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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. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Continuous.
Second-degree burn.
X.

2. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Squirrel-cage rotor.
15 feet off the ground.
Tied together
5:1

3. 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?
Current that changes constantly in magnitude and periodically in direction.
800 volts.
It provides good speed control.
277 volts.

4. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Disconnect the frame-grounding conductor.
1 amp.
A step-up transformer.
480 volts.

5. Current transformers - or CT's - are used to...
Larger than that found in the primary winding.
75 turns.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
25 feet.

6. When not connected to a load - the secondary leads of a current transformer should be...
An electromagnet.
At least two phases
Check to make sure that the victim is not still in contact with the electricity.
Shunted and taped

7. Define alternating current...
Transformers.
Current changing constantly in magnitude and periodically in direction.
Squirrel-cage rotor.
It provides good speed control.

8. The speed of an alternating current - squirrel-cage induction motor is...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Nearly constant.
Transformers.
2000 watts

9. 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.
5:1
A device used to store electrical energy.
Second-degree burn.
5:1.

10. Current that changes periodically in direction is...
Tied together
No.6 AWG.
25 feet.
Alternating current.

11. If any two-phase wires are reversed on a three-phase motor - the motor will...
Circuit Breaker.
Four times less than that of the secondary.
Reverse its rotation.
100 volts.

12. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Allow for metering voltage and Current.
It provides good speed control.
An electromagnet.

13. Not true about AC power?
Squirrel-cage induction motor.
It provides good speed control.
Circuit Breaker.
An electrical shock hazard may exist.

14. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Allow for metering voltage and Current.
Kilovolt ampere (KVA).
25 feet.
No.6 AWG.

15. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
Kilovolt ampere (KVA).
2000 watts
3 -979 Volts.

16. 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.
Reverse any two-phase leads.
Inductance.
60 cycles per second (60 Hertz).

17. To protect against over-current in a three-phase circuit over-current protection must be provided for...
3 -979 Volts.
The chest should rise or inflate.
At least two phases
200 volts AC.

18. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
100 volts.
480 volts.
A step-up transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

19. The primary leads of a single-phase transformer should be connected to the...
Capacitance.
Lower current and higher voltage
Four times less than that of the secondary.
H terminals.

20. 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.
5:1.
Short-circuited after power has been removed.
At least two phases
A.C.

21. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Electro-magnetism for their operation.
480 volts.
200 volts AC.
Current that changes constantly in magnitude and periodically in direction.

22. Compared to the secondary of a loaded - step-down transformer - the primary has...
60 cycles per second (60 Hertz).
Full-load - three-phase voltage.
Lower current and higher voltage.
Clamp-on ammeter.

23. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Tied together
A step-up transformer.
Isolation transformer.
Grounded phase and ground fault devices were not operating.

24. Three-phase AC underground cables must be provided with overcurrent protection using a...
Transformers.
Inductance.
Tied together
Circuit Breaker.

25. What type of 3-phase AC motor is used most often around a mine?
X.
2000 watts
600 volts.
Squirrel-cage induction motor.

26. A solenoid coil is...
An electromagnet.
Draw less current.
At the source transformer.
25 feet.

27. What is a capacitor?
2000 watts
Squirrel-cage induction motor.
100 turns.
A device used to store electrical energy.

28. Where should grounding resistors be located?
The sum of the two capacitors.
Potential transformer.
At the source transformer.
It provides good speed control.

29. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
Lower current and higher voltage
Draw less current.
Alternating current.

30. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Inductance.
Reverse any two-phase leads.
Capacitance.
They should be made by the same manufacturer.

31. What is the first step to be followed in aiding a victim of electrical shock?
Cut around clothing that has adhered to the burned area.
75 turns.
12 to 15 times a minute.
Check to make sure that the victim is not still in contact with the electricity.

32. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Zero amps.
Current changing constantly in magnitude and periodically in direction.
The chest should rise or inflate.
A step-up transformer.

33. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Inductance.
15 feet off the ground.
1 amp.

34. A transformer with a 1:1 ratio is usually a (an)...
277 volts.
Isolation transformer.
Disconnect the frame-grounding conductor.
Draw less current.

35. 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?
Isolation transformer.
100 turns.
Transformer
Reverse any two-phase leads.

36. What steps up or steps down AC voltage?
Transformer
Four times less than that of the secondary.
A.C.
60 Hertz

37. 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?
3 -979 Volts.
An electrical shock hazard may exist.
Draw less current.
Circuit Breaker.

38. The main function of CT's and PT's on a main substation is to...
Reverse its rotation.
Allow for metering voltage and Current.
Nearly constant.
Provides single-phase power to smaller loads such as lights - heaters - etc.

39. Not a symptom of electrical shock?.
Hyperventilation.
75 turns.
Four times less than that of the secondary.
The motor rotation is reversed.

40. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Squirrel-cage rotor.
At the source transformer.
Zero amps.
5:1

41. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Grounded phase and ground fault devices were not operating.
Alternating current.
75 turns.
The motor rotation is reversed.

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...
277 volts.
Allow for metering voltage and Current.
Shunted and taped
Tied together

43. Alternating current may be defined as...
60 cycles per second (60 Hertz).
Transformer
Alternating current.
Current that changes constantly in magnitude and periodically in direction.

44. A wound-rotor induction motor has all the following EXCEPT...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Lower current and higher voltage.
Squirrel-cage rotor.
Transformers.

45. 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...
60 cycles per second (60 Hertz).
No.6 AWG.
Draw less current.
A device used to store electrical energy.

46. Operating coils - motors - transformers - relays and solenoids depend upon...
60 cycles per second (60 Hertz).
The current will read zero.
Reverse its rotation.
Electro-magnetism for their operation.

47. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
Isolation transformer.
An electrical shock hazard may exist.
100 turns.

48. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
100 turns.
Electro-magnetism for their operation.
75 turns.

49. What is the danger when working around capacitors?
Inductance.
Cut around clothing that has adhered to the burned area.
1 amp.
An electrical shock hazard may exist.

50. Which of the following does a squirrel cage induction motor have?
The capacitors should be discharged.
Alternating current.
Isolation transformer.
Stator windings.