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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. 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.
100 volts.
No.6 AWG.
Provides single-phase power to smaller loads such as lights - heaters - etc.

2. Not a symptom of electrical shock?.
A grounding resistor.
H terminals.
Hyperventilation.
They must be installed at least 7 feet above the ground.

3. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
100 volts.
Clamp-on ammeter.
Allow for metering voltage and Current.

4. The primary function of a power transformer is to provide...
Grounded phase and ground fault devices were not operating.
5:1
Carotid pulse - which is located in the neck next to the Adam's apple.
Full-load - three-phase voltage.

5. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
800 volts.
Reverse any two-phase leads.
An electrical shock hazard may exist.

6. Alternating current may be defined as...
An electrical shock hazard may exist.
It provides good speed control.
Continuous.
Current that changes constantly in magnitude and periodically in direction.

7. 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.
5:1
H terminals.
Stator windings.

8. Compared to the secondary of a loaded - step-down transformer - the primary has...
They should be made by the same manufacturer.
Potential transformer.
Two speeds
Lower current and higher voltage

9. 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?
Check to make sure that the victim is not still in contact with the electricity.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Four times less than that of the secondary.
600 volts.

10. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Four times less than that of the secondary.
Shunted and taped
Allow for metering voltage and Current.
800 volts.

11. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Provides single-phase power to smaller loads such as lights - heaters - etc.
12 to 15 times a minute.
Full-load - three-phase voltage.

12. The transformer used only to measure voltage is a...
The sum of the two capacitors.
Current changing constantly in magnitude and periodically in direction.
Potential transformer.
Draw less current.

13. A burn causing a blister is classified as a...
Carotid pulse - which is located in the neck next to the Adam's apple.
Second-degree burn.
The capacitors should be discharged.
Current that changes constantly in magnitude and periodically in direction.

14. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
5:1
100 turns.
An electrical shock hazard may exist.

15. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
3 -979 Volts.
200 volts AC.
Potential transformer.

16. The combined capacitance of two capacitors in parallel is...
3 -979 Volts.
The sum of the two capacitors.
A device used to store electrical energy.
480 volts.

17. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Nearly constant.
They should be made by the same manufacturer.
7 -630 volts.
1 amp.

18. 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?
100 volts.
200 volts AC.
At least two phases
Provides single-phase power to smaller loads such as lights - heaters - etc.

19. A transformer with a 1:1 ratio is usually a (an)...
The chest should rise or inflate.
Isolation transformer.
277 volts.
Clamp-on ammeter.

20. 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.
3 -979 Volts.
No.6 AWG.
Full-load - three-phase voltage.

21. The property of an electrical circuit that opposes any change in voltage is called...
Hyperventilation.
15 feet off the ground.
Capacitance.
The capacitors should be discharged.

22. 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?
Capacitance.
75 turns.
Inductance.
Current changing constantly in magnitude and periodically in direction.

23. 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.
At the source transformer.
7 -630 volts.
5:1

24. The standard frequency of power supplied by the power company is...
150 turns.
The current will read zero.
A grounding resistor.
60 cycles per second (60 Hertz).

25. 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?
X.
75 turns.
H terminals.
Two speeds

26. Current in an AC circuit may be measured by...
A.C.
At the source transformer.
Capacitance.
Clamp-on ammeter.

27. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
277 volts.
Current that changes constantly in magnitude and periodically in direction.
They must be installed at least 7 feet above the ground.

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

29. What type motor is a wound-rotor induction motor?
277 volts.
A.C.
Shunted and taped
Carotid pulse - which is located in the neck next to the Adam's apple.

30. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
60 cycles per second (60 Hertz).
Reverse any two-phase leads.
The motor rotation is reversed.

31. Not true about AC power?
100 volts.
It provides good speed control.
15 feet off the ground.
The sum of the two capacitors.

32. Which of the following does a squirrel cage induction motor have?
Zero amps.
Isolation transformer.
Short-circuited after power has been removed.
Stator windings.

33. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
3 -979 Volts.
Tied together
25 feet.
Hyperventilation.

34. Define alternating current...
Cut around clothing that has adhered to the burned area.
Inductance.
Current changing constantly in magnitude and periodically in direction.
Grounded phase and ground fault devices were not operating.

35. 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...
Potential transformer.
X.
Carotid pulse - which is located in the neck next to the Adam's apple.
Draw less current.

36. When not connected to a load - the secondary leads of a current transformer should be...
75 turns.
Shunted and taped
2000 watts
It provides good speed control.

37. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
No.6 AWG.
Stator windings.
Transformers.

38. Current transformers - or CT's - are used to...
A.C.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
25 feet.
Short-circuited after power has been removed.

39. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
7 -630 volts.
60 Hertz
Two speeds
Draw less current.

40. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Tied together
Provides single-phase power to smaller loads such as lights - heaters - etc.
Draw less current.
15 feet off the ground.

41. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Inductance.
Carotid pulse - which is located in the neck next to the Adam's apple.
At the source transformer.

42. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Allow for metering voltage and Current.
Larger than that found in the primary winding.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
They should be made by the same manufacturer.

43. The primary leads of a single-phase transformer should be connected to the...
H terminals.
100 volts.
Two speeds
An electromagnet.

44. 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.
100 turns.
1 amp.
It provides good speed control.

45. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Check to make sure that the victim is not still in contact with the electricity.
The sum of the two capacitors.
Two speeds
Lower current and higher voltage.

46. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Reverse its rotation.
25 feet.
Disconnect the frame-grounding conductor.
Alternating current.

47. At what rate should mouth-to-mouth resuscitation be applied?
Second-degree burn.
12 to 15 times a minute.
Isolation transformer.
Carotid pulse - which is located in the neck next to the Adam's apple.

48. 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...
Current that changes constantly in magnitude and periodically in direction.
100 volts.
An electromagnet.
They should be made by the same manufacturer.

49. What is a capacitor?
No.6 AWG.
A device used to store electrical energy.
5:1.
800 volts.

50. All transformers step voltage up or down by...
A.C.
12 to 15 times a minute.
5:1
Inductance.