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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 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Cut around clothing that has adhered to the burned area.
Grounded phase and ground fault devices were not operating.
2000 watts
600 volts.

2. 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...
800 volts.
100 volts.
100 turns.
Hyperventilation.

3. The standard frequency of alternating current used at a mine is...
Four times less than that of the secondary.
No.6 AWG.
25 feet.
60 Hertz

4. 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.
No.6 AWG.
75 turns.
At the source transformer.

5. The speed of an alternating current - squirrel-cage induction motor is...
Reverse its rotation.
277 volts.
Nearly constant.
60 cycles per second (60 Hertz).

6. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
Four times less than that of the secondary.
Derive a neutral for grounding purposes.
Draw less current.

7. 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.
277 volts.
Reverse any two-phase leads.
100 volts.

8. The transformer used only to measure voltage is a...
Electro-magnetism for their operation.
Because less current flowing at high voltage causes less line loss per kilowatt.
Potential transformer.
Cut around clothing that has adhered to the burned area.

9. Compared to the secondary of a loaded - step-down transformer - the primary has...
The sum of the two capacitors.
Short-circuited after power has been removed.
Lower current and higher voltage.
60 cycles per second (60 Hertz).

10. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Electro-magnetism for their operation.
277 volts.
Clamp-on ammeter.
Allow for metering voltage and Current.

11. How do you change the direction of a 3-phase AC motor?
An electrical shock hazard may exist.
Reverse any two-phase leads.
A device used to store electrical energy.
The sum of the two capacitors.

12. 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?
The capacitors should be discharged.
Alternating current.
The motor rotation is reversed.
150 turns.

13. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
The capacitors should be discharged.
Short-circuited after power has been removed.
Transformers.

14. 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?
Transformer
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Continuous.
3 -979 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?
Squirrel-cage rotor.
60 Hertz
75 turns.
5:1.

16. 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.
60 cycles per second (60 Hertz).
75 turns.
An electromagnet.

17. A wound-rotor induction motor has all the following EXCEPT...
An electromagnet.
1 amp.
A.C.
Squirrel-cage rotor.

18. What type of 3-phase AC motor is used most often around a mine?
H terminals.
Allow for metering voltage and Current.
Squirrel-cage induction motor.
Reverse its rotation.

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

20. What is the first step to be followed in aiding a victim of electrical shock?
Four times less than that of the secondary.
Stator windings.
Check to make sure that the victim is not still in contact with the electricity.
A grounding resistor.

21. What is a capacitor?
A device used to store electrical energy.
They must be installed at least 7 feet above the ground.
Cut around clothing that has adhered to the burned area.
The current will read zero.

22. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
An electromagnet.
Current that changes constantly in magnitude and periodically in direction.
Tied together
Short-circuited after power has been removed.

23. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Alternating current.
X.
An electromagnet.
5:1.

24. AC voltage is raised or lowered by means of...
At least two phases
800 volts.
600 volts.
Transformers.

25. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
15 feet off the ground.
Check to make sure that the victim is not still in contact with the electricity.
100 volts.

26. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Cut around clothing that has adhered to the burned area.
Transformers.
The chest should rise or inflate.
The motor rotation is reversed.

27. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Allow for metering voltage and Current.
Two speeds
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Transformers.

28. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
100 volts.
Larger than that found in the primary winding.
Inductance.
A step-up transformer.

29. Find the turns ratio of a single-phase transformer with the following values: Primary power of 5KW - secondary current of 100 amps - and primary voltage of 250 volts.
5:1
12 to 15 times a minute.
Tied together
Potential transformer.

30. Three-phase AC underground cables must be provided with overcurrent protection using a...
Nearly constant.
An electromagnet.
Circuit Breaker.
7 -630 volts.

31. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
It provides good speed control.
100 turns.
The capacitors should be discharged.

32. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Clamp-on ammeter.
Kilovolt ampere (KVA).
At least two phases
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

33. Define alternating current...
A device used to store electrical energy.
An electromagnet.
277 volts.
Current changing constantly in magnitude and periodically in direction.

34. What type motor is a wound-rotor induction motor?
Reverse any two-phase leads.
Grounded phase and ground fault devices were not operating.
Transformers.
A.C.

35. A control power transformer...
They must be installed at least 7 feet above the ground.
Lower current and higher voltage
The motor rotation is reversed.
Provides single-phase power to smaller loads such as lights - heaters - etc.

36. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
200 volts AC.
H terminals.
15 feet off the ground.
The motor rotation is reversed.

37. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
A.C.
Current changing constantly in magnitude and periodically in direction.
2000 watts

38. 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?
200 volts AC.
3 -979 Volts.
75 turns.
Two speeds

39. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Inductance.
5:1.
1 amp.

40. The primary leads of a single-phase transformer should be connected to the...
It provides good speed control.
Current changing constantly in magnitude and periodically in direction.
H terminals.
Short-circuited after power has been removed.

41. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
At least two phases
Disconnect the frame-grounding conductor.
Shunted and taped

42. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Cut around clothing that has adhered to the burned area.
7 -630 volts.
Clamp-on ammeter.
Grounded phase and ground fault devices were not operating.

43. The combined capacitance of two capacitors in parallel is...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
1 amp.
The sum of the two capacitors.
Inductance.

44. The purpose of a zig-zag transformer is to...
Kilovolt ampere (KVA).
150 turns.
75 turns.
Derive a neutral for grounding purposes.

45. The size of a transformer is measured in...
Inductance.
Kilovolt ampere (KVA).
480 volts.
Second-degree burn.

46. Not a symptom of electrical shock?.
Hyperventilation.
5:1.
At least two phases
The motor rotation is reversed.

47. 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?
Cut around clothing that has adhered to the burned area.
Reverse its rotation.
Tied together
75 turns.

48. A burn causing a blister is classified as a...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
480 volts.
Second-degree burn.
Kilovolt ampere (KVA).

49. Not true about AC power?
At least two phases
It provides good speed control.
They should be made by the same manufacturer.
75 turns.

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