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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. 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?
A device used to store electrical energy.
12 to 15 times a minute.
Clamp-on ammeter.
75 turns.

2. Where should grounding resistors be located?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Reverse its rotation.
At the source transformer.
Continuous.

3. 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.
Clamp-on ammeter.
Squirrel-cage rotor.
7 -630 volts.

4. What should the duty rating of a grounding resistor be?
75 turns.
Continuous.
Inductance.
Lower current and higher voltage.

5. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
A grounding resistor.
Inductance.
Hyperventilation.

6. The standard frequency of alternating current used at a mine is...
60 Hertz
100 turns.
A device used to store electrical energy.
5:1.

7. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
Hyperventilation.
The chest should rise or inflate.
150 turns.

8. 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.
5:1
5:1.
Isolation transformer.
100 volts.

9. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
Second-degree burn.
The motor rotation is reversed.
Short-circuited after power has been removed.

10. The main function of CT's and PT's on a main substation is to...
The capacitors should be discharged.
Allow for metering voltage and Current.
Transformer
It provides good speed control.

11. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Transformers.
The chest should rise or inflate.
75 turns.
150 turns.

12. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
Inductance.
Two speeds
Clamp-on ammeter.

13. The speed of an alternating current - squirrel-cage induction motor is...
75 turns.
It provides good speed control.
Nearly constant.
Shunted and taped

14. What type of 3-phase AC motor is used most often around a mine?
Second-degree burn.
480 volts.
Squirrel-cage induction motor.
Derive a neutral for grounding purposes.

15. 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 electromagnet.
Current that changes constantly in magnitude and periodically in direction.
Second-degree burn.

16. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Current changing constantly in magnitude and periodically in direction.
Short-circuited after power has been removed.
Derive a neutral for grounding purposes.

17. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Nearly constant.
Four times less than that of the secondary.
Alternating current.
At the source transformer.

18. 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?
Second-degree burn.
200 volts AC.
1 amp.
Carotid pulse - which is located in the neck next to the Adam's apple.

19. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
X.
100 volts.
Squirrel-cage rotor.
277 volts.

20. 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...
Shunted and taped
Draw less current.
Disconnect the frame-grounding conductor.
25 feet.

21. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Squirrel-cage induction motor.
Inductance.
H terminals.
Disconnect the frame-grounding conductor.

22. What is a capacitor?
They must be installed at least 7 feet above the ground.
Stator windings.
5:1
A device used to store electrical energy.

23. 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...
Potential transformer.
100 volts.
Reverse its rotation.
Transformers.

24. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
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.
Lower current and higher voltage

25. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
Current changing constantly in magnitude and periodically in direction.
Short-circuited after power has been removed.
Because less current flowing at high voltage causes less line loss per kilowatt.

26. What type motor is a wound-rotor induction motor?
A.C.
800 volts.
Derive a neutral for grounding purposes.
12 to 15 times a minute.

27. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Draw less current.
The current will read zero.
Continuous.
Lower current and higher voltage.

28. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
5:1.
Cut around clothing that has adhered to the burned area.
Two speeds
Carotid pulse - which is located in the neck next to the Adam's apple.

29. The primary leads of a single-phase transformer should be connected to the...
It provides good speed control.
H terminals.
Hyperventilation.
150 turns.

30. A transformer with a 1:1 ratio is usually a (an)...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Allow for metering voltage and Current.
Reverse any two-phase leads.
Isolation transformer.

31. Not true about AC power?
Circuit Breaker.
The capacitors should be discharged.
It provides good speed control.
Grounded phase and ground fault devices were not operating.

32. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Hyperventilation.
Full-load - three-phase voltage.
5:1
2000 watts

33. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
At the source transformer.
25 feet.
An electromagnet.
No.6 AWG.

34. 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.
H terminals.
Two speeds
100 turns.

35. The property of an electric circuit that opposes any change in current is called...
They must be installed at least 7 feet above the ground.
100 volts.
Inductance.
Hyperventilation.

36. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Grounded phase and ground fault devices were not operating.
A step-up transformer.
Full-load - three-phase voltage.
Check to make sure that the victim is not still in contact with the electricity.

37. 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.
X.
15 feet off the ground.
Alternating current.

38. Compared to the secondary of a loaded - step-down transformer - the primary has...
Cut around clothing that has adhered to the burned area.
Continuous.
Lower current and higher voltage.
Current that changes constantly in magnitude and periodically in direction.

39. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Grounded phase and ground fault devices were not operating.
5:1
Transformers.
It provides good speed control.

40. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
12 to 15 times a minute.
75 turns.
No.6 AWG.

41. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
The chest should rise or inflate.
Grounded phase and ground fault devices were not operating.
480 volts.
Disconnect the frame-grounding conductor.

42. Not an acceptable method for the installations of surface transformers?
12 to 15 times a minute.
They must be installed at least 7 feet above the ground.
Lower current and higher voltage.
Transformers.

43. A solenoid coil is...
Electro-magnetism for their operation.
60 cycles per second (60 Hertz).
An electromagnet.
Carotid pulse - which is located in the neck next to the Adam's apple.

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

45. What is the danger when working around capacitors?
15 feet off the ground.
Inductance.
An electrical shock hazard may exist.
Cut around clothing that has adhered to the burned area.

46. Alternating current may be defined as...
Reverse any two-phase leads.
Electro-magnetism for their operation.
Squirrel-cage rotor.
Current that changes constantly in magnitude and periodically in direction.

47. The size of a transformer is measured in...
X.
Kilovolt ampere (KVA).
An electromagnet.
At the source transformer.

48. When not connected to a load - the secondary leads of a current transformer should be...
A device used to store electrical energy.
Current that changes constantly in magnitude and periodically in direction.
7 -630 volts.
Shunted and taped

49. The purpose of a zig-zag transformer is to...
A grounding resistor.
Second-degree burn.
Clamp-on ammeter.
Derive a neutral for grounding purposes.

50. A wound-rotor induction motor has all the following EXCEPT...
3 -979 Volts.
100 turns.
Current that changes constantly in magnitude and periodically in direction.
Squirrel-cage rotor.