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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. 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?
An electrical shock hazard may exist.
A device used to store electrical energy.
75 turns.
Shunted and taped

2. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
75 turns.
Tied together
150 turns.

3. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
Kilovolt ampere (KVA).
An electromagnet.
They should be made by the same manufacturer.

4. Not a symptom of electrical shock?.
Hyperventilation.
Shunted and taped
480 volts.
25 feet.

5. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Squirrel-cage induction motor.
3 -979 Volts.
5:1.
Disconnect the frame-grounding conductor.

6. What is the danger when working around capacitors?
They should be made by the same manufacturer.
An electrical shock hazard may exist.
The capacitors should be discharged.
The chest should rise or inflate.

7. The primary function of a power transformer is to provide...
277 volts.
Draw less current.
Circuit Breaker.
Full-load - three-phase voltage.

8. A wound-rotor induction motor has all the following EXCEPT...
The current will read zero.
A.C.
Second-degree burn.
Squirrel-cage rotor.

9. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
Reverse its rotation.
Four times less than that of the secondary.
No.6 AWG.

10. Where should grounding resistors be located?
Second-degree burn.
At the source transformer.
Check to make sure that the victim is not still in contact with the electricity.
Nearly constant.

11. 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?
They must be installed at least 7 feet above the ground.
600 volts.
Second-degree burn.
100 turns.

12. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
A step-up transformer.
Zero amps.
100 volts.
Potential transformer.

13. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
A.C.
Inductance.
Inductance.

14. The main function of CT's and PT's on a main substation is to...
Transformer
Allow for metering voltage and Current.
Potential transformer.
1 amp.

15. How do you change the direction of a 3-phase AC motor?
Four times less than that of the secondary.
A device used to store electrical energy.
Because less current flowing at high voltage causes less line loss per kilowatt.
Reverse any two-phase leads.

16. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Shunted and taped
5:1
X.
Hyperventilation.

17. Not an acceptable method for the installations of surface transformers?
The motor rotation is reversed.
They must be installed at least 7 feet above the ground.
Squirrel-cage rotor.
Reverse any two-phase leads.

18. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Isolation transformer.
At least two phases
Check to make sure that the victim is not still in contact with the electricity.
Two speeds

19. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
They must be installed at least 7 feet above the ground.
Cut around clothing that has adhered to the burned area.
Reverse any two-phase leads.

20. What is the first step to be followed in aiding a victim of electrical shock?
Carotid pulse - which is located in the neck next to the Adam's apple.
Hyperventilation.
Check to make sure that the victim is not still in contact with the electricity.
277 volts.

21. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
1 amp.
Grounded phase and ground fault devices were not operating.
7 -630 volts.
No.6 AWG.

22. 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?
Clamp-on ammeter.
200 volts AC.
Provides single-phase power to smaller loads such as lights - heaters - etc.
60 Hertz

23. 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...
Kilovolt ampere (KVA).
A.C.
200 volts AC.
Draw less current.

24. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Full-load - three-phase voltage.
They should be made by the same manufacturer.
150 turns.
A grounding resistor.

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?
100 turns.
Lower current and higher voltage.
Carotid pulse - which is located in the neck next to the Adam's apple.
60 cycles per second (60 Hertz).

26. What is a capacitor?
A grounding resistor.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
A device used to store electrical energy.
Transformers.

27. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
5:1
100 turns.

28. A control power transformer...
2000 watts
3 -979 Volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Hyperventilation.

29. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
Lower current and higher voltage
75 turns.
Reverse its rotation.

30. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Short-circuited after power has been removed.
Four times less than that of the secondary.
Potential transformer.
Continuous.

31. Three-phase AC underground cables must be provided with overcurrent protection using a...
Because less current flowing at high voltage causes less line loss per kilowatt.
15 feet off the ground.
Circuit Breaker.
Squirrel-cage induction motor.

32. The size of a transformer is measured in...
At least two phases
Kilovolt ampere (KVA).
Disconnect the frame-grounding conductor.
Squirrel-cage rotor.

33. AC voltage is raised or lowered by means of...
Hyperventilation.
Continuous.
Clamp-on ammeter.
Transformers.

34. At what rate should mouth-to-mouth resuscitation be applied?
Carotid pulse - which is located in the neck next to the Adam's apple.
12 to 15 times a minute.
Shunted and taped
Larger than that found in the primary winding.

35. 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.
Carotid pulse - which is located in the neck next to the Adam's apple.
It provides good speed control.
5:1
Cut around clothing that has adhered to the burned area.

36. What should the duty rating of a grounding resistor be?
800 volts.
A.C.
Hyperventilation.
Continuous.

37. 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...
Draw less current.
Tied together
Squirrel-cage induction motor.
5:1.

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

39. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
3 -979 Volts.
Short-circuited after power has been removed.
An electromagnet.

40. 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?
Squirrel-cage rotor.
3 -979 Volts.
It provides good speed control.
Alternating current.

41. 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?
150 turns.
They should be made by the same manufacturer.
Allow for metering voltage and Current.
It provides good speed control.

42. The primary leads of a single-phase transformer should be connected to the...
Stator windings.
Clamp-on ammeter.
Shunted and taped
H terminals.

43. Define alternating current...
15 feet off the ground.
Current changing constantly in magnitude and periodically in direction.
Because less current flowing at high voltage causes less line loss per kilowatt.
Hyperventilation.

44. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Squirrel-cage induction motor.
No.6 AWG.
Allow for metering voltage and Current.
Check to make sure that the victim is not still in contact with the electricity.

45. A solenoid coil is...
60 cycles per second (60 Hertz).
1 amp.
An electromagnet.
100 volts.

46. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
A step-up transformer.
Larger than that found in the primary winding.
2000 watts
75 turns.

47. The property of an electric circuit that opposes any change in current is called...
Tied together
At least two phases
Inductance.
They should be made by the same manufacturer.

48. The standard frequency of alternating current used at a mine is...
Derive a neutral for grounding purposes.
Second-degree burn.
Nearly constant.
60 Hertz

49. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
12 to 15 times a minute.
The chest should rise or inflate.
Current changing constantly in magnitude and periodically in direction.
15 feet off the ground.

50. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
60 cycles per second (60 Hertz).
75 turns.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.