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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. 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.
Kilovolt ampere (KVA).
Squirrel-cage rotor.
5:1.
Four times less than that of the secondary.

2. The size of a transformer is measured in...
Squirrel-cage rotor.
15 feet off the ground.
A device used to store electrical energy.
Kilovolt ampere (KVA).

3. Compared to the secondary of a loaded - step-down transformer - the primary has...
25 feet.
A device used to store electrical energy.
Lower current and higher voltage.
5:1.

4. Not a symptom of electrical shock?.
The motor rotation is reversed.
The capacitors should be discharged.
Lower current and higher voltage
Hyperventilation.

5. 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...
An electrical shock hazard may exist.
Alternating current.
Draw less current.
Provides single-phase power to smaller loads such as lights - heaters - etc.

6. AC voltage is raised or lowered by means of...
Transformers.
X.
Disconnect the frame-grounding conductor.
15 feet off the ground.

7. What type motor is a wound-rotor induction motor?
A.C.
An electromagnet.
Lower current and higher voltage
Because less current flowing at high voltage causes less line loss per kilowatt.

8. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Reverse any two-phase leads.
Electro-magnetism for their operation.
Draw less current.

9. Not an acceptable method for the installations of surface transformers?
Circuit Breaker.
They must be installed at least 7 feet above the ground.
15 feet off the ground.
Stator windings.

10. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
Hyperventilation.
277 volts.
A.C.

11. 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.
Carotid pulse - which is located in the neck next to the Adam's apple.
Transformer
Lower current and higher voltage

12. What type of 3-phase AC motor is used most often around a mine?
H terminals.
X.
Shunted and taped
Squirrel-cage induction motor.

13. What steps up or steps down AC voltage?
Transformer
5:1
H terminals.
60 cycles per second (60 Hertz).

14. 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?
Reverse any two-phase leads.
The current will read zero.
15 feet off the ground.
3 -979 Volts.

15. The standard frequency of alternating current used at a mine is...
1 amp.
60 Hertz
Zero amps.
An electromagnet.

16. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Two speeds
5:1.
X.
200 volts AC.

17. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
60 cycles per second (60 Hertz).
60 Hertz
7 -630 volts.
2000 watts

18. A solenoid coil is...
An electromagnet.
Short-circuited after power has been removed.
Lower current and higher voltage
X.

19. Three-phase AC underground cables must be provided with overcurrent protection using a...
No.6 AWG.
5:1.
Circuit Breaker.
X.

20. 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...
Current that changes constantly in magnitude and periodically in direction.
200 volts AC.
Draw less current.
Larger than that found in the primary winding.

21. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Cut around clothing that has adhered to the burned area.
The capacitors should be discharged.
Capacitance.
480 volts.

22. How should clothing be removed from a burn?
Derive a neutral for grounding purposes.
At least two phases
Carotid pulse - which is located in the neck next to the Adam's apple.
Cut around clothing that has adhered to the burned area.

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

24. All transformers step voltage up or down by...
Stator windings.
Inductance.
Reverse any two-phase leads.
Two speeds

25. Which of the following does a squirrel cage induction motor have?
The motor rotation is reversed.
A device used to store electrical energy.
Stator windings.
Zero amps.

26. 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...
100 volts.
Disconnect the frame-grounding conductor.
Cut around clothing that has adhered to the burned area.
Draw less current.

27. 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.
Hyperventilation.
Because less current flowing at high voltage causes less line loss per kilowatt.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

28. Where should grounding resistors be located?
At the source transformer.
5:1.
Clamp-on ammeter.
2000 watts

29. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Inductance.
Allow for metering voltage and Current.
The motor rotation is reversed.
5:1

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

31. 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?
Reverse its rotation.
A grounding resistor.
75 turns.
Isolation transformer.

32. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Four times less than that of the secondary.
Capacitance.
15 feet off the ground.
Squirrel-cage induction motor.

33. 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?
Electro-magnetism for their operation.
150 turns.
No.6 AWG.
Allow for metering voltage and Current.

34. The speed of an alternating current - squirrel-cage induction motor is...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Full-load - three-phase voltage.
Nearly constant.
12 to 15 times a minute.

35. 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...
Current changing constantly in magnitude and periodically in direction.
Tied together
150 turns.
60 cycles per second (60 Hertz).

36. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
An electrical shock hazard may exist.
The current will read zero.
Current changing constantly in magnitude and periodically in direction.
Lower current and higher voltage

37. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
The chest should rise or inflate.
600 volts.
Stator windings.

38. 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?
600 volts.
Derive a neutral for grounding purposes.
Hyperventilation.
Current that changes constantly in magnitude and periodically in direction.

39. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
150 turns.
Two speeds
Zero amps.
Transformers.

40. 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?
Second-degree burn.
75 turns.
5:1
800 volts.

41. A control power transformer...
Grounded phase and ground fault devices were not operating.
The motor rotation is reversed.
75 turns.
Provides single-phase power to smaller loads such as lights - heaters - etc.

42. What is a capacitor?
200 volts AC.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Lower current and higher voltage.
A device used to store electrical energy.

43. A transformer with a 1:1 ratio is usually a (an)...
Short-circuited after power has been removed.
5:1.
Isolation transformer.
Check to make sure that the victim is not still in contact with the electricity.

44. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Tied together
No.6 AWG.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

45. 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.
Derive a neutral for grounding purposes.
Second-degree burn.
Allow for metering voltage and Current.

46. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Cut around clothing that has adhered to the burned area.
The chest should rise or inflate.
Derive a neutral for grounding purposes.
7 -630 volts.

47. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
An electromagnet.
Two speeds
A step-up transformer.
A grounding resistor.

48. High voltage is used to transmit power over long distances...
Capacitance.
Reverse its rotation.
Kilovolt ampere (KVA).
Because less current flowing at high voltage causes less line loss per kilowatt.

49. If any two-phase wires are reversed on a three-phase motor - the motor will...
Current changing constantly in magnitude and periodically in direction.
Reverse its rotation.
Lower current and higher voltage
150 turns.

50. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
The sum of the two capacitors.
7 -630 volts.
Allow for metering voltage and Current.