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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 transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Electro-magnetism for their operation.
25 feet.
Carotid pulse - which is located in the neck next to the Adam's apple.
A step-up transformer.

2. What is the danger when working around capacitors?
Provides single-phase power to smaller loads such as lights - heaters - etc.
An electrical shock hazard may exist.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Zero amps.

3. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
H terminals.
No.6 AWG.
Reverse its rotation.

4. Not an acceptable method for the installations of surface transformers?
H terminals.
Transformers.
They must be installed at least 7 feet above the ground.
Stator windings.

5. The primary function of a power transformer is to provide...
Because less current flowing at high voltage causes less line loss per kilowatt.
Current that changes constantly in magnitude and periodically in direction.
75 turns.
Full-load - three-phase voltage.

6. Compared to the secondary of a loaded - step-down transformer - the primary has...
At the source transformer.
Carotid pulse - which is located in the neck next to the Adam's apple.
Lower current and higher voltage.
Isolation transformer.

7. Not a symptom of electrical shock?.
Hyperventilation.
Derive a neutral for grounding purposes.
Inductance.
Reverse its rotation.

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

9. The property of an electrical circuit that opposes any change in voltage is called...
H terminals.
Reverse its rotation.
Capacitance.
600 volts.

10. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Kilovolt ampere (KVA).
480 volts.
Electro-magnetism for their operation.
7 -630 volts.

11. What steps up or steps down AC voltage?
3 -979 Volts.
5:1
A device used to store electrical energy.
Transformer

12. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Transformers.
Grounded phase and ground fault devices were not operating.
100 volts.
15 feet off the ground.

13. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
The sum of the two capacitors.
A step-up transformer.
No.6 AWG.
100 volts.

14. The size of a transformer is measured in...
Full-load - three-phase voltage.
277 volts.
Kilovolt ampere (KVA).
Squirrel-cage induction motor.

15. How do you change the direction of a 3-phase AC motor?
75 turns.
An electromagnet.
A.C.
Reverse any two-phase leads.

16. 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...
Second-degree burn.
Draw less current.
480 volts.
Stator windings.

17. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
A device used to store electrical energy.
25 feet.
277 volts.
Transformers.

18. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Capacitance.
Current changing constantly in magnitude and periodically in direction.
The motor rotation is reversed.
X.

19. 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...
At least two phases
Transformer
Short-circuited after power has been removed.
Draw less current.

20. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Kilovolt ampere (KVA).
The chest should rise or inflate.
A step-up transformer.
They must be installed at least 7 feet above the ground.

21. 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?
A device used to store electrical energy.
100 volts.
75 turns.
7 -630 volts.

22. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
They should be made by the same manufacturer.
An electrical shock hazard may exist.
Short-circuited after power has been removed.
Draw less current.

23. The combined capacitance of two capacitors in parallel is...
Short-circuited after power has been removed.
The capacitors should be discharged.
The sum of the two capacitors.
Zero amps.

24. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
It provides good speed control.
Tied together
Transformers.

25. The main function of CT's and PT's on a main substation is to...
600 volts.
75 turns.
Allow for metering voltage and Current.
Reverse any two-phase leads.

26. 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.
A device used to store electrical energy.
5:1
Kilovolt ampere (KVA).
Draw less current.

27. 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...
Tied together
A grounding resistor.
25 feet.
Two speeds

28. Current transformers - or CT's - are used to...
60 Hertz
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Larger than that found in the primary winding.
Potential transformer.

29. What type motor is a wound-rotor induction motor?
A.C.
Inductance.
15 feet off the ground.
X.

30. 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.
100 volts.
Cut around clothing that has adhered to the burned area.
277 volts.

31. At what rate should mouth-to-mouth resuscitation be applied?
Squirrel-cage rotor.
A.C.
Two speeds
12 to 15 times a minute.

32. Operating coils - motors - transformers - relays and solenoids depend upon...
Stator windings.
Electro-magnetism for their operation.
A grounding resistor.
Lower current and higher voltage

33. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Tied together
200 volts AC.
7 -630 volts.
Capacitance.

34. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
75 turns.
Circuit Breaker.
3 -979 Volts.
The current will read zero.

35. The standard frequency of alternating current used at a mine is...
Current changing constantly in magnitude and periodically in direction.
15 feet off the ground.
60 Hertz
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

36. 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?
Inductance.
3 -979 Volts.
Reverse any two-phase leads.
Squirrel-cage rotor.

37. The primary leads of a single-phase transformer should be connected to the...
Four times less than that of the secondary.
600 volts.
H terminals.
Second-degree burn.

38. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
2000 watts
Second-degree burn.
Transformer
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

39. What type of 3-phase AC motor is used most often around a mine?
Short-circuited after power has been removed.
They must be installed at least 7 feet above the ground.
Squirrel-cage induction motor.
15 feet off the ground.

40. 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 cycles per second (60 Hertz).
25 feet.
3 -979 Volts.

41. 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?
150 turns.
Two speeds
60 Hertz
A.C.

42. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Carotid pulse - which is located in the neck next to the Adam's apple.
The motor rotation is reversed.
Larger than that found in the primary winding.
Current that changes constantly in magnitude and periodically in direction.

43. 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 motor rotation is reversed.
3 -979 Volts.
Carotid pulse - which is located in the neck next to the Adam's apple.

44. Compared to the secondary of a loaded - step-down transformer - the primary has...
3 -979 Volts.
Lower current and higher voltage
A.C.
Clamp-on ammeter.

45. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Tied together
Zero amps.
Inductance.
600 volts.

46. A solenoid coil is...
An electromagnet.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
5:1
100 volts.

47. A transformer with a 1:1 ratio is usually a (an)...
At least two phases
Larger than that found in the primary winding.
The chest should rise or inflate.
Isolation transformer.

48. AC voltage is raised or lowered by means of...
Electro-magnetism for their operation.
Transformers.
The chest should rise or inflate.
Circuit Breaker.

49. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
Transformers.
It provides good speed control.
Full-load - three-phase voltage.

50. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
7 -630 volts.
Inductance.
2000 watts
It provides good speed control.