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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 size of a transformer is measured in...
75 turns.
The current will read zero.
Kilovolt ampere (KVA).
100 turns.

2. The standard frequency of alternating current used at a mine is...
100 turns.
60 Hertz
A device used to store electrical energy.
Continuous.

3. 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.
They must be installed at least 7 feet above the ground.
Potential transformer.
Carotid pulse - which is located in the neck next to the Adam's apple.
5:1.

4. A solenoid coil is...
An electromagnet.
Derive a neutral for grounding purposes.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Second-degree burn.

5. Current that changes periodically in direction is...
Alternating current.
100 volts.
Grounded phase and ground fault devices were not operating.
A.C.

6. The primary function of a power transformer is to provide...
Hyperventilation.
75 turns.
Electro-magnetism for their operation.
Full-load - three-phase voltage.

7. A wound-rotor induction motor has all the following EXCEPT...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
A device used to store electrical energy.
Two speeds
Squirrel-cage rotor.

8. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
75 turns.
Two speeds
277 volts.
Shunted and taped

9. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The current will read zero.
Clamp-on ammeter.
Current changing constantly in magnitude and periodically in direction.
Inductance.

10. Operating coils - motors - transformers - relays and solenoids depend upon...
7 -630 volts.
Shunted and taped
Electro-magnetism for their operation.
Derive a neutral for grounding purposes.

11. Three-phase AC underground cables must be provided with overcurrent protection using a...
800 volts.
Circuit Breaker.
Draw less current.
Lower current and higher voltage.

12. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
A.C.
150 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.
The motor rotation is reversed.

13. 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?
At the source transformer.
Capacitance.
150 turns.
5:1.

14. All transformers step voltage up or down by...
Transformer
Hyperventilation.
75 turns.
Inductance.

15. Compared to the secondary of a loaded - step-down transformer - the primary has...
Carotid pulse - which is located in the neck next to the Adam's apple.
The chest should rise or inflate.
Lower current and higher voltage
Current changing constantly in magnitude and periodically in direction.

16. Not an acceptable method for the installations of surface transformers?
Check to make sure that the victim is not still in contact with the electricity.
They must be installed at least 7 feet above the ground.
3 -979 Volts.
At least two phases

17. The secondary windings on a 10:1 step-down transformer will have a wire size...
Check to make sure that the victim is not still in contact with the electricity.
Larger than that found in the primary winding.
Isolation transformer.
They must be installed at least 7 feet above the ground.

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?
No.6 AWG.
100 turns.
The capacitors should be discharged.
Zero amps.

19. The transformer used only to measure voltage is a...
The motor rotation is reversed.
Clamp-on ammeter.
Potential transformer.
Transformer

20. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
At least two phases
1 amp.
A step-up transformer.
X.

21. The property of an electric circuit that opposes any change in current is called...
At the source transformer.
Hyperventilation.
Grounded phase and ground fault devices were not operating.
Inductance.

22. 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?
It provides good speed control.
The capacitors should be discharged.
Disconnect the frame-grounding conductor.
800 volts.

23. A transformer with a 1:1 ratio is usually a (an)...
Potential transformer.
Isolation transformer.
A step-up transformer.
Cut around clothing that has adhered to the burned area.

24. 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?
Transformer
Draw less current.
Current that changes constantly in magnitude and periodically in direction.
600 volts.

25. The standard frequency of power supplied by the power company is...
7 -630 volts.
Transformer
60 cycles per second (60 Hertz).
Electro-magnetism for their operation.

26. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
1 amp.
5:1
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
100 volts.

27. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Transformers.
1 amp.
5:1.
The capacitors should be discharged.

28. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
An electrical shock hazard may exist.
Disconnect the frame-grounding conductor.
Reverse its rotation.
3 -979 Volts.

29. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Provides single-phase power to smaller loads such as lights - heaters - etc.
800 volts.
7 -630 volts.
200 volts AC.

30. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Hyperventilation.
12 to 15 times a minute.
Check to make sure that the victim is not still in contact with the electricity.

31. Not true about AC power?
Nearly constant.
H terminals.
It provides good speed control.
Reverse any two-phase leads.

32. Not a symptom of electrical shock?.
Derive a neutral for grounding purposes.
The chest should rise or inflate.
Hyperventilation.
Nearly constant.

33. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Shunted and taped
Zero amps.
Kilovolt ampere (KVA).
60 Hertz

34. The combined capacitance of two capacitors in parallel is...
15 feet off the ground.
Tied together
Transformer
The sum of the two capacitors.

35. At what rate should mouth-to-mouth resuscitation be applied?
They should be made by the same manufacturer.
25 feet.
Kilovolt ampere (KVA).
12 to 15 times a minute.

36. 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
Clamp-on ammeter.
200 volts AC.
Hyperventilation.

37. Current in an AC circuit may be measured by...
Larger than that found in the primary winding.
3 -979 Volts.
Short-circuited after power has been removed.
Clamp-on ammeter.

38. What is the first step to be followed in aiding a victim of electrical shock?
5:1.
Check to make sure that the victim is not still in contact with the electricity.
Potential transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.

39. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
1 amp.
A step-up transformer.
At the source transformer.

40. Which of the following does a squirrel cage induction motor have?
800 volts.
They should be made by the same manufacturer.
Current changing constantly in magnitude and periodically in direction.
Stator windings.

41. 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?
Derive a neutral for grounding purposes.
Two speeds
Reverse its rotation.
75 turns.

42. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Carotid pulse - which is located in the neck next to the Adam's apple.
Potential transformer.
It provides good speed control.
The chest should rise or inflate.

43. High voltage is used to transmit power over long distances...
Current that changes constantly in magnitude and periodically in direction.
Because less current flowing at high voltage causes less line loss per kilowatt.
At least two phases
Draw less current.

44. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Larger than that found in the primary winding.
25 feet.
No.6 AWG.
The chest should rise or inflate.

45. Define alternating current...
75 turns.
Current changing constantly in magnitude and periodically in direction.
Carotid pulse - which is located in the neck next to the Adam's apple.
Transformers.

46. How should clothing be removed from a burn?
Short-circuited after power has been removed.
Cut around clothing that has adhered to the burned area.
The sum of the two capacitors.
Grounded phase and ground fault devices were not operating.

47. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
25 feet.
Current changing constantly in magnitude and periodically in direction.
800 volts.
A step-up transformer.

48. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
277 volts.
Lower current and higher voltage
A grounding resistor.
Two speeds

49. What is the danger when working around capacitors?
Lower current and higher voltage
Shunted and taped
An electrical shock hazard may exist.
Stator windings.

50. What should the duty rating of a grounding resistor be?
Hyperventilation.
Disconnect the frame-grounding conductor.
Continuous.
They should be made by the same manufacturer.