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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. Operating coils - motors - transformers - relays and solenoids depend upon...
They should be made by the same manufacturer.
The sum of the two capacitors.
Electro-magnetism for their operation.
Two speeds

2. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Transformers.
Potential transformer.
The motor rotation is reversed.
600 volts.

3. 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?
An electromagnet.
Second-degree burn.
Derive a neutral for grounding purposes.
600 volts.

4. What type of 3-phase AC motor is used most often around a mine?
The motor rotation is reversed.
Four times less than that of the secondary.
Squirrel-cage induction motor.
The current will read zero.

5. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Disconnect the frame-grounding conductor.
Stator windings.
The chest should rise or inflate.
A step-up transformer.

6. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Tied together
100 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
480 volts.

7. Current in an AC circuit may be measured by...
Clamp-on ammeter.
No.6 AWG.
Alternating current.
Four times less than that of the secondary.

8. 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...
Transformer
100 volts.
Draw less current.
An electrical shock hazard may exist.

9. 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...
Transformers.
75 turns.
100 volts.
Tied together

10. 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?
3 -979 Volts.
100 turns.
277 volts.
2000 watts

11. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
An electromagnet.
5:1.
Larger than that found in the primary winding.

12. The transformer used only to measure voltage is a...
Carotid pulse - which is located in the neck next to the Adam's apple.
5:1
Potential transformer.
Continuous.

13. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Capacitance.
Nearly constant.
Grounded phase and ground fault devices were not operating.
15 feet off the ground.

14. The primary function of a power transformer is to provide...
Second-degree burn.
Inductance.
Full-load - three-phase voltage.
100 volts.

15. What is a capacitor?
A device used to store electrical energy.
Two speeds
Potential transformer.
At least two phases

16. What is the danger when working around capacitors?
75 turns.
An electrical shock hazard may exist.
A.C.
Grounded phase and ground fault devices were not operating.

17. Where should grounding resistors be located?
150 turns.
Inductance.
Electro-magnetism for their operation.
At the source transformer.

18. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
A device used to store electrical energy.
12 to 15 times a minute.
2000 watts

19. AC voltage is raised or lowered by means of...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
They should be made by the same manufacturer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Transformers.

20. 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.
25 feet.
Capacitance.
A device used to store electrical energy.

21. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Reverse its rotation.
3 -979 Volts.
At least two phases
60 Hertz

22. The combined capacitance of two capacitors in parallel is...
Transformer
At the source transformer.
The sum of the two capacitors.
Derive a neutral for grounding purposes.

23. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Four times less than that of the secondary.
Two speeds
Short-circuited after power has been removed.
A.C.

24. 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?
200 volts AC.
3 -979 Volts.
Zero amps.
At least two phases

25. A solenoid coil is...
480 volts.
An electromagnet.
A step-up transformer.
1 amp.

26. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Provides single-phase power to smaller loads such as lights - heaters - etc.
7 -630 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
X.

27. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
200 volts AC.
Hyperventilation.
Nearly constant.

28. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Continuous.
Circuit Breaker.
The chest should rise or inflate.
Isolation transformer.

29. 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?
An electromagnet.
Zero amps.
Check to make sure that the victim is not still in contact with the electricity.
75 turns.

30. How do you change the direction of a 3-phase AC motor?
Isolation transformer.
Inductance.
No.6 AWG.
Reverse any two-phase leads.

31. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
2000 watts
At least two phases
Tied together
They should be made by the same manufacturer.

32. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Alternating current.
Kilovolt ampere (KVA).
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Second-degree burn.

33. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Inductance.
100 volts.
Lower current and higher voltage

34. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Hyperventilation.
Lower current and higher voltage
The capacitors should be discharged.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

35. 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.
At the source transformer.
A device used to store electrical energy.
A grounding resistor.

36. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
Zero amps.
Potential transformer.
The chest should rise or inflate.

37. 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...
The current will read zero.
100 volts.
Larger than that found in the primary winding.
Electro-magnetism for their operation.

38. The primary leads of a single-phase transformer should be connected to the...
Hyperventilation.
No.6 AWG.
Current that changes constantly in magnitude and periodically in direction.
H terminals.

39. The secondary windings on a 10:1 step-down transformer will have a wire size...
Inductance.
Larger than that found in the primary winding.
Check to make sure that the victim is not still in contact with the electricity.
It provides good speed control.

40. 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?
Electro-magnetism for their operation.
150 turns.
Lower current and higher voltage
Current that changes constantly in magnitude and periodically in direction.

41. How should clothing be removed from a burn?
25 feet.
A.C.
Hyperventilation.
Cut around clothing that has adhered to the burned area.

42. 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?
5:1.
75 turns.
5:1
12 to 15 times a minute.

43. What should the duty rating of a grounding resistor be?
15 feet off the ground.
Larger than that found in the primary winding.
Continuous.
5:1

44. What is the first step to be followed in aiding a victim of electrical shock?
Capacitance.
Check to make sure that the victim is not still in contact with the electricity.
Allow for metering voltage and Current.
5:1

45. A wound-rotor induction motor has all the following EXCEPT...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Squirrel-cage rotor.
480 volts.
The chest should rise or inflate.

46. At what rate should mouth-to-mouth resuscitation be applied?
Capacitance.
Four times less than that of the secondary.
Reverse any two-phase leads.
12 to 15 times a minute.

47. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
No.6 AWG.
Transformer
Four times less than that of the secondary.
A step-up transformer.

48. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
A.C.
Capacitance.
25 feet.
They should be made by the same manufacturer.

49. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Current changing constantly in magnitude and periodically in direction.
Potential transformer.
15 feet off the ground.
The current will read zero.

50. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Inductance.
No.6 AWG.
5:1.
60 cycles per second (60 Hertz).