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AC Theory

Instructions:

Answer 50 questions in 30 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. High voltage is used to transmit power over long distances...
277 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
Isolation transformer.
Transformers.

2. Compared to the secondary of a loaded - step-down transformer - the primary has...
480 volts.
Lower current and higher voltage.
Kilovolt ampere (KVA).
Four times less than that of the secondary.

3. All transformers step voltage up or down by...
Inductance.
Hyperventilation.
Shunted and taped
Two speeds

4. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Alternating current.
Tied together
Lower current and higher voltage.

5. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
At the source transformer.
Four times less than that of the secondary.
277 volts.
60 Hertz

6. Where should grounding resistors be located?
Reverse any two-phase leads.
At the source transformer.
600 volts.
H terminals.

7. Operating coils - motors - transformers - relays and solenoids depend upon...
Draw less current.
Electro-magnetism for their operation.
Second-degree burn.
Isolation transformer.

8. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
They must be installed at least 7 feet above the ground.
The capacitors should be discharged.
277 volts.
Alternating current.

9. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
They should be made by the same manufacturer.
800 volts.
An electrical shock hazard may exist.

10. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
The sum of the two capacitors.
Squirrel-cage rotor.
They should be made by the same manufacturer.
Because less current flowing at high voltage causes less line loss per kilowatt.

11. 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?
Reverse its rotation.
100 turns.
Transformer
The current will read zero.

12. AC voltage is raised or lowered by means of...
Transformers.
15 feet off the ground.
1 amp.
Provides single-phase power to smaller loads such as lights - heaters - etc.

13. A burn causing a blister is classified as a...
Second-degree burn.
75 turns.
Derive a neutral for grounding purposes.
Zero amps.

14. What type of 3-phase AC motor is used most often around a mine?
Inductance.
Inductance.
It provides good speed control.
Squirrel-cage induction motor.

15. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
1 amp.
Cut around clothing that has adhered to the burned area.
Reverse its rotation.
480 volts.

16. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
No.6 AWG.
15 feet off the ground.
The chest should rise or inflate.
1 amp.

17. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
5:1
A grounding resistor.
They must be installed at least 7 feet above the ground.
Tied together

18. What is the danger when working around capacitors?
Larger than that found in the primary winding.
An electrical shock hazard may exist.
Two speeds
Check to make sure that the victim is not still in contact with the electricity.

19. 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...
A grounding resistor.
Draw less current.
Hyperventilation.
Reverse its rotation.

20. 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.
600 volts.
The motor rotation is reversed.
15 feet off the ground.
5:1.

21. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Kilovolt ampere (KVA).
2000 watts
The capacitors should be discharged.
Full-load - three-phase voltage.

22. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
They must be installed at least 7 feet above the ground.
X.
Larger than that found in the primary winding.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

23. A wound-rotor induction motor has all the following EXCEPT...
Hyperventilation.
Squirrel-cage rotor.
277 volts.
600 volts.

24. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
Capacitance.
The chest should rise or inflate.
Continuous.

25. 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.
The capacitors should be discharged.
60 Hertz
2000 watts

26. The property of an electric circuit that opposes any change in current is called...
Inductance.
480 volts.
Kilovolt ampere (KVA).
Alternating current.

27. The speed of an alternating current - squirrel-cage induction motor is...
Second-degree burn.
200 volts AC.
Nearly constant.
They must be installed at least 7 feet above the ground.

28. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
A step-up transformer.
Nearly constant.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Disconnect the frame-grounding conductor.

29. The standard frequency of alternating current used at a mine is...
Nearly constant.
Zero amps.
60 Hertz
Squirrel-cage rotor.

30. The size of a transformer is measured in...
Kilovolt ampere (KVA).
60 cycles per second (60 Hertz).
A.C.
Circuit Breaker.

31. Not an acceptable method for the installations of surface transformers?
Grounded phase and ground fault devices were not operating.
They must be installed at least 7 feet above the ground.
Reverse its rotation.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

32. 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?
Capacitance.
150 turns.
100 turns.
Allow for metering voltage and Current.

33. The purpose of a zig-zag transformer is to...
Allow for metering voltage and Current.
Capacitance.
Clamp-on ammeter.
Derive a neutral for grounding purposes.

34. What type motor is a wound-rotor induction motor?
800 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
A.C.
Stator windings.

35. 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...
No.6 AWG.
Clamp-on ammeter.
Draw less current.
Four times less than that of the secondary.

36. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
X.
Zero amps.
A device used to store electrical energy.

37. The combined capacitance of two capacitors in parallel is...
Because less current flowing at high voltage causes less line loss per kilowatt.
5:1.
Inductance.
The sum of the two capacitors.

38. A solenoid coil is...
An electromagnet.
5:1.
Electro-magnetism for their operation.
Reverse any two-phase leads.

39. 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?
1 amp.
800 volts.
60 Hertz
Disconnect the frame-grounding conductor.

40. How do you change the direction of a 3-phase AC motor?
480 volts.
Grounded phase and ground fault devices were not operating.
Reverse any two-phase leads.
Tied together

41. What is a capacitor?
7 -630 volts.
A device used to store electrical energy.
A.C.
An electrical shock hazard may exist.

42. Alternating current may be defined as...
Reverse any two-phase leads.
H terminals.
Continuous.
Current that changes constantly in magnitude and periodically in direction.

43. The primary leads of a single-phase transformer should be connected to the...
H terminals.
600 volts.
100 turns.
Electro-magnetism for their operation.

44. What steps up or steps down AC voltage?
Short-circuited after power has been removed.
It provides good speed control.
200 volts AC.
Transformer

45. 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...
7 -630 volts.
Cut around clothing that has adhered to the burned area.
Tied together
Because less current flowing at high voltage causes less line loss per kilowatt.

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

47. What should the duty rating of a grounding resistor be?
15 feet off the ground.
Continuous.
Lower current and higher voltage
25 feet.

48. 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.
Cut around clothing that has adhered to the burned area.
Current changing constantly in magnitude and periodically in direction.
Hyperventilation.

49. 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.
A device used to store electrical energy.
Larger than that found in the primary winding.
60 cycles per second (60 Hertz).

50. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Continuous.
Hyperventilation.
25 feet.