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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. The property of an electric circuit that opposes any change in current is called...
1 amp.
Inductance.
Second-degree burn.
Carotid pulse - which is located in the neck next to the Adam's apple.

2. 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...
150 turns.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Hyperventilation.
100 volts.

3. Which of the following does a squirrel cage induction motor have?
Transformer
Short-circuited after power has been removed.
Stator windings.
1 amp.

4. The standard frequency of alternating current used at a mine is...
1 amp.
60 cycles per second (60 Hertz).
Two speeds
60 Hertz

5. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
75 turns.
Transformers.
7 -630 volts.
800 volts.

6. Compared to the secondary of a loaded - step-down transformer - the primary has...
Cut around clothing that has adhered to the burned area.
A device used to store electrical energy.
Disconnect the frame-grounding conductor.
Lower current and higher voltage

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?
An electromagnet.
200 volts AC.
Circuit Breaker.
Larger than that found in the primary winding.

8. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Alternating current.
The chest should rise or inflate.
1 amp.
Hyperventilation.

9. 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?
3 -979 Volts.
The chest should rise or inflate.
Circuit Breaker.
A device used to store electrical energy.

10. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Electro-magnetism for their operation.
A.C.
Because less current flowing at high voltage causes less line loss per kilowatt.

11. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
An electrical shock hazard may exist.
A.C.
800 volts.
A step-up transformer.

12. 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.
No.6 AWG.
Kilovolt ampere (KVA).
100 volts.

13. Not a symptom of electrical shock?.
800 volts.
Derive a neutral for grounding purposes.
Potential transformer.
Hyperventilation.

14. High voltage is used to transmit power over long distances...
Inductance.
Because less current flowing at high voltage causes less line loss per kilowatt.
12 to 15 times a minute.
3 -979 Volts.

15. The size of a transformer is measured in...
Kilovolt ampere (KVA).
75 turns.
Transformers.
Inductance.

16. The standard frequency of power supplied by the power company is...
Draw less current.
The capacitors should be discharged.
Clamp-on ammeter.
60 cycles per second (60 Hertz).

17. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
No.6 AWG.
The motor rotation is reversed.
A device used to store electrical energy.

18. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
25 feet.
Derive a neutral for grounding purposes.
Two speeds

19. 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?
Kilovolt ampere (KVA).
75 turns.
Current that changes constantly in magnitude and periodically in direction.
H terminals.

20. Define alternating current...
Disconnect the frame-grounding conductor.
Full-load - three-phase voltage.
Current changing constantly in magnitude and periodically in direction.
X.

21. A wound-rotor induction motor has all the following EXCEPT...
Inductance.
The motor rotation is reversed.
Squirrel-cage rotor.
Capacitance.

22. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Inductance.
Zero amps.
A grounding resistor.
They must be installed at least 7 feet above the ground.

23. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Two speeds
Capacitance.
Lower current and higher voltage
The current will read zero.

24. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
5:1
No.6 AWG.
They should be made by the same manufacturer.
Lower current and higher voltage.

25. 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.
Lower current and higher voltage
Grounded phase and ground fault devices were not operating.
5:1
A.C.

26. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
No.6 AWG.
5:1
Nearly constant.
25 feet.

27. The property of an electrical circuit that opposes any change in voltage is called...
Squirrel-cage rotor.
Current changing constantly in magnitude and periodically in direction.
Capacitance.
3 -979 Volts.

28. 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...
Tied together
Kilovolt ampere (KVA).
100 turns.
The capacitors should be discharged.

29. The speed of an alternating current - squirrel-cage induction motor is...
Transformer
5:1
Clamp-on ammeter.
Nearly constant.

30. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
The motor rotation is reversed.
Check to make sure that the victim is not still in contact with the electricity.
Reverse its rotation.

31. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Tied together
The motor rotation is reversed.
Reverse any two-phase leads.
2000 watts

32. The transformer used only to measure voltage is a...
Squirrel-cage rotor.
Cut around clothing that has adhered to the burned area.
Inductance.
Potential transformer.

33. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
100 volts.
100 turns.
1 amp.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

34. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
75 turns.
The capacitors should be discharged.
Full-load - three-phase voltage.
60 cycles per second (60 Hertz).

35. The primary function of a power transformer is to provide...
Circuit Breaker.
Full-load - three-phase voltage.
600 volts.
Squirrel-cage induction motor.

36. A solenoid coil is...
Provides single-phase power to smaller loads such as lights - heaters - etc.
15 feet off the ground.
Two speeds
An electromagnet.

37. Where should grounding resistors be located?
Allow for metering voltage and Current.
At the source transformer.
Reverse any two-phase leads.
Disconnect the frame-grounding conductor.

38. 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.
Because less current flowing at high voltage causes less line loss per kilowatt.
A.C.
No.6 AWG.

39. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Cut around clothing that has adhered to the burned area.
They should be made by the same manufacturer.
Continuous.

40. 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?
Cut around clothing that has adhered to the burned area.
600 volts.
Squirrel-cage induction motor.
3 -979 Volts.

41. Operating coils - motors - transformers - relays and solenoids depend upon...
They must be installed at least 7 feet above the ground.
Electro-magnetism for their operation.
7 -630 volts.
Short-circuited after power has been removed.

42. Current in an AC circuit may be measured by...
Shunted and taped
Clamp-on ammeter.
Transformers.
An electrical shock hazard may exist.

43. Current that changes periodically in direction is...
Alternating current.
Tied together
Reverse any two-phase leads.
Inductance.

44. AC voltage is raised or lowered by means of...
No.6 AWG.
100 turns.
Transformers.
Short-circuited after power has been removed.

45. Three-phase AC underground cables must be provided with overcurrent protection using a...
Continuous.
Inductance.
X.
Circuit Breaker.

46. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
Transformers.
Carotid pulse - which is located in the neck next to the Adam's apple.
Kilovolt ampere (KVA).

47. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
X.
1 amp.
Reverse its rotation.
At the source transformer.

48. 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?
277 volts.
800 volts.
Stator windings.
Capacitance.

49. What is the danger when working around capacitors?
12 to 15 times a minute.
2000 watts
An electrical shock hazard may exist.
Provides single-phase power to smaller loads such as lights - heaters - etc.

50. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Clamp-on ammeter.
At least two phases
200 volts AC.
Cut around clothing that has adhered to the burned area.