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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 is a capacitor?
75 turns.
12 to 15 times a minute.
200 volts AC.
A device used to store electrical energy.

2. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Disconnect the frame-grounding conductor.
200 volts AC.
At the source transformer.
The chest should rise or inflate.

3. 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?
200 volts AC.
150 turns.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Lower current and higher voltage.

4. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Reverse any two-phase leads.
600 volts.
Grounded phase and ground fault devices were not operating.
The motor rotation is reversed.

5. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
480 volts.
Clamp-on ammeter.
60 Hertz

6. What should the duty rating of a grounding resistor be?
A device used to store electrical energy.
15 feet off the ground.
Continuous.
60 Hertz

7. How should clothing be removed from a burn?
Alternating current.
Cut around clothing that has adhered to the burned area.
Current that changes constantly in magnitude and periodically in direction.
5:1

8. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
3 -979 Volts.
Two speeds
A.C.
Disconnect the frame-grounding conductor.

9. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
H terminals.
Cut around clothing that has adhered to the burned area.
Short-circuited after power has been removed.
100 volts.

10. How do you change the direction of a 3-phase AC motor?
60 cycles per second (60 Hertz).
100 volts.
The current will read zero.
Reverse any two-phase leads.

11. The primary function of a power transformer is to provide...
Second-degree burn.
Full-load - three-phase voltage.
The chest should rise or inflate.
Grounded phase and ground fault devices were not operating.

12. High voltage is used to transmit power over long distances...
60 cycles per second (60 Hertz).
Carotid pulse - which is located in the neck next to the Adam's apple.
2000 watts
Because less current flowing at high voltage causes less line loss per kilowatt.

13. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
1 amp.
Continuous.
Alternating current.

14. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
7 -630 volts.
5:1
Allow for metering voltage and Current.
15 feet off the ground.

15. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Inductance.
75 turns.
X.

16. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Circuit Breaker.
1 amp.
25 feet.
5:1

17. The speed of an alternating current - squirrel-cage induction motor is...
An electromagnet.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The motor rotation is reversed.
Nearly constant.

18. AC voltage is raised or lowered by means of...
25 feet.
Shunted and taped
Transformers.
Nearly constant.

19. What type of 3-phase AC motor is used most often around a mine?
The sum of the two capacitors.
Squirrel-cage induction motor.
The current will read zero.
Inductance.

20. The secondary windings on a 10:1 step-down transformer will have a wire size...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Larger than that found in the primary winding.
Short-circuited after power has been removed.
Draw less current.

21. What is the first step to be followed in aiding a victim of electrical shock?
Current that changes constantly in magnitude and periodically in direction.
Check to make sure that the victim is not still in contact with the electricity.
A device used to store electrical energy.
An electrical shock hazard may exist.

22. The combined capacitance of two capacitors in parallel is...
Short-circuited after power has been removed.
The sum of the two capacitors.
100 turns.
Kilovolt ampere (KVA).

23. The property of an electrical circuit that opposes any change in voltage is called...
1 amp.
Current changing constantly in magnitude and periodically in direction.
60 Hertz
Capacitance.

24. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Nearly constant.
A step-up transformer.
Isolation transformer.
Shunted and taped

25. Current transformers - or CT's - are used to...
H terminals.
An electromagnet.
Current that changes constantly in magnitude and periodically in direction.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

26. Define alternating current...
100 turns.
600 volts.
3 -979 Volts.
Current changing constantly in magnitude and periodically in direction.

27. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Derive a neutral for grounding purposes.
Grounded phase and ground fault devices were not operating.
277 volts.
Two speeds

28. What steps up or steps down AC voltage?
Current changing constantly in magnitude and periodically in direction.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Transformer
The motor rotation is reversed.

29. Alternating current may be defined as...
Lower current and higher voltage.
Current that changes constantly in magnitude and periodically in direction.
Lower current and higher voltage
60 Hertz

30. A burn causing a blister is classified as a...
Kilovolt ampere (KVA).
A.C.
Second-degree burn.
Larger than that found in the primary winding.

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.
The sum of the two capacitors.
5:1.
Check to make sure that the victim is not still in contact with the electricity.
Stator windings.

32. The transformer used only to measure voltage is a...
A device used to store electrical energy.
Potential transformer.
Squirrel-cage rotor.
Electro-magnetism for their operation.

33. If any two-phase wires are reversed on a three-phase motor - the motor will...
An electrical shock hazard may exist.
Reverse its rotation.
X.
150 turns.

34. When not connected to a load - the secondary leads of a current transformer should be...
3 -979 Volts.
Shunted and taped
X.
Check to make sure that the victim is not still in contact with the electricity.

35. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
Derive a neutral for grounding purposes.
Draw less current.
Transformers.

36. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
1 amp.
A step-up transformer.
Electro-magnetism for their operation.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

37. Three-phase AC underground cables must be provided with overcurrent protection using a...
Disconnect the frame-grounding conductor.
Circuit Breaker.
Four times less than that of the secondary.
Clamp-on ammeter.

38. 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?
75 turns.
X.
A.C.
3 -979 Volts.

39. 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...
Draw less current.
800 volts.
100 volts.
They must be installed at least 7 feet above the ground.

40. 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?
12 to 15 times a minute.
Potential transformer.
800 volts.
A grounding resistor.

41. Current in an AC circuit may be measured by...
Clamp-on ammeter.
A.C.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
3 -979 Volts.

42. 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?
Larger than that found in the primary winding.
Reverse its rotation.
They should be made by the same manufacturer.
100 turns.

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

44. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The current will read zero.
The motor rotation is reversed.
A grounding resistor.
100 volts.

45. All transformers step voltage up or down by...
Inductance.
At the source transformer.
Zero amps.
200 volts AC.

46. What is the danger when working around capacitors?
Shunted and taped
Inductance.
Allow for metering voltage and Current.
An electrical shock hazard may exist.

47. Which of the following does a squirrel cage induction motor have?
Grounded phase and ground fault devices were not operating.
Second-degree burn.
Tied together
Stator windings.

48. A control power transformer...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Current that changes constantly in magnitude and periodically in direction.

49. Not an acceptable method for the installations of surface transformers?
5:1.
Carotid pulse - which is located in the neck next to the Adam's apple.
They must be installed at least 7 feet above the ground.
Circuit Breaker.

50. 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?
600 volts.
An electrical shock hazard may exist.
Continuous.
5:1.