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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. What type of 3-phase AC motor is used most often around a mine?
Potential transformer.
Transformers.
Squirrel-cage induction motor.
They should be made by the same manufacturer.

2. AC voltage is raised or lowered by means of...
Transformers.
They should be made by the same manufacturer.
Hyperventilation.
25 feet.

3. What is the first step to be followed in aiding a victim of electrical shock?
100 turns.
Provides single-phase power to smaller loads such as lights - heaters - etc.
They must be installed at least 7 feet above the ground.
Check to make sure that the victim is not still in contact with the electricity.

4. A transformer with a 1:1 ratio is usually a (an)...
Grounded phase and ground fault devices were not operating.
12 to 15 times a minute.
Isolation transformer.
A.C.

5. Not a symptom of electrical shock?.
Hyperventilation.
15 feet off the ground.
Capacitance.
600 volts.

6. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Isolation transformer.
Larger than that found in the primary winding.
Inductance.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

7. 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.
An electromagnet.
Squirrel-cage rotor.
100 turns.

8. The transformer used only to measure voltage is a...
The sum of the two capacitors.
Nearly constant.
Potential transformer.
Inductance.

9. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Capacitance.
Isolation transformer.
At least two phases
Zero amps.

10. All transformers step voltage up or down by...
800 volts.
Inductance.
15 feet off the ground.
1 amp.

11. The speed of an alternating current - squirrel-cage induction motor is...
100 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
200 volts AC.
Nearly constant.

12. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
2000 watts
The motor rotation is reversed.
A step-up transformer.

13. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Tied together
60 Hertz
Allow for metering voltage and Current.

14. The purpose of a zig-zag transformer is to...
The sum of the two capacitors.
Derive a neutral for grounding purposes.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Larger than that found in the primary winding.

15. 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.
An electromagnet.
Allow for metering voltage and Current.

16. The primary function of a power transformer is to provide...
15 feet off the ground.
Full-load - three-phase voltage.
Kilovolt ampere (KVA).
Reverse any two-phase leads.

17. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Circuit Breaker.
Zero amps.
480 volts.

18. Operating coils - motors - transformers - relays and solenoids depend upon...
A.C.
600 volts.
Full-load - three-phase voltage.
Electro-magnetism for their operation.

19. 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?
Electro-magnetism for their operation.
150 turns.
Larger than that found in the primary winding.
Transformers.

20. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
150 turns.
Draw less current.
25 feet.

21. A wound-rotor induction motor has all the following EXCEPT...
They must be installed at least 7 feet above the ground.
5:1.
The current will read zero.
Squirrel-cage rotor.

22. What is a capacitor?
Because less current flowing at high voltage causes less line loss per kilowatt.
A device used to store electrical energy.
Circuit Breaker.
200 volts AC.

23. The secondary windings on a 10:1 step-down transformer will have a wire size...
7 -630 volts.
Larger than that found in the primary winding.
They should be made by the same manufacturer.
Zero amps.

24. The main function of CT's and PT's on a main substation is to...
Short-circuited after power has been removed.
A grounding resistor.
Allow for metering voltage and Current.
Second-degree burn.

25. 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?
Derive a neutral for grounding purposes.
Larger than that found in the primary winding.
A device used to store electrical energy.
200 volts AC.

26. Alternating current may be defined as...
Draw less current.
At least two phases
100 volts.
Current that changes constantly in magnitude and periodically in direction.

27. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
600 volts.
800 volts.
The capacitors should be discharged.
Disconnect the frame-grounding conductor.

28. The size of a transformer is measured in...
Shunted and taped
Squirrel-cage induction motor.
Kilovolt ampere (KVA).
75 turns.

29. The standard frequency of power supplied by the power company is...
Stator windings.
Transformers.
60 cycles per second (60 Hertz).
Because less current flowing at high voltage causes less line loss per kilowatt.

30. 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...
At the source transformer.
100 turns.
Draw less current.
Tied together

31. 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.
Continuous.
A.C.
5:1.
Tied together

32. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
They should be made by the same manufacturer.
The current will read zero.
Inductance.
Continuous.

33. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Cut around clothing that has adhered to the burned area.
The current will read zero.
Reverse any two-phase leads.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

34. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Stator windings.
Reverse any two-phase leads.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Short-circuited after power has been removed.

35. 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?
Two speeds
800 volts.
3 -979 Volts.
Derive a neutral for grounding purposes.

36. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Grounded phase and ground fault devices were not operating.
12 to 15 times a minute.
Electro-magnetism for their operation.
No.6 AWG.

37. The primary leads of a single-phase transformer should be connected to the...
H terminals.
25 feet.
Inductance.
Provides single-phase power to smaller loads such as lights - heaters - etc.

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

39. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
Clamp-on ammeter.
60 cycles per second (60 Hertz).
100 volts.

40. 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.
Capacitance.
100 turns.
Reverse any two-phase leads.

41. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Two speeds
Current changing constantly in magnitude and periodically in direction.
A step-up transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

42. What should the duty rating of a grounding resistor be?
Continuous.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Draw less current.
Allow for metering voltage and Current.

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.
A step-up transformer.
Circuit Breaker.
H terminals.

44. Which of the following does a squirrel cage induction motor have?
Alternating current.
Stator windings.
60 Hertz
100 volts.

45. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
2000 watts
Short-circuited after power has been removed.
Derive a neutral for grounding purposes.
The chest should rise or inflate.

46. A solenoid coil is...
They should be made by the same manufacturer.
12 to 15 times a minute.
100 volts.
An electromagnet.

47. The combined capacitance of two capacitors in parallel is...
They should be made by the same manufacturer.
Short-circuited after power has been removed.
5:1
The sum of the two capacitors.

48. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Lower current and higher voltage
Check to make sure that the victim is not still in contact with the electricity.
Full-load - three-phase voltage.

49. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Reverse its rotation.
Lower current and higher voltage
Shunted and taped
A grounding resistor.

50. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Disconnect the frame-grounding conductor.
Allow for metering voltage and Current.
X.
Continuous.