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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. What is a capacitor?
25 feet.
Clamp-on ammeter.
A device used to store electrical energy.
An electromagnet.

2. 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.
200 volts AC.
Hyperventilation.
Continuous.

3. A transformer with a 1:1 ratio is usually a (an)...
Four times less than that of the secondary.
Isolation transformer.
The current will read zero.
60 Hertz

4. 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.
It provides good speed control.
5:1
The motor rotation is reversed.

5. Alternating current may be defined as...
Allow for metering voltage and Current.
60 cycles per second (60 Hertz).
25 feet.
Current that changes constantly in magnitude and periodically in direction.

6. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
It provides good speed control.
The chest should rise or inflate.
Reverse any two-phase leads.

7. 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.
Draw less current.
60 cycles per second (60 Hertz).
They should be made by the same manufacturer.

8. 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...
Draw less current.
Larger than that found in the primary winding.
100 turns.
Lower current and higher voltage.

9. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Disconnect the frame-grounding conductor.
Isolation transformer.
60 cycles per second (60 Hertz).

10. The standard frequency of power supplied by the power company is...
It provides good speed control.
A step-up transformer.
60 cycles per second (60 Hertz).
Check to make sure that the victim is not still in contact with the electricity.

11. Which of the following does a squirrel cage induction motor have?
The capacitors should be discharged.
H terminals.
Stator windings.
A grounding resistor.

12. All transformers step voltage up or down by...
Inductance.
The capacitors should be discharged.
The sum of the two capacitors.
Check to make sure that the victim is not still in contact with the electricity.

13. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
Check to make sure that the victim is not still in contact with the electricity.
Current that changes constantly in magnitude and periodically in direction.
Provides single-phase power to smaller loads such as lights - heaters - etc.

14. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Isolation transformer.
Grounded phase and ground fault devices were not operating.
Stator windings.
An electromagnet.

15. What is the first step to be followed in aiding a victim of electrical shock?
Alternating current.
At least two phases
A.C.
Check to make sure that the victim is not still in contact with the electricity.

16. 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...
The capacitors should be discharged.
The sum of the two capacitors.
Cut around clothing that has adhered to the burned area.
100 volts.

17. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
The chest should rise or inflate.
Two speeds
Circuit Breaker.
Grounded phase and ground fault devices were not operating.

18. 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.
Kilovolt ampere (KVA).
Allow for metering voltage and Current.
Capacitance.
5:1

19. The property of an electric circuit that opposes any change in current is called...
Inductance.
Full-load - three-phase voltage.
75 turns.
Isolation transformer.

20. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
5:1
Nearly constant.
7 -630 volts.

21. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A grounding resistor.
Larger than that found in the primary winding.
Second-degree burn.
Transformers.

22. What steps up or steps down AC voltage?
277 volts.
A step-up transformer.
Transformer
Two speeds

23. 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.
Lower current and higher voltage.
Current changing constantly in magnitude and periodically in direction.
The capacitors should be discharged.

24. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Hyperventilation.
Nearly constant.
Disconnect the frame-grounding conductor.
Provides single-phase power to smaller loads such as lights - heaters - etc.

25. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
They should be made by the same manufacturer.
No.6 AWG.
150 turns.
Squirrel-cage rotor.

26. What should the duty rating of a grounding resistor be?
At the source transformer.
Continuous.
5:1
75 turns.

27. The primary function of a power transformer is to provide...
Transformers.
Full-load - three-phase voltage.
A device used to store electrical energy.
60 cycles per second (60 Hertz).

28. 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?
100 volts.
3 -979 Volts.
Grounded phase and ground fault devices were not operating.
Zero amps.

29. The standard frequency of alternating current used at a mine is...
277 volts.
60 Hertz
A step-up transformer.
Alternating current.

30. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
1 amp.
600 volts.
100 volts.

31. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
5:1.
The sum of the two capacitors.
Kilovolt ampere (KVA).
480 volts.

32. 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?
Circuit Breaker.
600 volts.
X.
Shunted and taped

33. The size of a transformer is measured in...
Kilovolt ampere (KVA).
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.
3 -979 Volts.

34. Compared to the secondary of a loaded - step-down transformer - the primary has...
75 turns.
A grounding resistor.
60 Hertz
Lower current and higher voltage.

35. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Transformer
Clamp-on ammeter.
It provides good speed control.

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

37. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
They should be made by the same manufacturer.
Zero amps.
5:1
They must be installed at least 7 feet above the ground.

38. A solenoid coil is...
At the source transformer.
An electromagnet.
480 volts.
800 volts.

39. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
Capacitance.
Cut around clothing that has adhered to the burned area.
15 feet off the ground.

40. Current transformers - or CT's - are used to...
A grounding resistor.
15 feet off the ground.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Provides single-phase power to smaller loads such as lights - heaters - etc.

41. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
Current changing constantly in magnitude and periodically in direction.
Derive a neutral for grounding purposes.
A step-up transformer.

42. Not an acceptable method for the installations of surface transformers?
Provides single-phase power to smaller loads such as lights - heaters - etc.
They must be installed at least 7 feet above the ground.
Nearly constant.
At the source transformer.

43. 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?
1 amp.
Circuit Breaker.
Draw less current.
100 turns.

44. 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?
A.C.
Full-load - three-phase voltage.
Kilovolt ampere (KVA).
75 turns.

45. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Inductance.
They should be made by the same manufacturer.
3 -979 Volts.
A step-up transformer.

46. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Draw less current.
Hyperventilation.

47. AC voltage is raised or lowered by means of...
Transformers.
15 feet off the ground.
Current changing constantly in magnitude and periodically in direction.
At least two phases

48. The purpose of a zig-zag transformer is to...
Clamp-on ammeter.
Nearly constant.
A device used to store electrical energy.
Derive a neutral for grounding purposes.

49. The transformer used only to measure voltage is a...
200 volts AC.
Potential transformer.
A device used to store electrical energy.
25 feet.

50. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
H terminals.
25 feet.
The capacitors should be discharged.
A grounding resistor.