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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 a 1:1 ratio is usually a (an)...
An electrical shock hazard may exist.
3 -979 Volts.
Isolation transformer.
Four times less than that of the secondary.

2. The standard frequency of alternating current used at a mine is...
60 cycles per second (60 Hertz).
60 Hertz
Derive a neutral for grounding purposes.
Draw less current.

3. The property of an electrical circuit that opposes any change in voltage is called...
150 turns.
Transformer
Capacitance.
Lower current and higher voltage

4. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
5:1.
100 volts.
They must be installed at least 7 feet above the ground.

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

6. 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.
Squirrel-cage induction motor.
The current will read zero.
The motor rotation is reversed.

7. Which of the following does a squirrel cage induction motor have?
Stator windings.
5:1
60 Hertz
75 turns.

8. What should the duty rating of a grounding resistor be?
75 turns.
A.C.
Check to make sure that the victim is not still in contact with the electricity.
Continuous.

9. A burn causing a blister is classified as a...
A device used to store electrical energy.
Tied together
Second-degree burn.
Shunted and taped

10. 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...
Draw less current.
25 feet.
5:1.
Because less current flowing at high voltage causes less line loss per kilowatt.

11. 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...
Current that changes constantly in magnitude and periodically in direction.
Tied together
The capacitors should be discharged.
Lower current and higher voltage

12. If any two-phase wires are reversed on a three-phase motor - the motor will...
An electromagnet.
12 to 15 times a minute.
Reverse its rotation.
Stator windings.

13. The primary function of a power transformer is to provide...
Capacitance.
Full-load - three-phase voltage.
Because less current flowing at high voltage causes less line loss per kilowatt.
Disconnect the frame-grounding conductor.

14. The main function of CT's and PT's on a main substation is to...
Full-load - three-phase voltage.
The chest should rise or inflate.
Allow for metering voltage and Current.
Short-circuited after power has been removed.

15. How should clothing be removed from a burn?
75 turns.
Cut around clothing that has adhered to the burned area.
The chest should rise or inflate.
Two speeds

16. What steps up or steps down AC voltage?
X.
Inductance.
Capacitance.
Transformer

17. A solenoid coil is...
15 feet off the ground.
A device used to store electrical energy.
An electromagnet.
5:1.

18. What type of 3-phase AC motor is used most often around a mine?
25 feet.
Cut around clothing that has adhered to the burned area.
Disconnect the frame-grounding conductor.
Squirrel-cage induction motor.

19. 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...
60 cycles per second (60 Hertz).
Two speeds
They should be made by the same manufacturer.
Draw less current.

20. The secondary windings on a 10:1 step-down transformer will have a wire size...
5:1
Larger than that found in the primary winding.
Derive a neutral for grounding purposes.
At least two phases

21. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
A grounding resistor.
The capacitors should be discharged.
480 volts.
No.6 AWG.

22. 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.
A device used to store electrical energy.
Lower current and higher voltage.
Squirrel-cage induction motor.
5:1.

23. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
1 amp.
They should be made by the same manufacturer.
75 turns.
A device used to store electrical energy.

24. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Lower current and higher voltage
Zero amps.
Provides single-phase power to smaller loads such as lights - heaters - etc.
60 Hertz

25. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Provides single-phase power to smaller loads such as lights - heaters - etc.
The motor rotation is reversed.
Squirrel-cage induction motor.
Alternating current.

26. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
The chest should rise or inflate.
Four times less than that of the secondary.
15 feet off the ground.
7 -630 volts.

27. Compared to the secondary of a loaded - step-down transformer - the primary has...
Zero amps.
Clamp-on ammeter.
Lower current and higher voltage
Grounded phase and ground fault devices were not operating.

28. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
Allow for metering voltage and Current.
Kilovolt ampere (KVA).
150 turns.

29. The property of an electric circuit that opposes any change in current is called...
150 turns.
Inductance.
Cut around clothing that has adhered to the burned area.
The capacitors should be discharged.

30. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Four times less than that of the secondary.
60 Hertz
A.C.
2000 watts

31. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
They should be made by the same manufacturer.
Squirrel-cage rotor.
Circuit Breaker.

32. 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.
Current that changes constantly in magnitude and periodically in direction.
The chest should rise or inflate.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
5:1

33. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
The chest should rise or inflate.
The current will read zero.
X.
A grounding resistor.

34. 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.
Kilovolt ampere (KVA).
The motor rotation is reversed.
Provides single-phase power to smaller loads such as lights - heaters - etc.

35. AC voltage is raised or lowered by means of...
Zero amps.
Lower current and higher voltage
Transformers.
Because less current flowing at high voltage causes less line loss per kilowatt.

36. 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?
800 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Potential transformer.
Disconnect the frame-grounding conductor.

37. What type motor is a wound-rotor induction motor?
Transformer
Because less current flowing at high voltage causes less line loss per kilowatt.
A.C.
Full-load - three-phase voltage.

38. All transformers step voltage up or down by...
Potential transformer.
Inductance.
7 -630 volts.
15 feet off the ground.

39. What is a capacitor?
277 volts.
Second-degree burn.
A device used to store electrical energy.
25 feet.

40. Not an acceptable method for the installations of surface transformers?
At least two phases
2000 watts
They must be installed at least 7 feet above the ground.
An electrical shock hazard may exist.

41. Current in an AC circuit may be measured by...
Draw less current.
Allow for metering voltage and Current.
Disconnect the frame-grounding conductor.
Clamp-on ammeter.

42. The purpose of a zig-zag transformer is to...
Larger than that found in the primary winding.
Clamp-on ammeter.
Derive a neutral for grounding purposes.
Second-degree burn.

43. What is the danger when working around capacitors?
Derive a neutral for grounding purposes.
Transformers.
An electrical shock hazard may exist.
277 volts.

44. Where should grounding resistors be located?
At the source transformer.
Squirrel-cage rotor.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
200 volts AC.

45. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Inductance.
Lower current and higher voltage
Hyperventilation.
The chest should rise or inflate.

46. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Tied together
They should be made by the same manufacturer.
Draw less current.

47. Current transformers - or CT's - are used to...
Grounded phase and ground fault devices were not operating.
Carotid pulse - which is located in the neck next to the Adam's apple.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Current changing constantly in magnitude and periodically in direction.

48. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
An electrical shock hazard may exist.
Transformer
60 cycles per second (60 Hertz).

49. 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...
Second-degree burn.
100 volts.
Electro-magnetism for their operation.
60 cycles per second (60 Hertz).

50. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
480 volts.
A.C.
Short-circuited after power has been removed.
The current will read zero.