. A transformer with a 1:1 ratio is usually a (an)...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Stator windings.
2000 watts
Isolation transformer.

5. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
150 turns.
Two speeds
Draw less current.

6. A wound-rotor induction motor has all the following EXCEPT...
Allow for metering voltage and Current.
5:1
25 feet.
Squirrel-cage rotor.

7. The main function of CT's and PT's on a main substation is to...
Because less current flowing at high voltage causes less line loss per kilowatt.
Hyperventilation.
Allow for metering voltage and Current.
Four times less than that of the secondary.

8. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
75 turns.
Cut around clothing that has adhered to the burned area.
Short-circuited after power has been removed.
Squirrel-cage rotor.

9. What should the duty rating of a grounding resistor be?
1 amp.
Continuous.
Current that changes constantly in magnitude and periodically in direction.
At the source transformer.

10. What is a capacitor?
H terminals.
Draw less current.
A device used to store electrical energy.
Stator windings.

11. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The motor rotation is reversed.
Kilovolt ampere (KVA).
Carotid pulse - which is located in the neck next to the Adam's apple.

12. To protect against over-current in a three-phase circuit over-current protection must be provided for...
The motor rotation is reversed.
The chest should rise or inflate.
Tied together
At least two phases

13. 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...
75 turns.
Stator windings.
100 volts.
Hyperventilation.

14. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Second-degree burn.
The current will read zero.
An electrical shock hazard may exist.
H terminals.

15. The primary leads of a single-phase transformer should be connected to the...
Second-degree burn.
H terminals.
Allow for metering voltage and Current.
5:1.

16. The primary function of a power transformer is to provide...
An electromagnet.
Full-load - three-phase voltage.
The current will read zero.
A grounding resistor.

17. When not connected to a load - the secondary leads of a current transformer should be...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Shunted and taped
12 to 15 times a minute.
Capacitance.

18. Current that changes periodically in direction is...
Shunted and taped
Continuous.
1 amp.
Alternating current.

19. The standard frequency of power supplied by the power company is...
Two speeds
60 cycles per second (60 Hertz).
The sum of the two capacitors.
100 turns.

20. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
They must be installed at least 7 feet above the ground.
Transformer
Stator windings.

21. The purpose of a zig-zag transformer is to...
Transformers.
25 feet.
Derive a neutral for grounding purposes.
Reverse its rotation.

22. Not a symptom of electrical shock?.
Derive a neutral for grounding purposes.
Kilovolt ampere (KVA).
A grounding resistor.
Hyperventilation.

23. How should clothing be removed from a burn?
Short-circuited after power has been removed.
100 turns.
Cut around clothing that has adhered to the burned area.
A.C.

24. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
Stator windings.
Continuous.
Two speeds

25. Compared to the secondary of a loaded - step-down transformer - the primary has...
X.
Draw less current.
60 Hertz
Lower current and higher voltage.

26. What type of 3-phase AC motor is used most often around a mine?
75 turns.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
100 volts.
Squirrel-cage induction motor.

27. Which of the following does a squirrel cage induction motor have?
Stator windings.
60 Hertz
100 turns.
Zero amps.

28. A burn causing a blister is classified as a...
Second-degree burn.
It provides good speed control.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Continuous.

29. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Stator windings.
15 feet off the ground.

30. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
100 turns.
They should be made by the same manufacturer.
The current will read zero.
Because less current flowing at high voltage causes less line loss per kilowatt.

31. The property of an electrical circuit that opposes any change in voltage is called...
Potential transformer.
The sum of the two capacitors.
The capacitors should be discharged.
Capacitance.

32. The standard frequency of alternating current used at a mine is...
Kilovolt ampere (KVA).
60 Hertz
At the source transformer.
7 -630 volts.

33. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
277 volts.
12 to 15 times a minute.
Potential transformer.
480 volts.

34. The property of an electric circuit that opposes any change in current is called...
Inductance.
Shunted and taped
No.6 AWG.
Lower current and higher voltage.

35. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
1 amp.
A grounding resistor.
60 cycles per second (60 Hertz).

36. 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?
Because less current flowing at high voltage causes less line loss per kilowatt.
Reverse any two-phase leads.
Lower current and higher voltage
75 turns.

37. 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...
Lower current and higher voltage
Short-circuited after power has been removed.
Draw less current.
3 -979 Volts.

38. Define alternating current...
An electrical shock hazard may exist.
600 volts.
Reverse any two-phase leads.
Current changing constantly in magnitude and periodically in direction.

39. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
An electrical shock hazard may exist.
Grounded phase and ground fault devices were not operating.
480 volts.

40. The size of a transformer is measured in...
Kilovolt ampere (KVA).
No.6 AWG.
480 volts.
At the source transformer.

41. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
A step-up transformer.
A grounding resistor.
7 -630 volts.
Continuous.

42. 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...
75 turns.
Clamp-on ammeter.
Tied together
60 Hertz

43. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
2000 watts
A.C.
15 feet off the ground.
277 volts.

44. 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?
150 turns.
Full-load - three-phase voltage.
A step-up transformer.
It provides good speed control.

45. The secondary windings on a 10:1 step-down transformer will have a wire size...
Stator windings.
Larger than that found in the primary winding.
Tied together
Capacitance.

46. 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?
X.
Tied together
Alternating current.
200 volts AC.

47. 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.
At the source transformer.
Squirrel-cage rotor.
Transformers.

48. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
5:1
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Allow for metering voltage and Current.
The chest should rise or inflate.

49. Not true about AC power?
15 feet off the ground.
Lower current and higher voltage.
It provides good speed control.
200 volts AC.

50. 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?
Current changing constantly in magnitude and periodically in direction.
800 volts.
The chest should rise or inflate.
Circuit Breaker.