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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. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Isolation transformer.
Second-degree burn.
A grounding resistor.
Hyperventilation.

2. Which of the following does a squirrel cage induction motor have?
Stator windings.
Hyperventilation.
480 volts.
Zero amps.

3. 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?
Short-circuited after power has been removed.
It provides good speed control.
600 volts.
H terminals.

4. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
60 Hertz
They must be installed at least 7 feet above the ground.
Check to make sure that the victim is not still in contact with the electricity.
7 -630 volts.

5. What should the duty rating of a grounding resistor be?
The capacitors should be discharged.
It provides good speed control.
5:1
Continuous.

6. Compared to the secondary of a loaded - step-down transformer - the primary has...
2000 watts
A grounding resistor.
100 volts.
Lower current and higher voltage.

7. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
H terminals.
X.
At the source transformer.
The current will read zero.

8. 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.
At the source transformer.
Cut around clothing that has adhered to the burned area.
480 volts.

9. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Squirrel-cage rotor.
Current that changes constantly in magnitude and periodically in direction.
The motor rotation is reversed.

10. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Short-circuited after power has been removed.
Electro-magnetism for their operation.
1 amp.
150 turns.

11. How do you change the direction of a 3-phase AC motor?
The chest should rise or inflate.
The sum of the two capacitors.
Reverse any two-phase leads.
15 feet off the ground.

12. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
They must be installed at least 7 feet above the ground.
A grounding resistor.
The sum of the two capacitors.

13. The speed of an alternating current - squirrel-cage induction motor is...
Carotid pulse - which is located in the neck next to the Adam's apple.
Nearly constant.
12 to 15 times a minute.
The sum of the two capacitors.

14. What steps up or steps down AC voltage?
Transformer
Reverse its rotation.
60 cycles per second (60 Hertz).
Current changing constantly in magnitude and periodically in direction.

15. 460 volts AC is required to operate two motors - one connected in single-phase and the other connected in three-phase. The three-phase motor will...
277 volts.
Zero amps.
Draw less current.
Derive a neutral for grounding purposes.

16. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
12 to 15 times a minute.
No.6 AWG.
The motor rotation is reversed.
200 volts AC.

17. A wound-rotor induction motor has all the following EXCEPT...
2000 watts
Provides single-phase power to smaller loads such as lights - heaters - etc.
Squirrel-cage rotor.
Reverse any two-phase leads.

18. 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...
Four times less than that of the secondary.
Continuous.
200 volts AC.
100 volts.

19. 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?
100 turns.
Larger than that found in the primary winding.
Check to make sure that the victim is not still in contact with the electricity.
Disconnect the frame-grounding conductor.

20. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
At least two phases
15 feet off the ground.
480 volts.
Potential transformer.

21. When not connected to a load - the secondary leads of a current transformer should be...
Draw less current.
Shunted and taped
Larger than that found in the primary winding.
Transformers.

22. 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...
A.C.
Transformer
Alternating current.
Tied together

23. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Lower current and higher voltage
The capacitors should be discharged.
1 amp.

24. 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.
15 feet off the ground.
A device used to store electrical energy.
5:1
The current will read zero.

25. The property of an electrical circuit that opposes any change in voltage is called...
1 amp.
60 Hertz
Electro-magnetism for their operation.
Capacitance.

26. Compared to the secondary of a loaded - step-down transformer - the primary has...
3 -979 Volts.
Lower current and higher voltage
Second-degree burn.
The chest should rise or inflate.

27. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Zero amps.
They should be made by the same manufacturer.
Reverse its rotation.

28. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
Grounded phase and ground fault devices were not operating.
Circuit Breaker.
3 -979 Volts.

29. All transformers step voltage up or down by...
100 turns.
2000 watts
Disconnect the frame-grounding conductor.
Inductance.

30. The size of a transformer is measured in...
It provides good speed control.
Kilovolt ampere (KVA).
Capacitance.
12 to 15 times a minute.

31. What is the first step to be followed in aiding a victim of electrical shock?
Current that changes constantly in magnitude and periodically in direction.
The motor rotation is reversed.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Check to make sure that the victim is not still in contact with the electricity.

32. Not a symptom of electrical shock?.
Capacitance.
1 amp.
Nearly constant.
Hyperventilation.

33. The secondary windings on a 10:1 step-down transformer will have a wire size...
Draw less current.
Larger than that found in the primary winding.
Isolation transformer.
Reverse its rotation.

34. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
3 -979 Volts.
A step-up transformer.
Four times less than that of the secondary.

35. A transformer with a 1:1 ratio is usually a (an)...
15 feet off the ground.
Derive a neutral for grounding purposes.
Isolation transformer.
Current changing constantly in magnitude and periodically in direction.

36. What type motor is a wound-rotor induction motor?
3 -979 Volts.
75 turns.
Zero amps.
A.C.

37. If any two-phase wires are reversed on a three-phase motor - the motor will...
Inductance.
Reverse its rotation.
Four times less than that of the secondary.
The current will read zero.

38. 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...
Disconnect the frame-grounding conductor.
Draw less current.
Check to make sure that the victim is not still in contact with the electricity.
2000 watts

39. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Cut around clothing that has adhered to the burned area.
Current that changes constantly in magnitude and periodically in direction.
An electrical shock hazard may exist.
Short-circuited after power has been removed.

40. Where should grounding resistors be located?
200 volts AC.
60 Hertz
At the source transformer.
Draw less current.

41. AC voltage is raised or lowered by means of...
Transformers.
Current changing constantly in magnitude and periodically in direction.
X.
A.C.

42. The property of an electric circuit that opposes any change in current is called...
Inductance.
The sum of the two capacitors.
150 turns.
100 volts.

43. Define alternating current...
Because less current flowing at high voltage causes less line loss per kilowatt.
Circuit Breaker.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Current changing constantly in magnitude and periodically in direction.

44. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Allow for metering voltage and Current.
Two speeds
5:1
Tied together

45. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
An electrical shock hazard may exist.
200 volts AC.
They should be made by the same manufacturer.
Grounded phase and ground fault devices were not operating.

46. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
At least two phases
Carotid pulse - which is located in the neck next to the Adam's apple.
277 volts.
H terminals.

47. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Provides single-phase power to smaller loads such as lights - heaters - etc.
480 volts.
At the source transformer.

48. The combined capacitance of two capacitors in parallel is...
15 feet off the ground.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The sum of the two capacitors.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

49. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
X.
The current will read zero.
An electromagnet.
1 amp.

50. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
480 volts.
Clamp-on ammeter.
The sum of the two capacitors.
2000 watts