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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 the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
At least two phases
Draw less current.
Allow for metering voltage and Current.

2. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Full-load - three-phase voltage.
Carotid pulse - which is located in the neck next to the Adam's apple.
2000 watts

3. The standard frequency of alternating current used at a mine is...
Kilovolt ampere (KVA).
Four times less than that of the secondary.
60 Hertz
150 turns.

4. Three-phase AC underground cables must be provided with overcurrent protection using a...
600 volts.
75 turns.
Circuit Breaker.
Current changing constantly in magnitude and periodically in direction.

5. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
100 volts.
Reverse any two-phase leads.
Disconnect the frame-grounding conductor.
Because less current flowing at high voltage causes less line loss per kilowatt.

6. The property of an electrical circuit that opposes any change in voltage is called...
Cut around clothing that has adhered to the burned area.
No.6 AWG.
Capacitance.
7 -630 volts.

7. 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?
Kilovolt ampere (KVA).
2000 watts
Reverse its rotation.
3 -979 Volts.

8. When not connected to a load - the secondary leads of a current transformer should be...
The chest should rise or inflate.
Shunted and taped
No.6 AWG.
A device used to store electrical energy.

9. 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
H terminals.
150 turns.
An electrical shock hazard may exist.

10. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
A step-up transformer.
Two speeds
Nearly constant.

11. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Current changing constantly in magnitude and periodically in direction.
Draw less current.
The capacitors should be discharged.
200 volts AC.

12. 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?
800 volts.
Larger than that found in the primary winding.
100 turns.
Current that changes constantly in magnitude and periodically in direction.

13. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
A step-up transformer.
60 cycles per second (60 Hertz).
480 volts.
1 amp.

14. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Continuous.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Electro-magnetism for their operation.
The chest should rise or inflate.

15. A solenoid coil is...
An electromagnet.
2000 watts
Circuit Breaker.
Short-circuited after power has been removed.

16. Not true about AC power?
The sum of the two capacitors.
Second-degree burn.
It provides good speed control.
Grounded phase and ground fault devices were not operating.

17. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Capacitance.
Four times less than that of the secondary.
1 amp.

18. 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?
150 turns.
277 volts.
800 volts.
1 amp.

19. Compared to the secondary of a loaded - step-down transformer - the primary has...
Four times less than that of the secondary.
Current changing constantly in magnitude and periodically in direction.
Lower current and higher voltage
Transformers.

20. The transformer used only to measure voltage is a...
A device used to store electrical energy.
Potential transformer.
200 volts AC.
100 volts.

21. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
A.C.
5:1.
Because less current flowing at high voltage causes less line loss per kilowatt.

22. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
277 volts.
Reverse its rotation.
The capacitors should be discharged.
25 feet.

23. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Nearly constant.
Grounded phase and ground fault devices were not operating.
Kilovolt ampere (KVA).
Larger than that found in the primary winding.

24. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Larger than that found in the primary winding.
Potential transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
7 -630 volts.

25. 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.
Draw less current.
5:1.
Four times less than that of the secondary.
Draw less current.

26. Alternating current may be defined as...
Cut around clothing that has adhered to the burned area.
480 volts.
Lower current and higher voltage.
Current that changes constantly in magnitude and periodically in direction.

27. At what rate should mouth-to-mouth resuscitation be applied?
The sum of the two capacitors.
Tied together
12 to 15 times a minute.
Four times less than that of the secondary.

28. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Transformer
100 volts.
600 volts.
No.6 AWG.

29. What steps up or steps down AC voltage?
A.C.
Transformer
An electromagnet.
Check to make sure that the victim is not still in contact with the electricity.

30. 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...
Disconnect the frame-grounding conductor.
Draw less current.
15 feet off the ground.
Circuit Breaker.

31. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Nearly constant.
X.
Lower current and higher voltage.
A grounding resistor.

32. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
25 feet.
Nearly constant.
The motor rotation is reversed.
Zero amps.

33. 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.
Squirrel-cage induction motor.
Two speeds
Transformers.

34. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Full-load - three-phase voltage.
600 volts.
Derive a neutral for grounding purposes.

35. The standard frequency of power supplied by the power company is...
Kilovolt ampere (KVA).
Stator windings.
60 cycles per second (60 Hertz).
Current changing constantly in magnitude and periodically in direction.

36. AC voltage is raised or lowered by means of...
Kilovolt ampere (KVA).
Draw less current.
480 volts.
Transformers.

37. 460 volts AC is required to operate two motors - one connected in single-phase and the other connected in three-phase. The three-phase motor will...
7 -630 volts.
Full-load - three-phase voltage.
Draw less current.
Provides single-phase power to smaller loads such as lights - heaters - etc.

38. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
Nearly constant.
60 Hertz
A grounding resistor.

39. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
3 -979 Volts.
A grounding resistor.
277 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.

40. How do you change the direction of a 3-phase AC motor?
An electrical shock hazard may exist.
Reverse any two-phase leads.
Carotid pulse - which is located in the neck next to the Adam's apple.
Lower current and higher voltage.

41. The speed of an alternating current - squirrel-cage induction motor is...
No.6 AWG.
Nearly constant.
Draw less current.
5:1.

42. The combined capacitance of two capacitors in parallel is...
Disconnect the frame-grounding conductor.
Draw less current.
Isolation transformer.
The sum of the two capacitors.

43. The purpose of a zig-zag transformer is to...
Alternating current.
Derive a neutral for grounding purposes.
75 turns.
A grounding resistor.

44. What should the duty rating of a grounding resistor be?
Disconnect the frame-grounding conductor.
Two speeds
Continuous.
Circuit Breaker.

45. A transformer with a 1:1 ratio is usually a (an)...
The current will read zero.
200 volts AC.
Isolation transformer.
Full-load - three-phase voltage.

46. The main function of CT's and PT's on a main substation is to...
800 volts.
3 -979 Volts.
Draw less current.
Allow for metering voltage and Current.

47. Not a symptom of electrical shock?.
Draw less current.
The current will read zero.
Hyperventilation.
Circuit Breaker.

48. The size of a transformer is measured in...
150 turns.
Stator windings.
Continuous.
Kilovolt ampere (KVA).

49. The primary function of a power transformer is to provide...
H terminals.
2000 watts
Full-load - three-phase voltage.
Second-degree burn.

50. 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?
75 turns.
Reverse its rotation.
An electrical shock hazard may exist.
Grounded phase and ground fault devices were not operating.