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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. Current in an AC circuit may be measured by...
X.
Clamp-on ammeter.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
150 turns.

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...
Potential transformer.
150 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.
100 volts.

3. 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.
Cut around clothing that has adhered to the burned area.
5:1
Stator windings.
Nearly constant.

4. How should clothing be removed from a burn?
Two speeds
A device used to store electrical energy.
Cut around clothing that has adhered to the burned area.
An electrical shock hazard may exist.

5. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
200 volts AC.
A device used to store electrical energy.

6. Compared to the secondary of a loaded - step-down transformer - the primary has...
5:1.
Cut around clothing that has adhered to the burned area.
Lower current and higher voltage
X.

7. Where should grounding resistors be located?
At the source transformer.
Second-degree burn.
X.
100 volts.

8. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Draw less current.
Check to make sure that the victim is not still in contact with the electricity.
Squirrel-cage rotor.

9. The primary leads of a single-phase transformer should be connected to the...
277 volts.
Lower current and higher voltage
H terminals.
Capacitance.

10. 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
277 volts.
5:1.
H terminals.

11. The property of an electric circuit that opposes any change in current is called...
Inductance.
100 volts.
Short-circuited after power has been removed.
25 feet.

12. Current that changes periodically in direction is...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
3 -979 Volts.
Alternating current.
A.C.

13. 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?
100 turns.
800 volts.
480 volts.
Cut around clothing that has adhered to the burned area.

14. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
277 volts.
Lower current and higher voltage.
Shunted and taped
Circuit Breaker.

15. What steps up or steps down AC voltage?
Draw less current.
Hyperventilation.
Transformer
Reverse its rotation.

16. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Capacitance.
Lower current and higher voltage.
A grounding resistor.

17. 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.
Grounded phase and ground fault devices were not operating.
Hyperventilation.
Electro-magnetism for their operation.

18. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Capacitance.
The current will read zero.
Nearly constant.
5:1.

19. The main function of CT's and PT's on a main substation is to...
1 amp.
2000 watts
Allow for metering voltage and Current.
Nearly constant.

20. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Potential transformer.
5:1.
Four times less than that of the secondary.
X.

21. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Zero amps.
Reverse its rotation.
The motor rotation is reversed.
At least two phases

22. All transformers step voltage up or down by...
Four times less than that of the secondary.
Squirrel-cage rotor.
800 volts.
Inductance.

23. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Isolation transformer.
Squirrel-cage rotor.
Electro-magnetism for their operation.
At least two phases

24. 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?
The chest should rise or inflate.
Inductance.
Check to make sure that the victim is not still in contact with the electricity.
75 turns.

25. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
3 -979 Volts.
Cut around clothing that has adhered to the burned area.
Alternating current.
Disconnect the frame-grounding conductor.

26. The secondary windings on a 10:1 step-down transformer will have a wire size...
Full-load - three-phase voltage.
Larger than that found in the primary winding.
X.
The capacitors should be discharged.

27. Compared to the secondary of a loaded - step-down transformer - the primary has...
Inductance.
Lower current and higher voltage.
Reverse any two-phase leads.
No.6 AWG.

28. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
Provides single-phase power to smaller loads such as lights - heaters - etc.
60 Hertz
Inductance.

29. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
2000 watts
150 turns.
Short-circuited after power has been removed.
Carotid pulse - which is located in the neck next to the Adam's apple.

30. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
5:1
An electromagnet.
Zero amps.
Inductance.

31. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Inductance.
75 turns.
An electromagnet.
The capacitors should be discharged.

32. What type motor is a wound-rotor induction motor?
200 volts AC.
Four times less than that of the secondary.
Shunted and taped
A.C.

33. Not a symptom of electrical shock?.
Provides single-phase power to smaller loads such as lights - heaters - etc.
They should be made by the same manufacturer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Hyperventilation.

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

35. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
60 cycles per second (60 Hertz).
100 volts.
They should be made by the same manufacturer.
Lower current and higher voltage.

36. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Short-circuited after power has been removed.
Isolation transformer.
3 -979 Volts.

37. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
No.6 AWG.
Cut around clothing that has adhered to the burned area.
Two speeds

38. The standard frequency of alternating current used at a mine is...
Current changing constantly in magnitude and periodically in direction.
Larger than that found in the primary winding.
Squirrel-cage rotor.
60 Hertz

39. Which of the following does a squirrel cage induction motor have?
Stator windings.
H terminals.
5:1
800 volts.

40. A control power transformer...
A grounding resistor.
Provides single-phase power to smaller loads such as lights - heaters - etc.
They should be made by the same manufacturer.
2000 watts

41. The primary function of a power transformer is to provide...
600 volts.
Full-load - three-phase voltage.
Disconnect the frame-grounding conductor.
Nearly constant.

42. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
At least two phases
12 to 15 times a minute.
Two speeds
7 -630 volts.

43. A solenoid coil is...
Stator windings.
Kilovolt ampere (KVA).
H terminals.
An electromagnet.

44. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Two speeds
2000 watts
The sum of the two capacitors.

45. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Short-circuited after power has been removed.
Second-degree burn.
Clamp-on ammeter.
A step-up transformer.

46. Operating coils - motors - transformers - relays and solenoids depend upon...
It provides good speed control.
A device used to store electrical energy.
Electro-magnetism for their operation.
Capacitance.

47. The property of an electrical circuit that opposes any change in voltage is called...
No.6 AWG.
H terminals.
Capacitance.
Provides single-phase power to smaller loads such as lights - heaters - etc.

48. How do you change the direction of a 3-phase AC motor?
Provides single-phase power to smaller loads such as lights - heaters - etc.
Reverse any two-phase leads.
60 Hertz
The motor rotation is reversed.

49. 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?
Clamp-on ammeter.
75 turns.
25 feet.
A device used to store electrical energy.

50. Not true about AC power?
It provides good speed control.
277 volts.
H terminals.
100 volts.