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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. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
Lower current and higher voltage.
15 feet off the ground.
480 volts.

2. When not connected to a load - the secondary leads of a current transformer should be...
Cut around clothing that has adhered to the burned area.
The motor rotation is reversed.
Check to make sure that the victim is not still in contact with the electricity.
Shunted and taped

3. Alternating current may be defined as...
Continuous.
Current that changes constantly in magnitude and periodically in direction.
Draw less current.
Shunted and taped

4. AC voltage is raised or lowered by means of...
Tied together
Draw less current.
Transformers.
An electrical shock hazard may exist.

5. All transformers step voltage up or down by...
60 cycles per second (60 Hertz).
Inductance.
Carotid pulse - which is located in the neck next to the Adam's apple.
Hyperventilation.

6. Current that changes periodically in direction is...
Grounded phase and ground fault devices were not operating.
A step-up transformer.
A grounding resistor.
Alternating current.

7. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
The sum of the two capacitors.
Capacitance.
Shunted and taped

8. A burn causing a blister is classified as a...
75 turns.
Second-degree burn.
200 volts AC.
100 volts.

9. Where should grounding resistors be located?
It provides good speed control.
Reverse any two-phase leads.
Full-load - three-phase voltage.
At the source transformer.

10. What is the first step to be followed in aiding a victim of electrical shock?
Squirrel-cage rotor.
Transformers.
Check to make sure that the victim is not still in contact with the electricity.
Inductance.

11. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
5:1.
At least two phases
Grounded phase and ground fault devices were not operating.
12 to 15 times a minute.

12. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Circuit Breaker.
A grounding resistor.
Inductance.
An electromagnet.

13. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
X.
800 volts.
An electromagnet.

14. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
3 -979 Volts.
277 volts.
600 volts.

15. 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.
Inductance.
Allow for metering voltage and Current.
277 volts.

16. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
15 feet off the ground.
Alternating current.
Current changing constantly in magnitude and periodically in direction.

17. The transformer used only to measure voltage is a...
Because less current flowing at high voltage causes less line loss per kilowatt.
Nearly constant.
25 feet.
Potential transformer.

18. 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...
100 turns.
5:1
Draw less current.
Tied together

19. What should the duty rating of a grounding resistor be?
Continuous.
Larger than that found in the primary winding.
The capacitors should be discharged.
75 turns.

20. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Continuous.
An electromagnet.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Circuit Breaker.

21. Not a symptom of electrical shock?.
Stator windings.
3 -979 Volts.
Hyperventilation.
The motor rotation is reversed.

22. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
12 to 15 times a minute.
Because less current flowing at high voltage causes less line loss per kilowatt.
Current changing constantly in magnitude and periodically in direction.
480 volts.

23. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Reverse any two-phase leads.
They should be made by the same manufacturer.
1 amp.
277 volts.

24. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
An electrical shock hazard may exist.
Clamp-on ammeter.
75 turns.
277 volts.

25. 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?
Draw less current.
3 -979 Volts.
A step-up transformer.
Disconnect the frame-grounding conductor.

26. 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
Lower current and higher voltage
Stator windings.
Short-circuited after power has been removed.

27. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Because less current flowing at high voltage causes less line loss per kilowatt.
800 volts.
25 feet.
A grounding resistor.

28. 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 motor rotation is reversed.
Current changing constantly in magnitude and periodically in direction.
It provides good speed control.
5:1.

29. The property of an electric circuit that opposes any change in current is called...
Nearly constant.
Inductance.
Transformer
It provides good speed control.

30. 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 any two-phase leads.
100 turns.
3 -979 Volts.
A grounding resistor.

31. If any two-phase wires are reversed on a three-phase motor - the motor will...
Short-circuited after power has been removed.
At least two phases
Allow for metering voltage and Current.
Reverse its rotation.

32. What type motor is a wound-rotor induction motor?
Cut around clothing that has adhered to the burned area.
A.C.
60 cycles per second (60 Hertz).
X.

33. 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?
Capacitance.
75 turns.
Transformers.
200 volts AC.

34. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
12 to 15 times a minute.
150 turns.
60 cycles per second (60 Hertz).

35. 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?
150 turns.
Clamp-on ammeter.
The motor rotation is reversed.
Shunted and taped

36. 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...
Lower current and higher voltage
Draw less current.
The current will read zero.
Two speeds

37. Which of the following does a squirrel cage induction motor have?
Nearly constant.
Reverse any two-phase leads.
5:1
Stator windings.

38. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
75 turns.
No.6 AWG.
It provides good speed control.
Disconnect the frame-grounding conductor.

39. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Cut around clothing that has adhered to the burned area.
7 -630 volts.
The current will read zero.
Kilovolt ampere (KVA).

40. The size of a transformer is measured in...
200 volts AC.
Kilovolt ampere (KVA).
Draw less current.
2000 watts

41. What is a capacitor?
277 volts.
A device used to store electrical energy.
Full-load - three-phase voltage.
Continuous.

42. The speed of an alternating current - squirrel-cage induction motor is...
Reverse any two-phase leads.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Shunted and taped
Nearly constant.

43. The primary leads of a single-phase transformer should be connected to the...
Current that changes constantly in magnitude and periodically in direction.
It provides good speed control.
H terminals.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

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

45. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
They should be made by the same manufacturer.
1 amp.
Alternating current.
Lower current and higher voltage

46. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
At least two phases
A device used to store electrical energy.
5:1.

47. The purpose of a zig-zag transformer is to...
5:1
Reverse its rotation.
Check to make sure that the victim is not still in contact with the electricity.
Derive a neutral for grounding purposes.

48. How should clothing be removed from a burn?
Four times less than that of the secondary.
Draw less current.
800 volts.
Cut around clothing that has adhered to the burned area.

49. 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?
277 volts.
60 cycles per second (60 Hertz).
Potential transformer.
75 turns.

50. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Current changing constantly in magnitude and periodically in direction.
Zero amps.
5:1.
Kilovolt ampere (KVA).