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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. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
They must be installed at least 7 feet above the ground.
Current that changes constantly in magnitude and periodically in direction.
Kilovolt ampere (KVA).

2. When not connected to a load - the secondary leads of a current transformer should be...
Disconnect the frame-grounding conductor.
Shunted and taped
3 -979 Volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

3. 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.
12 to 15 times a minute.
Because less current flowing at high voltage causes less line loss per kilowatt.
Potential transformer.

4. 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?
Disconnect the frame-grounding conductor.
200 volts AC.
Because less current flowing at high voltage causes less line loss per kilowatt.
Nearly constant.

5. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Clamp-on ammeter.
Check to make sure that the victim is not still in contact with the electricity.
Lower current and higher voltage.

6. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Zero amps.
A step-up transformer.
Current that changes constantly in magnitude and periodically in direction.
5:1

7. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Lower current and higher voltage
The current will read zero.
Alternating current.
Electro-magnetism for their operation.

8. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
2000 watts
Shunted and taped
Current that changes constantly in magnitude and periodically in direction.
277 volts.

9. 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?
Capacitance.
No.6 AWG.
Circuit Breaker.
75 turns.

10. 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.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
5:1.
Capacitance.
7 -630 volts.

11. The combined capacitance of two capacitors in parallel is...
Grounded phase and ground fault devices were not operating.
Inductance.
The sum of the two capacitors.
Nearly constant.

12. 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.
15 feet off the ground.
They must be installed at least 7 feet above the ground.
200 volts AC.

13. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Kilovolt ampere (KVA).
12 to 15 times a minute.
Four times less than that of the secondary.

14. Compared to the secondary of a loaded - step-down transformer - the primary has...
Reverse any two-phase leads.
Lower current and higher voltage
X.
Derive a neutral for grounding purposes.

15. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
They must be installed at least 7 feet above the ground.
3 -979 Volts.
7 -630 volts.
Kilovolt ampere (KVA).

16. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
Current changing constantly in magnitude and periodically in direction.
Hyperventilation.
Lower current and higher voltage

17. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
2000 watts
Because less current flowing at high voltage causes less line loss per kilowatt.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

18. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Stator windings.
Transformers.
25 feet.

19. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
800 volts.
100 turns.
The motor rotation is reversed.
Shunted and taped

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

21. What should the duty rating of a grounding resistor be?
Isolation transformer.
Continuous.
600 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

22. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
Second-degree burn.
Transformers.
Circuit Breaker.

23. A burn causing a blister is classified as a...
Draw less current.
A step-up transformer.
Potential transformer.
Second-degree burn.

24. 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...
100 volts.
Second-degree burn.
Full-load - three-phase voltage.
Carotid pulse - which is located in the neck next to the Adam's apple.

25. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
At least two phases
An electrical shock hazard may exist.
25 feet.
150 turns.

26. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A grounding resistor.
800 volts.
Nearly constant.
1 amp.

27. Not true about AC power?
Second-degree burn.
Shunted and taped
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
It provides good speed control.

28. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
At the source transformer.
Grounded phase and ground fault devices were not operating.
75 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.

29. Not an acceptable method for the installations of surface transformers?
7 -630 volts.
They must be installed at least 7 feet above the ground.
277 volts.
Short-circuited after power has been removed.

30. Current transformers - or CT's - are used to...
5:1.
It provides good speed control.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The chest should rise or inflate.

31. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
A device used to store electrical energy.
800 volts.
2000 watts
A.C.

32. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
Clamp-on ammeter.
200 volts AC.
An electrical shock hazard may exist.

33. Not a symptom of electrical shock?.
Kilovolt ampere (KVA).
Because less current flowing at high voltage causes less line loss per kilowatt.
Hyperventilation.
An electromagnet.

34. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Draw less current.
A.C.
Two speeds

35. Current in an AC circuit may be measured by...
Cut around clothing that has adhered to the burned area.
They must be installed at least 7 feet above the ground.
Clamp-on ammeter.
1 amp.

36. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
800 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Clamp-on ammeter.

37. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Full-load - three-phase voltage.
Draw less current.
480 volts.
A grounding resistor.

38. 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?
200 volts AC.
75 turns.
At least two phases
600 volts.

39. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
3 -979 Volts.
Stator windings.
The current will read zero.

40. 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?
Tied together
150 turns.
5:1
60 Hertz

41. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
600 volts.
12 to 15 times a minute.
Reverse its rotation.

42. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Tied together
15 feet off the ground.
Circuit Breaker.
The chest should rise or inflate.

43. The transformer used only to measure voltage is a...
Shunted and taped
Grounded phase and ground fault devices were not operating.
Potential transformer.
12 to 15 times a minute.

44. If any two-phase wires are reversed on a three-phase motor - the motor will...
Larger than that found in the primary winding.
Lower current and higher voltage.
They should be made by the same manufacturer.
Reverse its rotation.

45. The main function of CT's and PT's on a main substation is to...
Because less current flowing at high voltage causes less line loss per kilowatt.
Check to make sure that the victim is not still in contact with the electricity.
Inductance.
Allow for metering voltage and Current.

46. What is a capacitor?
Full-load - three-phase voltage.
A device used to store electrical energy.
Reverse any two-phase leads.
Disconnect the frame-grounding conductor.

47. What is the first step to be followed in aiding a victim of electrical shock?
Check to make sure that the victim is not still in contact with the electricity.
15 feet off the ground.
The capacitors should be discharged.
2000 watts

48. What is the danger when working around capacitors?
Cut around clothing that has adhered to the burned area.
Current that changes constantly in magnitude and periodically in direction.
An electrical shock hazard may exist.
7 -630 volts.

49. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
The chest should rise or inflate.
Stator windings.
100 turns.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

50. The purpose of a zig-zag transformer is to...
X.
Circuit Breaker.
Derive a neutral for grounding purposes.
Hyperventilation.