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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. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Current that changes constantly in magnitude and periodically in direction.
15 feet off the ground.
Hyperventilation.
Inductance.

2. 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?
Disconnect the frame-grounding conductor.
Reverse any two-phase leads.
Inductance.
800 volts.

3. What is the first step to be followed in aiding a victim of electrical shock?
75 turns.
At least two phases
Clamp-on ammeter.
Check to make sure that the victim is not still in contact with the electricity.

4. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
A grounding resistor.
Allow for metering voltage and Current.
75 turns.

5. What type of 3-phase AC motor is used most often around a mine?
100 turns.
Squirrel-cage induction motor.
A.C.
Second-degree burn.

6. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
75 turns.
The chest should rise or inflate.
800 volts.
Draw less current.

7. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Transformers.
Squirrel-cage rotor.
2000 watts

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

9. 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?
Tied together
800 volts.
75 turns.
Current that changes constantly in magnitude and periodically in direction.

10. The speed of an alternating current - squirrel-cage induction motor is...
A step-up transformer.
Nearly constant.
Derive a neutral for grounding purposes.
The capacitors should be discharged.

11. A burn causing a blister is classified as a...
An electromagnet.
5:1
Squirrel-cage induction motor.
Second-degree burn.

12. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
The capacitors should be discharged.
A grounding resistor.
75 turns.
A device used to store electrical energy.

13. The secondary windings on a 10:1 step-down transformer will have a wire size...
Because less current flowing at high voltage causes less line loss per kilowatt.
Tied together
Check to make sure that the victim is not still in contact with the electricity.
Larger than that found in the primary winding.

14. The transformer used only to measure voltage is a...
7 -630 volts.
Potential transformer.
Draw less current.
Squirrel-cage rotor.

15. 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.
The sum of the two capacitors.
A step-up transformer.
Electro-magnetism for their operation.

16. The property of an electric circuit that opposes any change in current is called...
Squirrel-cage induction motor.
Inductance.
75 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.

17. Alternating current may be defined as...
60 Hertz
480 volts.
Current that changes constantly in magnitude and periodically in direction.
Inductance.

18. What is a capacitor?
The chest should rise or inflate.
A device used to store electrical energy.
They must be installed at least 7 feet above the ground.
Continuous.

19. High voltage is used to transmit power over long distances...
Larger than that found in the primary winding.
Because less current flowing at high voltage causes less line loss per kilowatt.
Second-degree burn.
The current will read zero.

20. What should the duty rating of a grounding resistor be?
Draw less current.
The chest should rise or inflate.
Because less current flowing at high voltage causes less line loss per kilowatt.
Continuous.

21. Compared to the secondary of a loaded - step-down transformer - the primary has...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Kilovolt ampere (KVA).
75 turns.
Lower current and higher voltage

22. 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?
Derive a neutral for grounding purposes.
3 -979 Volts.
Cut around clothing that has adhered to the burned area.
150 turns.

23. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
They should be made by the same manufacturer.
277 volts.
2000 watts
A.C.

24. AC voltage is raised or lowered by means of...
25 feet.
Transformers.
Carotid pulse - which is located in the neck next to the Adam's apple.
Potential transformer.

25. 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 device used to store electrical energy.
The capacitors should be discharged.
100 turns.
Squirrel-cage rotor.

26. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
The sum of the two capacitors.
Grounded phase and ground fault devices were not operating.
Kilovolt ampere (KVA).
Because less current flowing at high voltage causes less line loss per kilowatt.

27. What type motor is a wound-rotor induction motor?
100 turns.
Larger than that found in the primary winding.
A.C.
Cut around clothing that has adhered to the burned area.

28. Current that changes periodically in direction is...
5:1.
They should be made by the same manufacturer.
Lower current and higher voltage
Alternating current.

29. Three-phase AC underground cables must be provided with overcurrent protection using a...
Carotid pulse - which is located in the neck next to the Adam's apple.
1 amp.
60 cycles per second (60 Hertz).
Circuit Breaker.

30. Not an acceptable method for the installations of surface transformers?
Derive a neutral for grounding purposes.
They must be installed at least 7 feet above the ground.
Cut around clothing that has adhered to the burned area.
Allow for metering voltage and Current.

31. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
7 -630 volts.
Short-circuited after power has been removed.
Alternating current.
Squirrel-cage induction motor.

32. The size of a transformer is measured in...
Kilovolt ampere (KVA).
5:1
Tied together
An electromagnet.

33. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
Potential transformer.
The motor rotation is reversed.
Short-circuited after power has been removed.

34. 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...
An electromagnet.
They should be made by the same manufacturer.
Tied together
X.

35. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
X.
Derive a neutral for grounding purposes.
Short-circuited after power has been removed.
2000 watts

36. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
600 volts.
Disconnect the frame-grounding conductor.
200 volts AC.

37. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
75 turns.
Current changing constantly in magnitude and periodically in direction.
Allow for metering voltage and Current.

38. The property of an electrical circuit that opposes any change in voltage is called...
Because less current flowing at high voltage causes less line loss per kilowatt.
1 amp.
Squirrel-cage rotor.
Capacitance.

39. Operating coils - motors - transformers - relays and solenoids depend upon...
Full-load - three-phase voltage.
12 to 15 times a minute.
Electro-magnetism for their operation.
Squirrel-cage induction motor.

40. To protect against over-current in a three-phase circuit over-current protection must be provided for...
H terminals.
60 cycles per second (60 Hertz).
7 -630 volts.
At least two phases

41. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Kilovolt ampere (KVA).
75 turns.
Draw less current.

42. A transformer with a 1:1 ratio is usually a (an)...
600 volts.
Isolation transformer.
100 volts.
75 turns.

43. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
A device used to store electrical energy.
Transformer
At the source transformer.

44. All transformers step voltage up or down by...
100 turns.
Allow for metering voltage and Current.
Inductance.
Draw less current.

45. 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?
Second-degree burn.
600 volts.
Zero amps.
The sum of the two capacitors.

46. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
60 cycles per second (60 Hertz).
2000 watts
Larger than that found in the primary winding.

47. 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.
800 volts.
15 feet off the ground.
5:1
Two speeds

48. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Shunted and taped
A step-up transformer.
They should be made by the same manufacturer.
Clamp-on ammeter.

49. The main function of CT's and PT's on a main substation is to...
Because less current flowing at high voltage causes less line loss per kilowatt.
5:1.
Stator windings.
Allow for metering voltage and Current.

50. 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?
The chest should rise or inflate.
Reverse its rotation.
Kilovolt ampere (KVA).
3 -979 Volts.