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

2. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
They must be installed at least 7 feet above the ground.
Inductance.
Isolation transformer.
The chest should rise or inflate.

3. What should the duty rating of a grounding resistor be?
Reverse its rotation.
Continuous.
Cut around clothing that has adhered to the burned area.
25 feet.

4. When not connected to a load - the secondary leads of a current transformer should be...
Reverse any two-phase leads.
Circuit Breaker.
Shunted and taped
Short-circuited after power has been removed.

5. Current in an AC circuit may be measured by...
Nearly constant.
Circuit Breaker.
12 to 15 times a minute.
Clamp-on ammeter.

6. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Reverse any two-phase leads.
Current that changes constantly in magnitude and periodically in direction.
A step-up transformer.

7. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
800 volts.
Hyperventilation.
At the source transformer.
They should be made by the same manufacturer.

8. 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 current will read zero.
5:1.
Disconnect the frame-grounding conductor.
150 turns.

9. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
A.C.
The motor rotation is reversed.
Four times less than that of the secondary.
12 to 15 times a minute.

10. Operating coils - motors - transformers - relays and solenoids depend upon...
Tied together
A device used to store electrical energy.
480 volts.
Electro-magnetism for their operation.

11. 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.
Squirrel-cage induction motor.
Lower current and higher voltage.
A grounding resistor.
5:1

12. How do you change the direction of a 3-phase AC motor?
Lower current and higher voltage
Reverse any two-phase leads.
3 -979 Volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

13. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Lower current and higher voltage.
5:1.
H terminals.

14. 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...
2000 watts
Kilovolt ampere (KVA).
Electro-magnetism for their operation.
Tied together

15. 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?
100 turns.
5:1
60 Hertz
Kilovolt ampere (KVA).

16. At what rate should mouth-to-mouth resuscitation be applied?
Continuous.
Reverse its rotation.
7 -630 volts.
12 to 15 times a minute.

17. Where should grounding resistors be located?
Current that changes constantly in magnitude and periodically in direction.
Provides single-phase power to smaller loads such as lights - heaters - etc.
At the source transformer.
Two speeds

18. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Reverse its rotation.
60 cycles per second (60 Hertz).
At the source transformer.
X.

19. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
They should be made by the same manufacturer.
Disconnect the frame-grounding conductor.
No.6 AWG.

20. Not true about AC power?
5:1.
It provides good speed control.
At least two phases
A device used to store electrical energy.

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?
Zero amps.
Transformers.
75 turns.
25 feet.

22. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
Inductance.
Tied together
Alternating current.

23. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Disconnect the frame-grounding conductor.
Current changing constantly in magnitude and periodically in direction.
Reverse its rotation.

24. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
100 volts.
480 volts.
Inductance.

25. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
At the source transformer.
Disconnect the frame-grounding conductor.
600 volts.

26. Not a symptom of electrical shock?.
Continuous.
100 volts.
They should be made by the same manufacturer.
Hyperventilation.

27. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
3 -979 Volts.
Two speeds
A step-up transformer.
Allow for metering voltage and Current.

28. The standard frequency of alternating current used at a mine is...
60 Hertz
Continuous.
Draw less current.
480 volts.

29. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
Shunted and taped
60 cycles per second (60 Hertz).
Nearly constant.

30. How should clothing be removed from a burn?
Because less current flowing at high voltage causes less line loss per kilowatt.
Squirrel-cage rotor.
Circuit Breaker.
Cut around clothing that has adhered to the burned area.

31. 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.
Potential transformer.
5:1.

32. The purpose of a zig-zag transformer is to...
5:1.
100 turns.
Derive a neutral for grounding purposes.
At the source transformer.

33. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
2000 watts
Short-circuited after power has been removed.
Draw less current.

34. A solenoid coil is...
An electromagnet.
Squirrel-cage rotor.
5:1
Squirrel-cage induction motor.

35. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
H terminals.
Second-degree burn.
277 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

36. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The motor rotation is reversed.
The sum of the two capacitors.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Stator windings.

37. The secondary windings on a 10:1 step-down transformer will have a wire size...
Current changing constantly in magnitude and periodically in direction.
H terminals.
Larger than that found in the primary winding.
Cut around clothing that has adhered to the burned area.

38. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Tied together
277 volts.
2000 watts
60 cycles per second (60 Hertz).

39. Which of the following does a squirrel cage induction motor have?
Squirrel-cage induction motor.
The capacitors should be discharged.
150 turns.
Stator windings.

40. Compared to the secondary of a loaded - step-down transformer - the primary has...
Tied together
H terminals.
Lower current and higher voltage.
Continuous.

41. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Cut around clothing that has adhered to the burned area.
1 amp.
Check to make sure that the victim is not still in contact with the electricity.
Reverse any two-phase leads.

42. High voltage is used to transmit power over long distances...
5:1
Transformers.
Because less current flowing at high voltage causes less line loss per kilowatt.
Shunted and taped

43. Define alternating current...
Draw less current.
Current changing constantly in magnitude and periodically in direction.
75 turns.
It provides good speed control.

44. What is the danger when working around capacitors?
600 volts.
12 to 15 times a minute.
100 turns.
An electrical shock hazard may exist.

45. 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.
12 to 15 times a minute.
H terminals.
Squirrel-cage rotor.

46. The transformer used only to measure voltage is a...
Potential transformer.
No.6 AWG.
Hyperventilation.
Larger than that found in the primary winding.

47. The primary leads of a single-phase transformer should be connected to the...
Continuous.
H terminals.
100 volts.
5:1.

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

49. 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?
A step-up transformer.
Alternating current.
An electrical shock hazard may exist.
200 volts AC.

50. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Disconnect the frame-grounding conductor.
The capacitors should be discharged.
The motor rotation is reversed.