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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...
Check to make sure that the victim is not still in contact with the electricity.
Tied together
Reverse its rotation.
Allow for metering voltage and Current.

2. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
7 -630 volts.
The current will read zero.
H terminals.
800 volts.

3. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
At the source transformer.
Short-circuited after power has been removed.
Transformers.

4. Current that changes periodically in direction is...
Alternating current.
1 amp.
Four times less than that of the secondary.
Lower current and higher voltage.

5. A control power transformer...
Circuit Breaker.
15 feet off the ground.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Stator windings.

6. 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.
Allow for metering voltage and Current.
5:1.
75 turns.
2000 watts

7. AC voltage is raised or lowered by means of...
An electromagnet.
2000 watts
25 feet.
Transformers.

8. A solenoid coil is...
Clamp-on ammeter.
Check to make sure that the victim is not still in contact with the electricity.
Disconnect the frame-grounding conductor.
An electromagnet.

9. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
Check to make sure that the victim is not still in contact with the electricity.
Reverse its rotation.
100 volts.

10. The purpose of a zig-zag transformer is to...
Clamp-on ammeter.
Check to make sure that the victim is not still in contact with the electricity.
At the source transformer.
Derive a neutral for grounding purposes.

11. A wound-rotor induction motor has all the following EXCEPT...
75 turns.
Squirrel-cage induction motor.
480 volts.
Squirrel-cage rotor.

12. 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...
A step-up transformer.
75 turns.
The sum of the two capacitors.
100 volts.

13. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Larger than that found in the primary winding.
Short-circuited after power has been removed.
Circuit Breaker.
Inductance.

14. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
2000 watts
An electromagnet.
100 volts.
800 volts.

15. The transformer used only to measure voltage is a...
Potential transformer.
The current will read zero.
3 -979 Volts.
Because less current flowing at high voltage causes less line loss per kilowatt.

16. When not connected to a load - the secondary leads of a current transformer should be...
Alternating current.
60 cycles per second (60 Hertz).
An electromagnet.
Shunted and taped

17. Current in an AC circuit may be measured by...
Clamp-on ammeter.
It provides good speed control.
75 turns.
Two speeds

18. The standard frequency of power supplied by the power company is...
Lower current and higher voltage.
60 cycles per second (60 Hertz).
Nearly constant.
They must be installed at least 7 feet above the ground.

19. Where should grounding resistors be located?
Potential transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
At the source transformer.
An electromagnet.

20. The secondary windings on a 10:1 step-down transformer will have a wire size...
Disconnect the frame-grounding conductor.
Short-circuited after power has been removed.
480 volts.
Larger than that found in the primary winding.

21. Not an acceptable method for the installations of surface transformers?
The capacitors should be discharged.
Two speeds
Allow for metering voltage and Current.
They must be installed at least 7 feet above the ground.

22. The property of an electrical circuit that opposes any change in voltage is called...
They must be installed at least 7 feet above the ground.
Capacitance.
The capacitors should be discharged.
Potential transformer.

23. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Electro-magnetism for their operation.
The sum of the two capacitors.
Zero amps.
75 turns.

24. At what rate should mouth-to-mouth resuscitation be applied?
75 turns.
They should be made by the same manufacturer.
12 to 15 times a minute.
7 -630 volts.

25. What is the danger when working around capacitors?
Continuous.
5:1.
An electrical shock hazard may exist.
100 turns.

26. Which of the following does a squirrel cage induction motor have?
5:1.
Stator windings.
They should be made by the same manufacturer.
100 turns.

27. The speed of an alternating current - squirrel-cage induction motor is...
Because less current flowing at high voltage causes less line loss per kilowatt.
Nearly constant.
Capacitance.
100 volts.

28. The primary leads of a single-phase transformer should be connected to the...
Electro-magnetism for their operation.
H terminals.
The sum of the two capacitors.
7 -630 volts.

29. What steps up or steps down AC voltage?
Transformer
100 turns.
Lower current and higher voltage
Shunted and taped

30. How should clothing be removed from a burn?
Nearly constant.
25 feet.
Cut around clothing that has adhered to the burned area.
Inductance.

31. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
15 feet off the ground.
Carotid pulse - which is located in the neck next to the Adam's apple.
Two speeds
No.6 AWG.

32. 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?
X.
A.C.
200 volts AC.
At the source transformer.

33. Operating coils - motors - transformers - relays and solenoids depend upon...
480 volts.
Isolation transformer.
Electro-magnetism for their operation.
The motor rotation is reversed.

34. Current transformers - or CT's - are used to...
Larger than that found in the primary winding.
Kilovolt ampere (KVA).
Nearly constant.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

35. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Tied together
It provides good speed control.
The current will read zero.
Circuit Breaker.

36. Not true about AC power?
Because less current flowing at high voltage causes less line loss per kilowatt.
Shunted and taped
Short-circuited after power has been removed.
It provides good speed control.

37. The primary function of a power transformer is to provide...
The chest should rise or inflate.
Full-load - three-phase voltage.
Reverse its rotation.
It provides good speed control.

38. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Alternating current.
At least two phases
75 turns.

39. The property of an electric circuit that opposes any change in current is called...
Isolation transformer.
Inductance.
25 feet.
Larger than that found in the primary winding.

40. What type of 3-phase AC motor is used most often around a mine?
480 volts.
Shunted and taped
100 volts.
Squirrel-cage induction motor.

41. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
277 volts.
The chest should rise or inflate.
480 volts.
Two speeds

42. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Squirrel-cage rotor.
Current changing constantly in magnitude and periodically in direction.
Draw less current.

43. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Lower current and higher voltage.
1 amp.
Cut around clothing that has adhered to the burned area.

44. 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?
15 feet off the ground.
Reverse its rotation.
75 turns.
Zero amps.

45. 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?
Shunted and taped
5:1.
75 turns.
Check to make sure that the victim is not still in contact with the electricity.

46. 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?
A grounding resistor.
150 turns.
Grounded phase and ground fault devices were not operating.
Alternating current.

47. The size of a transformer is measured in...
An electrical shock hazard may exist.
Kilovolt ampere (KVA).
Lower current and higher voltage.
Short-circuited after power has been removed.

48. Not a symptom of electrical shock?.
Current that changes constantly in magnitude and periodically in direction.
Hyperventilation.
A.C.
Because less current flowing at high voltage causes less line loss per kilowatt.

49. The standard frequency of alternating current used at a mine is...
Draw less current.
60 Hertz
Tied together
Grounded phase and ground fault devices were not operating.

50. 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?
An electromagnet.
The motor rotation is reversed.
The chest should rise or inflate.
3 -979 Volts.