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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. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
100 volts.
Four times less than that of the secondary.
Grounded phase and ground fault devices were not operating.
12 to 15 times a minute.

2. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Carotid pulse - which is located in the neck next to the Adam's apple.
Reverse any two-phase leads.
60 Hertz
No.6 AWG.

3. The standard frequency of alternating current used at a mine is...
5:1.
Allow for metering voltage and Current.
60 Hertz
Transformer

4. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Capacitance.
Four times less than that of the secondary.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Inductance.

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

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6. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
60 Hertz
Disconnect the frame-grounding conductor.
15 feet off the ground.
600 volts.

7. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Disconnect the frame-grounding conductor.
H terminals.
They should be made by the same manufacturer.
A grounding resistor.

8. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Squirrel-cage induction motor.
Clamp-on ammeter.
The motor rotation is reversed.
Draw less current.

9. The main function of CT's and PT's on a main substation is to...
At least two phases
The motor rotation is reversed.
100 turns.
Allow for metering voltage and Current.

10. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
The motor rotation is reversed.
H terminals.
3 -979 Volts.
Short-circuited after power has been removed.

11. 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
200 volts AC.
Two speeds
Draw less current.

12. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
75 turns.
3 -979 Volts.
1 amp.
Short-circuited after power has been removed.

13. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
No.6 AWG.
Stator windings.
Carotid pulse - which is located in the neck next to the Adam's apple.

14. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
X.
200 volts AC.
The chest should rise or inflate.

15. The size of a transformer is measured in...
Kilovolt ampere (KVA).
100 volts.
At the source transformer.
At least two phases

16. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
Draw less current.
Kilovolt ampere (KVA).
A.C.

17. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
150 turns.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
480 volts.
Transformers.

18. 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.
Electro-magnetism for their operation.
Reverse any two-phase leads.
The sum of the two capacitors.
5:1.

19. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
A device used to store electrical energy.
Hyperventilation.
The sum of the two capacitors.

20. What is the danger when working around capacitors?
Lower current and higher voltage
Stator windings.
An electrical shock hazard may exist.
The sum of the two capacitors.

21. Not a symptom of electrical shock?.
Clamp-on ammeter.
15 feet off the ground.
Hyperventilation.
5:1

22. Not true about AC power?
It provides good speed control.
Lower current and higher voltage.
At the source transformer.
Alternating current.

23. What is the first step to be followed in aiding a victim of electrical shock?
At the source transformer.
Full-load - three-phase voltage.
An electrical shock hazard may exist.
Check to make sure that the victim is not still in contact with the electricity.

24. If any two-phase wires are reversed on a three-phase motor - the motor will...
Current changing constantly in magnitude and periodically in direction.
Lower current and higher voltage.
Reverse its rotation.
Electro-magnetism for their operation.

25. The combined capacitance of two capacitors in parallel is...
Isolation transformer.
Four times less than that of the secondary.
Carotid pulse - which is located in the neck next to the Adam's apple.
The sum of the two capacitors.

26. A transformer has a primary voltage of 2 -800 volts and a secondary reading of 140 volts. If there are 2000 turns on the primary - how many turns are on the secondary?
The sum of the two capacitors.
100 turns.
7 -630 volts.
The current will read zero.

27. The speed of an alternating current - squirrel-cage induction motor is...
2000 watts
At least two phases
Nearly constant.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

28. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Potential transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
100 volts.

29. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
60 Hertz
A step-up transformer.
H terminals.
150 turns.

30. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Full-load - three-phase voltage.
600 volts.
At least two phases
Four times less than that of the secondary.

31. The transformer used only to measure voltage is a...
Lower current and higher voltage
Inductance.
2000 watts
Potential transformer.

32. Not an acceptable method for the installations of surface transformers?
Draw less current.
Tied together
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
They must be installed at least 7 feet above the ground.

33. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
An electromagnet.
A grounding resistor.
At least two phases
Cut around clothing that has adhered to the burned area.

34. Alternating current may be defined as...
The chest should rise or inflate.
200 volts AC.
Draw less current.
Current that changes constantly in magnitude and periodically in direction.

35. The purpose of a zig-zag transformer is to...
The motor rotation is reversed.
Draw less current.
Cut around clothing that has adhered to the burned area.
Derive a neutral for grounding purposes.

36. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
277 volts.
The motor rotation is reversed.
75 turns.
Allow for metering voltage and Current.

37. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
75 turns.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Current changing constantly in magnitude and periodically in direction.

38. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Squirrel-cage induction motor.
Inductance.
7 -630 volts.
A device used to store electrical energy.

39. Where should grounding resistors be located?
480 volts.
Derive a neutral for grounding purposes.
Inductance.
At the source transformer.

40. Operating coils - motors - transformers - relays and solenoids depend upon...
Second-degree burn.
H terminals.
Electro-magnetism for their operation.
A grounding resistor.

41. A solenoid coil is...
100 turns.
7 -630 volts.
H terminals.
An electromagnet.

42. The primary leads of a single-phase transformer should be connected to the...
Squirrel-cage rotor.
Continuous.
H terminals.
100 turns.

43. 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?
3 -979 Volts.
No.6 AWG.
75 turns.
800 volts.

44. A transformer with a 1:1 ratio is usually a (an)...
The sum of the two capacitors.
12 to 15 times a minute.
Isolation transformer.
Stator windings.

45. All transformers step voltage up or down by...
Continuous.
Reverse any two-phase leads.
75 turns.
Inductance.

46. At what rate should mouth-to-mouth resuscitation be applied?
Second-degree burn.
1 amp.
Tied together
12 to 15 times a minute.

47. Current that changes periodically in direction is...
5:1.
2000 watts
No.6 AWG.
Alternating current.

48. What steps up or steps down AC voltage?
Hyperventilation.
A step-up transformer.
The capacitors should be discharged.
Transformer

49. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Stator windings.
A device used to store electrical energy.
150 turns.

50. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
25 feet.
Circuit Breaker.
The current will read zero.
277 volts.