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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. AC voltage is raised or lowered by means of...
Shunted and taped
Lower current and higher voltage.
Transformers.
Cut around clothing that has adhered to the burned area.

2. A transformer with a 1:1 ratio is usually a (an)...
5:1
They should be made by the same manufacturer.
5:1.
Isolation transformer.

3. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
200 volts AC.
Check to make sure that the victim is not still in contact with the electricity.
277 volts.

4. The combined capacitance of two capacitors in parallel is...
Grounded phase and ground fault devices were not operating.
5:1.
The sum of the two capacitors.
Short-circuited after power has been removed.

5. 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...
At the source transformer.
Carotid pulse - which is located in the neck next to the Adam's apple.
The sum of the two capacitors.
Draw less current.

6. How do you change the direction of a 3-phase AC motor?
Draw less current.
Reverse any two-phase leads.
Because less current flowing at high voltage causes less line loss per kilowatt.
An electromagnet.

7. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
277 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
15 feet off the ground.
Check to make sure that the victim is not still in contact with the electricity.

8. 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
The motor rotation is reversed.
150 turns.
Stator windings.

9. The main function of CT's and PT's on a main substation is to...
Full-load - three-phase voltage.
Allow for metering voltage and Current.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The capacitors should be discharged.

10. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
The chest should rise or inflate.
Allow for metering voltage and Current.
Provides single-phase power to smaller loads such as lights - heaters - etc.

11. 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.
25 feet.
7 -630 volts.
5:1.
Carotid pulse - which is located in the neck next to the Adam's apple.

12. Operating coils - motors - transformers - relays and solenoids depend upon...
Reverse its rotation.
Electro-magnetism for their operation.
Disconnect the frame-grounding conductor.
Clamp-on ammeter.

13. 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.
2000 watts
Tied together
Capacitance.

14. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Clamp-on ammeter.
Grounded phase and ground fault devices were not operating.
Inductance.
It provides good speed control.

15. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
Hyperventilation.
Nearly constant.
An electromagnet.

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...
At least two phases
100 volts.
The motor rotation is reversed.
Larger than that found in the primary winding.

17. The speed of an alternating current - squirrel-cage induction motor is...
15 feet off the ground.
60 cycles per second (60 Hertz).
Provides single-phase power to smaller loads such as lights - heaters - etc.
Nearly constant.

18. Not a symptom of electrical shock?.
Hyperventilation.
2000 watts
Carotid pulse - which is located in the neck next to the Adam's apple.
Shunted and taped

19. The secondary windings on a 10:1 step-down transformer will have a wire size...
Current that changes constantly in magnitude and periodically in direction.
They should be made by the same manufacturer.
An electromagnet.
Larger than that found in the primary winding.

20. All transformers step voltage up or down by...
Lower current and higher voltage.
480 volts.
Clamp-on ammeter.
Inductance.

21. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
Short-circuited after power has been removed.
An electrical shock hazard may exist.
Transformers.

22. Alternating current may be defined as...
At the source transformer.
Circuit Breaker.
Current that changes constantly in magnitude and periodically in direction.
1 amp.

23. 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
The chest should rise or inflate.
277 volts.
Alternating current.

24. What type of 3-phase AC motor is used most often around a mine?
Capacitance.
Squirrel-cage induction motor.
800 volts.
15 feet off the ground.

25. A wound-rotor induction motor has all the following EXCEPT...
Draw less current.
Squirrel-cage rotor.
At least two phases
An electromagnet.

26. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Allow for metering voltage and Current.
Squirrel-cage induction motor.
1 amp.
The chest should rise or inflate.

27. 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?
Carotid pulse - which is located in the neck next to the Adam's apple.
200 volts AC.
800 volts.
60 Hertz

28. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Reverse its rotation.
Grounded phase and ground fault devices were not operating.
Four times less than that of the secondary.
Zero amps.

29. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Grounded phase and ground fault devices were not operating.
Stator windings.
At least two phases
Inductance.

30. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
277 volts.
H terminals.
Hyperventilation.

31. What is a capacitor?
The chest should rise or inflate.
A device used to store electrical energy.
Inductance.
Kilovolt ampere (KVA).

32. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
3 -979 Volts.
5:1
Disconnect the frame-grounding conductor.
X.

33. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Alternating current.
Short-circuited after power has been removed.
100 volts.
They should be made by the same manufacturer.

34. At what rate should mouth-to-mouth resuscitation be applied?
Grounded phase and ground fault devices were not operating.
At least two phases
12 to 15 times a minute.
Derive a neutral for grounding purposes.

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

36. A burn causing a blister is classified as a...
At the source transformer.
75 turns.
Second-degree burn.
Four times less than that of the secondary.

37. 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.C.
Transformer
60 Hertz
100 turns.

38. The transformer used only to measure voltage is a...
Inductance.
The chest should rise or inflate.
Potential transformer.
2000 watts

39. Compared to the secondary of a loaded - step-down transformer - the primary has...
150 turns.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Lower current and higher voltage.
H terminals.

40. Which of the following does a squirrel cage induction motor have?
Stator windings.
The capacitors should be discharged.
Isolation transformer.
25 feet.

41. Compared to the secondary of a loaded - step-down transformer - the primary has...
7 -630 volts.
Squirrel-cage rotor.
Check to make sure that the victim is not still in contact with the electricity.
Lower current and higher voltage

42. What is the first step to be followed in aiding a victim of electrical shock?
Check to make sure that the victim is not still in contact with the electricity.
Hyperventilation.
Squirrel-cage induction motor.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

43. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Current changing constantly in magnitude and periodically in direction.
Transformer
Lower current and higher voltage
The motor rotation is reversed.

44. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
A grounding resistor.
7 -630 volts.
5:1
Zero amps.

45. What is the danger when working around capacitors?
Reverse its rotation.
An electrical shock hazard may exist.
Full-load - three-phase voltage.
A grounding resistor.

46. Not true about AC power?
It provides good speed control.
Kilovolt ampere (KVA).
Isolation transformer.
Inductance.

47. Current that changes periodically in direction is...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Four times less than that of the secondary.
H terminals.
Alternating current.

48. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
600 volts.
It provides good speed control.
60 Hertz

49. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Capacitance.
Hyperventilation.
Current that changes constantly in magnitude and periodically in direction.

50. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Circuit Breaker.
Potential transformer.
60 cycles per second (60 Hertz).
Zero amps.