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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. 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...
The sum of the two capacitors.
Squirrel-cage induction motor.
The motor rotation is reversed.
100 volts.

2. Current that changes periodically in direction is...
Draw less current.
100 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
Alternating current.

3. 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?
Larger than that found in the primary winding.
100 turns.
5:1.
The motor rotation is reversed.

4. The property of an electric circuit that opposes any change in current is called...
Inductance.
7 -630 volts.
The current will read zero.
100 volts.

5. 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?
75 turns.
1 amp.
480 volts.
Stator windings.

6. The main function of CT's and PT's on a main substation is to...
Draw less current.
An electrical shock hazard may exist.
The current will read zero.
Allow for metering voltage and Current.

7. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
2000 watts
Isolation transformer.
X.

8. The size of a transformer is measured in...
480 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
Kilovolt ampere (KVA).
Electro-magnetism for their operation.

9. How should clothing be removed from a burn?
They must be installed at least 7 feet above the ground.
Cut around clothing that has adhered to the burned area.
It provides good speed control.
Current changing constantly in magnitude and periodically in direction.

10. What is a capacitor?
A device used to store electrical energy.
An electromagnet.
At the source transformer.
Four times less than that of the secondary.

11. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
60 Hertz
Zero amps.
Current changing constantly in magnitude and periodically in direction.
Carotid pulse - which is located in the neck next to the Adam's apple.

12. The speed of an alternating current - squirrel-cage induction motor is...
Grounded phase and ground fault devices were not operating.
Full-load - three-phase voltage.
Nearly constant.
277 volts.

13. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
A device used to store electrical energy.
15 feet off the ground.
The capacitors should be discharged.

14. At what rate should mouth-to-mouth resuscitation be applied?
The capacitors should be discharged.
12 to 15 times a minute.
The chest should rise or inflate.
Circuit Breaker.

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?
75 turns.
60 Hertz
3 -979 Volts.
150 turns.

16. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Check to make sure that the victim is not still in contact with the electricity.
Current changing constantly in magnitude and periodically in direction.
1 amp.
480 volts.

17. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
A.C.
Stator windings.
The chest should rise or inflate.
Carotid pulse - which is located in the neck next to the Adam's apple.

18. What steps up or steps down AC voltage?
The chest should rise or inflate.
7 -630 volts.
Transformer
Hyperventilation.

19. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
5:1.
Short-circuited after power has been removed.
Provides single-phase power to smaller loads such as lights - heaters - etc.
No.6 AWG.

20. The transformer used only to measure voltage is a...
Potential transformer.
Electro-magnetism for their operation.
Current changing constantly in magnitude and periodically in direction.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

21. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
15 feet off the ground.
Electro-magnetism for their operation.
At least two phases

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?
200 volts AC.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Shunted and taped
No.6 AWG.

23. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Larger than that found in the primary winding.
They must be installed at least 7 feet above the ground.
Two speeds
3 -979 Volts.

24. Which of the following does a squirrel cage induction motor have?
Stator windings.
At the source transformer.
Derive a neutral for grounding purposes.
1 amp.

25. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Draw less current.
277 volts.
Potential transformer.

26. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
At least two phases
Transformers.

27. Not a symptom of electrical shock?.
15 feet off the ground.
Draw less current.
Capacitance.
Hyperventilation.

28. 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.
Tied together
At least two phases
5:1.
Reverse its rotation.

29. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Carotid pulse - which is located in the neck next to the Adam's apple.
60 Hertz
No.6 AWG.
100 turns.

30. 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.
An electrical shock hazard may exist.
Potential transformer.
5:1
12 to 15 times a minute.

31. What is the danger when working around capacitors?
At least two phases
An electrical shock hazard may exist.
100 turns.
600 volts.

32. A solenoid coil is...
5:1
An electromagnet.
277 volts.
2000 watts

33. All transformers step voltage up or down by...
Disconnect the frame-grounding conductor.
Tied together
Inductance.
Reverse its rotation.

34. The standard frequency of alternating current used at a mine is...
60 Hertz
Provides single-phase power to smaller loads such as lights - heaters - etc.
An electromagnet.
Inductance.

35. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
The chest should rise or inflate.
150 turns.
Lower current and higher voltage

36. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Grounded phase and ground fault devices were not operating.
100 volts.
The current will read zero.
Larger than that found in the primary winding.

37. AC voltage is raised or lowered by means of...
Kilovolt ampere (KVA).
Transformers.
200 volts AC.
Zero amps.

38. 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.
60 Hertz
Clamp-on ammeter.
Reverse any two-phase leads.

39. 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?
1 amp.
600 volts.
The current will read zero.
Two speeds

40. Not true about AC power?
X.
480 volts.
It provides good speed control.
12 to 15 times a minute.

41. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Continuous.
Alternating current.
Squirrel-cage induction motor.

42. 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...
Kilovolt ampere (KVA).
Current that changes constantly in magnitude and periodically in direction.
Second-degree burn.
Tied together

43. Current transformers - or CT's - are used to...
Lower current and higher voltage.
1 amp.
Current changing constantly in magnitude and periodically in direction.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

44. A wound-rotor induction motor has all the following EXCEPT...
800 volts.
600 volts.
Squirrel-cage rotor.
277 volts.

45. How do you change the direction of a 3-phase AC motor?
Two speeds
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Nearly constant.
Reverse any two-phase leads.

46. 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...
7 -630 volts.
Draw less current.
An electromagnet.
No.6 AWG.

47. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Shunted and taped
Grounded phase and ground fault devices were not operating.
The current will read zero.

48. The standard frequency of power supplied by the power company is...
Inductance.
480 volts.
60 cycles per second (60 Hertz).
Clamp-on ammeter.

49. Compared to the secondary of a loaded - step-down transformer - the primary has...
Shunted and taped
Lower current and higher voltage.
Transformer
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

50. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
The sum of the two capacitors.
15 feet off the ground.
A grounding resistor.