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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 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...
Squirrel-cage rotor.
At the source transformer.
800 volts.
Tied together

2. What is a capacitor?
Inductance.
Short-circuited after power has been removed.
A device used to store electrical energy.
A.C.

3. What type of 3-phase AC motor is used most often around a mine?
Second-degree burn.
150 turns.
Short-circuited after power has been removed.
Squirrel-cage induction motor.

4. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Squirrel-cage induction motor.
A.C.
The current will read zero.
Hyperventilation.

5. The purpose of a zig-zag transformer is to...
Tied together
Carotid pulse - which is located in the neck next to the Adam's apple.
Derive a neutral for grounding purposes.
Transformers.

6. The combined capacitance of two capacitors in parallel is...
Two speeds
The sum of the two capacitors.
75 turns.
Disconnect the frame-grounding conductor.

7. 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...
Nearly constant.
Draw less current.
Provides single-phase power to smaller loads such as lights - heaters - etc.
At the source transformer.

8. 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?
Isolation transformer.
They must be installed at least 7 feet above the ground.
H terminals.
800 volts.

9. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Potential transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Alternating current.

10. 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.
Reverse any two-phase leads.
5:1
Larger than that found in the primary winding.
Short-circuited after power has been removed.

11. What steps up or steps down AC voltage?
Alternating current.
No.6 AWG.
At least two phases
Transformer

12. What type motor is a wound-rotor induction motor?
15 feet off the ground.
200 volts AC.
A device used to store electrical energy.
A.C.

13. The property of an electric circuit that opposes any change in current is called...
Provides single-phase power to smaller loads such as lights - heaters - etc.
7 -630 volts.
The current will read zero.
Inductance.

14. 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?
800 volts.
150 turns.
100 volts.
Four times less than that of the secondary.

15. 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?
The capacitors should be discharged.
Two speeds
75 turns.
An electrical shock hazard may exist.

16. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
800 volts.
Kilovolt ampere (KVA).
Two speeds

17. The speed of an alternating current - squirrel-cage induction motor is...
Carotid pulse - which is located in the neck next to the Adam's apple.
Lower current and higher voltage.
Nearly constant.
Cut around clothing that has adhered to the burned area.

18. High voltage is used to transmit power over long distances...
Hyperventilation.
Because less current flowing at high voltage causes less line loss per kilowatt.
7 -630 volts.
Zero amps.

19. How do you change the direction of a 3-phase AC motor?
Clamp-on ammeter.
Reverse any two-phase leads.
A.C.
Short-circuited after power has been removed.

20. How should clothing be removed from a burn?
800 volts.
600 volts.
Cut around clothing that has adhered to the burned area.
277 volts.

21. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
5:1.
At the source transformer.
At least two phases

22. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
It provides good speed control.
Inductance.
Potential transformer.

23. To protect against over-current in a three-phase circuit over-current protection must be provided for...
H terminals.
Cut around clothing that has adhered to the burned area.
Lower current and higher voltage.
At least two phases

24. A solenoid coil is...
Second-degree burn.
An electromagnet.
Capacitance.
Alternating current.

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

26. 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.
Current changing constantly in magnitude and periodically in direction.
75 turns.
The chest should rise or inflate.

27. 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.
The capacitors should be discharged.
150 turns.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

28. Current that changes periodically in direction is...
Two speeds
150 turns.
Alternating current.
Allow for metering voltage and Current.

29. 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.
They should be made by the same manufacturer.
12 to 15 times a minute.
Two speeds

30. What is the danger when working around capacitors?
25 feet.
5:1
An electrical shock hazard may exist.
60 cycles per second (60 Hertz).

31. At what rate should mouth-to-mouth resuscitation be applied?
H terminals.
12 to 15 times a minute.
Stator windings.
At the source transformer.

32. A control power transformer...
277 volts.
Transformer
Alternating current.
Provides single-phase power to smaller loads such as lights - heaters - etc.

33. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Current that changes constantly in magnitude and periodically in direction.
7 -630 volts.
1 amp.
Shunted and taped

34. 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?
277 volts.
Zero amps.
600 volts.
100 volts.

35. Three-phase AC underground cables must be provided with overcurrent protection using a...
100 turns.
Circuit Breaker.
Current changing constantly in magnitude and periodically in direction.
The current will read zero.

36. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
5:1
Squirrel-cage rotor.
25 feet.

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?
The motor rotation is reversed.
Hyperventilation.
3 -979 Volts.
Alternating current.

38. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
150 turns.
They should be made by the same manufacturer.
The motor rotation is reversed.
12 to 15 times a minute.

39. AC voltage is raised or lowered by means of...
Isolation transformer.
Transformers.
No.6 AWG.
Draw less current.

40. Compared to the secondary of a loaded - step-down transformer - the primary has...
Draw less current.
3 -979 Volts.
Lower current and higher voltage.
Shunted and taped

41. 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?
Full-load - three-phase voltage.
Grounded phase and ground fault devices were not operating.
200 volts AC.
Zero amps.

42. The standard frequency of power supplied by the power company is...
Larger than that found in the primary winding.
60 cycles per second (60 Hertz).
Squirrel-cage rotor.
Shunted and taped

43. All transformers step voltage up or down by...
75 turns.
Isolation transformer.
Inductance.
Squirrel-cage induction motor.

44. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Current that changes constantly in magnitude and periodically in direction.
A step-up transformer.
Four times less than that of the secondary.
No.6 AWG.

45. The standard frequency of alternating current used at a mine is...
150 turns.
60 Hertz
Two speeds
Transformers.

46. Current in an AC circuit may be measured by...
Transformer
A grounding resistor.
An electromagnet.
Clamp-on ammeter.

47. If any two-phase wires are reversed on a three-phase motor - the motor will...
Two speeds
An electromagnet.
75 turns.
Reverse its rotation.

48. The size of a transformer is measured in...
Carotid pulse - which is located in the neck next to the Adam's apple.
100 volts.
Kilovolt ampere (KVA).
3 -979 Volts.

49. Not true about AC power?
60 Hertz
It provides good speed control.
100 turns.
Shunted and taped

50. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
Because less current flowing at high voltage causes less line loss per kilowatt.
Circuit Breaker.
It provides good speed control.