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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. The primary function of a power transformer is to provide...
Lower current and higher voltage.
Full-load - three-phase voltage.
A device used to store electrical energy.
200 volts AC.

2. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
It provides good speed control.
7 -630 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
15 feet off the ground.

3. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Lower current and higher voltage
7 -630 volts.
600 volts.
Two speeds

4. What type motor is a wound-rotor induction motor?
60 cycles per second (60 Hertz).
Full-load - three-phase voltage.
A.C.
Carotid pulse - which is located in the neck next to the Adam's apple.

5. Current in an AC circuit may be measured by...
600 volts.
Clamp-on ammeter.
Reverse its rotation.
Larger than that found in the primary winding.

6. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The motor rotation is reversed.
3 -979 Volts.
Current that changes constantly in magnitude and periodically in direction.
15 feet off the ground.

7. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Hyperventilation.
It provides good speed control.
Two speeds
Tied together

8. What is the danger when working around capacitors?
Draw less current.
An electrical shock hazard may exist.
No.6 AWG.
Current that changes constantly in magnitude and periodically in direction.

9. Compared to the secondary of a loaded - step-down transformer - the primary has...
Draw less current.
Lower current and higher voltage
A grounding resistor.
At least two phases

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

11. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Because less current flowing at high voltage causes less line loss per kilowatt.
They should be made by the same manufacturer.
Shunted and taped
Inductance.

12. Current transformers - or CT's - are used to...
Potential transformer.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Current that changes constantly in magnitude and periodically in direction.
Transformer

13. The size of a transformer is measured in...
Larger than that found in the primary winding.
Capacitance.
Draw less current.
Kilovolt ampere (KVA).

14. Which of the following does a squirrel cage induction motor have?
12 to 15 times a minute.
600 volts.
100 turns.
Stator windings.

15. 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?
Larger than that found in the primary winding.
100 volts.
Electro-magnetism for their operation.
75 turns.

16. Not an acceptable method for the installations of surface transformers?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
They must be installed at least 7 feet above the ground.
5:1
Four times less than that of the secondary.

17. High voltage is used to transmit power over long distances...
Four times less than that of the secondary.
Because less current flowing at high voltage causes less line loss per kilowatt.
15 feet off the ground.
Zero amps.

18. 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?
Short-circuited after power has been removed.
Draw less current.
100 volts.
150 turns.

19. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
At least two phases
75 turns.
A step-up transformer.
A.C.

20. The transformer used only to measure voltage is a...
Potential transformer.
Squirrel-cage rotor.
A step-up transformer.
100 volts.

21. 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?
Circuit Breaker.
3 -979 Volts.
Lower current and higher voltage
5:1.

22. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
60 cycles per second (60 Hertz).
At the source transformer.
2000 watts

23. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Transformer
No.6 AWG.
Reverse any two-phase leads.
277 volts.

24. 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
5:1
600 volts.
5:1.

25. The property of an electrical circuit that opposes any change in voltage is called...
2000 watts
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Reverse any two-phase leads.
Capacitance.

26. 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?
277 volts.
100 volts.
25 feet.
800 volts.

27. Define alternating current...
Carotid pulse - which is located in the neck next to the Adam's apple.
Inductance.
Capacitance.
Current changing constantly in magnitude and periodically in direction.

28. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
3 -979 Volts.
5:1
75 turns.
The current will read zero.

29. If any two-phase wires are reversed on a three-phase motor - the motor will...
Grounded phase and ground fault devices were not operating.
Reverse its rotation.
480 volts.
3 -979 Volts.

30. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
Squirrel-cage induction motor.
Because less current flowing at high voltage causes less line loss per kilowatt.
Draw less current.

31. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
600 volts.
They must be installed at least 7 feet above the ground.
A.C.

32. The combined capacitance of two capacitors in parallel is...
Continuous.
The sum of the two capacitors.
25 feet.
75 turns.

33. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
It provides good speed control.
Disconnect the frame-grounding conductor.
5:1.
Check to make sure that the victim is not still in contact with the electricity.

34. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
Transformer
Lower current and higher voltage.
Current that changes constantly in magnitude and periodically in direction.

35. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Larger than that found in the primary winding.
An electrical shock hazard may exist.
X.
An electromagnet.

36. The standard frequency of power supplied by the power company is...
480 volts.
Continuous.
60 cycles per second (60 Hertz).
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

37. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
480 volts.
Larger than that found in the primary winding.
A.C.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

38. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Capacitance.
150 turns.
A step-up transformer.

39. 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.
The motor rotation is reversed.
5:1.
Disconnect the frame-grounding conductor.
An electromagnet.

40. What steps up or steps down AC voltage?
Zero amps.
Isolation transformer.
H terminals.
Transformer

41. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Clamp-on ammeter.
Carotid pulse - which is located in the neck next to the Adam's apple.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Four times less than that of the secondary.

42. The property of an electric circuit that opposes any change in current is called...
A step-up transformer.
Squirrel-cage rotor.
Because less current flowing at high voltage causes less line loss per kilowatt.
Inductance.

43. A solenoid coil is...
Cut around clothing that has adhered to the burned area.
An electromagnet.
Check to make sure that the victim is not still in contact with the electricity.
X.

44. Where should grounding resistors be located?
Draw less current.
A grounding resistor.
Two speeds
At the source transformer.

45. What is a capacitor?
60 Hertz
Derive a neutral for grounding purposes.
Lower current and higher voltage
A device used to store electrical energy.

46. Not a symptom of electrical shock?.
Hyperventilation.
100 volts.
75 turns.
60 Hertz

47. What should the duty rating of a grounding resistor be?
Inductance.
480 volts.
Continuous.
The chest should rise or inflate.

48. Three-phase AC underground cables must be provided with overcurrent protection using a...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Circuit Breaker.
1 amp.
Grounded phase and ground fault devices were not operating.

49. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Check to make sure that the victim is not still in contact with the electricity.
The chest should rise or inflate.
A.C.
The motor rotation is reversed.

50. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Transformers.
75 turns.
Potential transformer.