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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. Alternating current may be defined as...
Derive a neutral for grounding purposes.
Current that changes constantly in magnitude and periodically in direction.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
At the source transformer.

2. Not a symptom of electrical shock?.
1 amp.
Second-degree burn.
Disconnect the frame-grounding conductor.
Hyperventilation.

3. 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.
150 turns.
No.6 AWG.
100 turns.

4. 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?
Inductance.
150 turns.
Squirrel-cage rotor.
1 amp.

5. Three-phase AC underground cables must be provided with overcurrent protection using a...
Second-degree burn.
Transformers.
Circuit Breaker.
Cut around clothing that has adhered to the burned area.

6. High voltage is used to transmit power over long distances...
An electrical shock hazard may exist.
Because less current flowing at high voltage causes less line loss per kilowatt.
Isolation transformer.
25 feet.

7. The property of an electrical circuit that opposes any change in voltage is called...
25 feet.
Capacitance.
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.

8. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Short-circuited after power has been removed.
X.
Stator windings.

9. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
75 turns.
Grounded phase and ground fault devices were not operating.
Capacitance.
Alternating current.

10. Where should grounding resistors be located?
Inductance.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
12 to 15 times a minute.
At the source transformer.

11. Compared to the secondary of a loaded - step-down transformer - the primary has...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Lower current and higher voltage.
Larger than that found in the primary winding.
Current that changes constantly in magnitude and periodically in direction.

12. At what rate should mouth-to-mouth resuscitation be applied?
Kilovolt ampere (KVA).
At the source transformer.
12 to 15 times a minute.
Squirrel-cage induction motor.

13. The secondary windings on a 10:1 step-down transformer will have a wire size...
Reverse its rotation.
Carotid pulse - which is located in the neck next to the Adam's apple.
12 to 15 times a minute.
Larger than that found in the primary winding.

14. The primary leads of a single-phase transformer should be connected to the...
H terminals.
800 volts.
Kilovolt ampere (KVA).
Disconnect the frame-grounding conductor.

15. 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?
Stator windings.
100 turns.
Full-load - three-phase voltage.
X.

16. Compared to the secondary of a loaded - step-down transformer - the primary has...
Kilovolt ampere (KVA).
No.6 AWG.
Lower current and higher voltage
Current that changes constantly in magnitude and periodically in direction.

17. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
At least two phases
No.6 AWG.
Squirrel-cage induction motor.
Isolation transformer.

18. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
15 feet off the ground.
Circuit Breaker.
No.6 AWG.

19. Not true about AC power?
It provides good speed control.
Carotid pulse - which is located in the neck next to the Adam's apple.
Reverse its rotation.
75 turns.

20. The transformer used only to measure voltage is a...
12 to 15 times a minute.
Nearly constant.
Draw less current.
Potential transformer.

21. AC voltage is raised or lowered by means of...
Transformers.
60 Hertz
Nearly constant.
The chest should rise or inflate.

22. 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.
Shunted and taped
Isolation transformer.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

23. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Reverse any two-phase leads.
H terminals.
Second-degree burn.
The motor rotation is reversed.

24. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
A grounding resistor.
They should be made by the same manufacturer.
The motor rotation is reversed.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

25. When not connected to a load - the secondary leads of a current transformer should be...
12 to 15 times a minute.
Current changing constantly in magnitude and periodically in direction.
1 amp.
Shunted and taped

26. Current that changes periodically in direction is...
Current that changes constantly in magnitude and periodically in direction.
Alternating current.
A grounding resistor.
800 volts.

27. Which of the following does a squirrel cage induction motor have?
200 volts AC.
Stator windings.
Derive a neutral for grounding purposes.
Transformers.

28. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Disconnect the frame-grounding conductor.
Provides single-phase power to smaller loads such as lights - heaters - etc.
The current will read zero.

29. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Full-load - three-phase voltage.
A grounding resistor.
Two speeds
The capacitors should be discharged.

30. The standard frequency of power supplied by the power company is...
480 volts.
Disconnect the frame-grounding conductor.
60 cycles per second (60 Hertz).
Inductance.

31. The combined capacitance of two capacitors in parallel is...
Larger than that found in the primary winding.
200 volts AC.
Hyperventilation.
The sum of the two capacitors.

32. The property of an electric circuit that opposes any change in current is called...
800 volts.
Zero amps.
Inductance.
Derive a neutral for grounding purposes.

33. All transformers step voltage up or down by...
5:1
Current changing constantly in magnitude and periodically in direction.
Inductance.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

34. The purpose of a zig-zag transformer is to...
Nearly constant.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Potential transformer.
Derive a neutral for grounding purposes.

35. The primary function of a power transformer is to provide...
At least two phases
Full-load - three-phase voltage.
Kilovolt ampere (KVA).
X.

36. The main function of CT's and PT's on a main substation is to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Allow for metering voltage and Current.
75 turns.
X.

37. 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?
Electro-magnetism for their operation.
800 volts.
Draw less current.
1 amp.

38. What steps up or steps down AC voltage?
100 volts.
The current will read zero.
Transformer
The motor rotation is reversed.

39. 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?
Squirrel-cage rotor.
60 Hertz
3 -979 Volts.
200 volts AC.

40. 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.
The motor rotation is reversed.
Electro-magnetism for their operation.
5:1

41. 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.
Zero amps.
Because less current flowing at high voltage causes less line loss per kilowatt.
Capacitance.

42. The speed of an alternating current - squirrel-cage induction motor is...
A step-up transformer.
Inductance.
Nearly constant.
Shunted and taped

43. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
Because less current flowing at high voltage causes less line loss per kilowatt.
200 volts AC.
Capacitance.

44. What should the duty rating of a grounding resistor be?
The motor rotation is reversed.
Continuous.
A step-up transformer.
60 cycles per second (60 Hertz).

45. The size of a transformer is measured in...
Kilovolt ampere (KVA).
Derive a neutral for grounding purposes.
60 cycles per second (60 Hertz).
Transformers.

46. 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?
The capacitors should be discharged.
75 turns.
7 -630 volts.
Draw less current.

47. How should clothing be removed from a burn?
Four times less than that of the secondary.
Cut around clothing that has adhered to the burned area.
Clamp-on ammeter.
Larger than that found in the primary winding.

48. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
They should be made by the same manufacturer.
Draw less current.
25 feet.
Reverse its rotation.

49. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Squirrel-cage rotor.
Carotid pulse - which is located in the neck next to the Adam's apple.
277 volts.
Isolation transformer.

50. What is a capacitor?
Squirrel-cage rotor.
At the source transformer.
A device used to store electrical energy.
60 cycles per second (60 Hertz).