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AC Theory

Instructions:

Answer 50 questions in 20 minutes. 2 minutes extra for reading the instructions.
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?
Second-degree burn.
A device used to store electrical energy.
Allow for metering voltage and Current.
Continuous.

2. 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...
Four times less than that of the secondary.
75 turns.
Draw less current.
Current that changes constantly in magnitude and periodically in direction.

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

4. How should clothing be removed from a burn?
Derive a neutral for grounding purposes.
Inductance.
Cut around clothing that has adhered to the burned area.
60 cycles per second (60 Hertz).

5. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Two speeds
The motor rotation is reversed.
A step-up transformer.
100 volts.

6. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
1 amp.
They must be installed at least 7 feet above the ground.
Inductance.
480 volts.

7. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Hyperventilation.
25 feet.
1 amp.
Clamp-on ammeter.

8. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Kilovolt ampere (KVA).
Disconnect the frame-grounding conductor.
Lower current and higher voltage
They should be made by the same manufacturer.

9. When not connected to a load - the secondary leads of a current transformer should be...
Reverse any two-phase leads.
A.C.
Shunted and taped
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.
Derive a neutral for grounding purposes.
5:1.
100 turns.
A device used to store electrical energy.

11. The standard frequency of alternating current used at a mine is...
Draw less current.
60 Hertz
Continuous.
12 to 15 times a minute.

12. A burn causing a blister is classified as a...
Draw less current.
They must be installed at least 7 feet above the ground.
Second-degree burn.
60 Hertz

13. Alternating current may be defined as...
Full-load - three-phase voltage.
480 volts.
Current that changes constantly in magnitude and periodically in direction.
Isolation transformer.

14. To protect against over-current in a three-phase circuit over-current protection must be provided for...
12 to 15 times a minute.
They must be installed at least 7 feet above the ground.
Squirrel-cage rotor.
At least two phases

15. Which of the following does a squirrel cage induction motor have?
Stator windings.
Capacitance.
Carotid pulse - which is located in the neck next to the Adam's apple.
An electromagnet.

16. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Carotid pulse - which is located in the neck next to the Adam's apple.
12 to 15 times a minute.
X.

17. The secondary windings on a 10:1 step-down transformer will have a wire size...
Cut around clothing that has adhered to the burned area.
Grounded phase and ground fault devices were not operating.
Circuit Breaker.
Larger than that found in the primary winding.

18. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
2000 watts
Two speeds
7 -630 volts.
Hyperventilation.

19. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
The sum of the two capacitors.
X.
60 Hertz
Full-load - three-phase voltage.

20. 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?
The motor rotation is reversed.
60 Hertz
3 -979 Volts.
Circuit Breaker.

21. 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?
H terminals.
Stator windings.
An electromagnet.
75 turns.

22. Current that changes periodically in direction is...
Lower current and higher voltage
The sum of the two capacitors.
Alternating current.
Check to make sure that the victim is not still in contact with the electricity.

23. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
25 feet.
The chest should rise or inflate.
Transformer
Derive a neutral for grounding purposes.

24. The purpose of a zig-zag transformer is to...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Cut around clothing that has adhered to the burned area.
150 turns.
Derive a neutral for grounding purposes.

25. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
They must be installed at least 7 feet above the ground.
1 amp.
Lower current and higher voltage.
Continuous.

26. 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?
A.C.
An electrical shock hazard may exist.
150 turns.
Full-load - three-phase voltage.

27. 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?
75 turns.
3 -979 Volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Two speeds

28. Where should grounding resistors be located?
H terminals.
Electro-magnetism for their operation.
At the source transformer.
480 volts.

29. 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...
Zero amps.
Electro-magnetism for their operation.
100 volts.
Hyperventilation.

30. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
7 -630 volts.
800 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
Draw less current.

31. A control power transformer...
Stator windings.
1 amp.
60 cycles per second (60 Hertz).
Provides single-phase power to smaller loads such as lights - heaters - etc.

32. What type motor is a wound-rotor induction motor?
Second-degree burn.
Lower current and higher voltage
A.C.
Grounded phase and ground fault devices were not operating.

33. The property of an electric circuit that opposes any change in current is called...
The sum of the two capacitors.
Reverse its rotation.
Inductance.
Carotid pulse - which is located in the neck next to the Adam's apple.

34. Current in an AC circuit may be measured by...
They should be made by the same manufacturer.
Two speeds
Clamp-on ammeter.
An electrical shock hazard may exist.

35. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Isolation transformer.
Inductance.
Transformers.

36. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Shunted and taped
5:1
Isolation transformer.

37. A solenoid coil is...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The chest should rise or inflate.
3 -979 Volts.
An electromagnet.

38. AC voltage is raised or lowered by means of...
Transformers.
Alternating current.
277 volts.
The chest should rise or inflate.

39. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Reverse its rotation.
Circuit Breaker.
15 feet off the ground.
Transformer

40. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because less current flowing at high voltage causes less line loss per kilowatt.
Shunted and taped
Squirrel-cage induction motor.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

41. 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...
Draw less current.
Two speeds
Four times less than that of the secondary.
Capacitance.

42. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
5:1
Cut around clothing that has adhered to the burned area.
The sum of the two capacitors.

43. A 3-phase - 2 speed - constant torque motor is running at fast speed. The motor windings are connected wye for fast speed. Motor leads T4 - T5 and T6 are connected to the line leads. Motor leads T1 - T2 and T3 should be...
Tied together
A grounding resistor.
A device used to store electrical energy.
Full-load - three-phase voltage.

44. The speed of an alternating current - squirrel-cage induction motor is...
Kilovolt ampere (KVA).
800 volts.
Nearly constant.
Squirrel-cage rotor.

45. What type of 3-phase AC motor is used most often around a mine?
Circuit Breaker.
Squirrel-cage induction motor.
An electromagnet.
The chest should rise or inflate.

46. 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.
Hyperventilation.
277 volts.
At the source transformer.

47. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Inductance.
A grounding resistor.
Continuous.
Provides single-phase power to smaller loads such as lights - heaters - etc.

48. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
They should be made by the same manufacturer.
The chest should rise or inflate.
Cut around clothing that has adhered to the burned area.
2000 watts

49. If any two-phase wires are reversed on a three-phase motor - the motor will...
They must be installed at least 7 feet above the ground.
Lower current and higher voltage.
Reverse its rotation.
Two speeds

50. Not a symptom of electrical shock?.
Cut around clothing that has adhered to the burned area.
Hyperventilation.
The chest should rise or inflate.
Shunted and taped