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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. At what rate should mouth-to-mouth resuscitation be applied?
277 volts.
12 to 15 times a minute.
5:1
75 turns.

2. 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...
The capacitors should be discharged.
5:1
Tied together
Transformer

3. 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...
100 volts.
Reverse any two-phase leads.
The motor rotation is reversed.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

4. Where should grounding resistors be located?
At the source transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The motor rotation is reversed.
150 turns.

5. Current that changes periodically in direction is...
At least two phases
Alternating current.
75 turns.
A step-up transformer.

6. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
No.6 AWG.
Lower current and higher voltage
Potential transformer.
Disconnect the frame-grounding conductor.

7. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
75 turns.
An electromagnet.
Inductance.
The motor rotation is reversed.

8. What should the duty rating of a grounding resistor be?
Carotid pulse - which is located in the neck next to the Adam's apple.
Continuous.
1 amp.
Circuit Breaker.

9. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
A step-up transformer.
Lower current and higher voltage.
X.

10. 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.
5:1.
Transformer
Clamp-on ammeter.
5:1

11. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
2000 watts
Because less current flowing at high voltage causes less line loss per kilowatt.
Short-circuited after power has been removed.
They must be installed at least 7 feet above the ground.

12. 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?
Electro-magnetism for their operation.
A.C.
150 turns.
Allow for metering voltage and Current.

13. The speed of an alternating current - squirrel-cage induction motor is...
1 amp.
Nearly constant.
Lower current and higher voltage.
Reverse any two-phase leads.

14. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Reverse its rotation.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Four times less than that of the secondary.
Reverse any two-phase leads.

15. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
X.
The chest should rise or inflate.
Draw less current.
5:1.

16. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
The sum of the two capacitors.
Second-degree burn.
Current that changes constantly in magnitude and periodically in direction.
No.6 AWG.

17. A burn causing a blister is classified as a...
Second-degree burn.
Alternating current.
25 feet.
No.6 AWG.

18. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Because less current flowing at high voltage causes less line loss per kilowatt.
Four times less than that of the secondary.
Potential transformer.
Short-circuited after power has been removed.

19. 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?
Lower current and higher voltage.
Hyperventilation.
5:1.
3 -979 Volts.

20. 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.
12 to 15 times a minute.
Reverse any two-phase leads.
800 volts.

21. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
A.C.
Second-degree burn.
Provides single-phase power to smaller loads such as lights - heaters - etc.

22. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Larger than that found in the primary winding.
480 volts.
Nearly constant.
5:1

23. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
The capacitors should be discharged.
H terminals.
Zero amps.

24. A transformer with a 1:1 ratio is usually a (an)...
Potential transformer.
A device used to store electrical energy.
An electromagnet.
Isolation transformer.

25. Which of the following does a squirrel cage induction motor have?
The motor rotation is reversed.
Stator windings.
A device used to store electrical energy.
A grounding resistor.

26. To protect against over-current in a three-phase circuit over-current protection must be provided for...
A device used to store electrical energy.
X.
Disconnect the frame-grounding conductor.
At least two phases

27. What is a capacitor?
75 turns.
1 amp.
480 volts.
A device used to store electrical energy.

28. A control power transformer...
Carotid pulse - which is located in the neck next to the Adam's apple.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Lower current and higher voltage.
75 turns.

29. 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?
Larger than that found in the primary winding.
It provides good speed control.
Disconnect the frame-grounding conductor.
75 turns.

30. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Check to make sure that the victim is not still in contact with the electricity.
Alternating current.
75 turns.

31. The primary leads of a single-phase transformer should be connected to the...
H terminals.
Short-circuited after power has been removed.
Four times less than that of the secondary.
A.C.

32. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Squirrel-cage rotor.
Tied together
100 volts.
Grounded phase and ground fault devices were not operating.

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

34. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
The chest should rise or inflate.
The capacitors should be discharged.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

35. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Squirrel-cage rotor.
60 Hertz
277 volts.
The current will read zero.

36. 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?
200 volts AC.
A.C.
H terminals.
Squirrel-cage rotor.

37. The purpose of a zig-zag transformer is to...
Check to make sure that the victim is not still in contact with the electricity.
Derive a neutral for grounding purposes.
200 volts AC.
7 -630 volts.

38. 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?
A device used to store electrical energy.
An electromagnet.
100 turns.
12 to 15 times a minute.

39. What steps up or steps down AC voltage?
It provides good speed control.
2000 watts
Stator windings.
Transformer

40. The property of an electric circuit that opposes any change in current is called...
Inductance.
Zero amps.
X.
2000 watts

41. 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.
The motor rotation is reversed.
100 turns.
Current changing constantly in magnitude and periodically in direction.

42. High voltage is used to transmit power over long distances...
Shunted and taped
A grounding resistor.
Because less current flowing at high voltage causes less line loss per kilowatt.
2000 watts

43. 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...
They should be made by the same manufacturer.
Draw less current.
Isolation transformer.
480 volts.

44. Not true about AC power?
Larger than that found in the primary winding.
Draw less current.
It provides good speed control.
1 amp.

45. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
A grounding resistor.
Larger than that found in the primary winding.
Four times less than that of the secondary.

46. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
It provides good speed control.
Continuous.
7 -630 volts.
Draw less current.

47. The transformer used only to measure voltage is a...
Potential transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Clamp-on ammeter.
Alternating current.

48. The size of a transformer is measured in...
Tied together
Current that changes constantly in magnitude and periodically in direction.
Kilovolt ampere (KVA).
Full-load - three-phase voltage.

49. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
An electromagnet.
Larger than that found in the primary winding.
X.
Zero amps.

50. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
Circuit Breaker.
Stator windings.
Transformer