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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. 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?
15 feet off the ground.
150 turns.
The chest should rise or inflate.
3 -979 Volts.

2. What type motor is a wound-rotor induction motor?
A.C.
277 volts.
Squirrel-cage induction motor.
150 turns.

3. 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.
100 turns.
5:1
A device used to store electrical energy.
Because less current flowing at high voltage causes less line loss per kilowatt.

4. 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...
Second-degree burn.
1 amp.
Short-circuited after power has been removed.
Draw less current.

5. Which of the following does a squirrel cage induction motor have?
Tied together
The capacitors should be discharged.
Stator windings.
2000 watts

6. What is the danger when working around capacitors?
Derive a neutral for grounding purposes.
An electrical shock hazard may exist.
277 volts.
A grounding resistor.

7. What is the first step to be followed in aiding a victim of electrical shock?
Check to make sure that the victim is not still in contact with the electricity.
Current changing constantly in magnitude and periodically in direction.
Because less current flowing at high voltage causes less line loss per kilowatt.
Transformers.

8. The transformer used only to measure voltage is a...
Potential transformer.
A.C.
Lower current and higher voltage.
Squirrel-cage rotor.

9. 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?
Squirrel-cage induction motor.
Grounded phase and ground fault devices were not operating.
Hyperventilation.
800 volts.

10. Current transformers - or CT's - are used to...
15 feet off the ground.
Zero amps.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Disconnect the frame-grounding conductor.

11. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Four times less than that of the secondary.
15 feet off the ground.
5:1.
X.

12. A wound-rotor induction motor has all the following EXCEPT...
An electrical shock hazard may exist.
Squirrel-cage rotor.
3 -979 Volts.
Four times less than that of the secondary.

13. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Allow for metering voltage and Current.
Stator windings.
Reverse its rotation.
2000 watts

14. To protect against over-current in a three-phase circuit over-current protection must be provided for...
480 volts.
5:1
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
At least two phases

15. The combined capacitance of two capacitors in parallel is...
Disconnect the frame-grounding conductor.
Alternating current.
Draw less current.
The sum of the two capacitors.

16. The speed of an alternating current - squirrel-cage induction motor is...
Second-degree burn.
Carotid pulse - which is located in the neck next to the Adam's apple.
3 -979 Volts.
Nearly constant.

17. AC voltage is raised or lowered by means of...
Grounded phase and ground fault devices were not operating.
Clamp-on ammeter.
Because less current flowing at high voltage causes less line loss per kilowatt.
Transformers.

18. What should the duty rating of a grounding resistor be?
Carotid pulse - which is located in the neck next to the Adam's apple.
No.6 AWG.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Continuous.

19. Not true about AC power?
It provides good speed control.
3 -979 Volts.
Potential transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

20. A transformer with a 1:1 ratio is usually a (an)...
The motor rotation is reversed.
Isolation transformer.
Shunted and taped
They should be made by the same manufacturer.

21. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The sum of the two capacitors.
Grounded phase and ground fault devices were not operating.
60 cycles per second (60 Hertz).
The motor rotation is reversed.

22. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Clamp-on ammeter.
Check to make sure that the victim is not still in contact with the electricity.
Four times less than that of the secondary.
Squirrel-cage rotor.

23. Current that changes periodically in direction is...
Alternating current.
An electrical shock hazard may exist.
Larger than that found in the primary winding.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

24. 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?
277 volts.
150 turns.
The motor rotation is reversed.
Draw less current.

25. Not a symptom of electrical shock?.
Cut around clothing that has adhered to the burned area.
A grounding resistor.
Tied together
Hyperventilation.

26. The main function of CT's and PT's on a main substation is to...
100 turns.
Draw less current.
Allow for metering voltage and Current.
A grounding resistor.

27. Operating coils - motors - transformers - relays and solenoids depend upon...
Current that changes constantly in magnitude and periodically in direction.
75 turns.
Squirrel-cage rotor.
Electro-magnetism for their operation.

28. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Disconnect the frame-grounding conductor.
A grounding resistor.
Two speeds
60 cycles per second (60 Hertz).

29. Define alternating current...
At least two phases
Current changing constantly in magnitude and periodically in direction.
A device used to store electrical energy.
1 amp.

30. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Potential transformer.
Squirrel-cage rotor.
Kilovolt ampere (KVA).

31. The primary leads of a single-phase transformer should be connected to the...
600 volts.
H terminals.
Reverse its rotation.
The motor rotation is reversed.

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

33. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
A grounding resistor.
Capacitance.
15 feet off the ground.
Potential transformer.

34. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
200 volts AC.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Transformers.
25 feet.

35. 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...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Lower current and higher voltage.
Draw less current.
60 Hertz

36. Where should grounding resistors be located?
150 turns.
At the source transformer.
Disconnect the frame-grounding conductor.
They must be installed at least 7 feet above the ground.

37. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
Two speeds
200 volts AC.
The motor rotation is reversed.

38. The size of a transformer is measured in...
Kilovolt ampere (KVA).
Circuit Breaker.
Electro-magnetism for their operation.
Draw less current.

39. What is a capacitor?
It provides good speed control.
Draw less current.
A device used to store electrical energy.
Cut around clothing that has adhered to the burned area.

40. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
5:1
600 volts.
Four times less than that of the secondary.

41. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
2000 watts
Lower current and higher voltage
Electro-magnetism for their operation.
1 amp.

42. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
The current will read zero.
Zero amps.
Reverse any two-phase leads.

43. How should clothing be removed from a burn?
Hyperventilation.
277 volts.
Cut around clothing that has adhered to the burned area.
Continuous.

44. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Squirrel-cage rotor.
Stator windings.
Squirrel-cage induction motor.

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...
Current changing constantly in magnitude and periodically in direction.
Clamp-on ammeter.
The capacitors should be discharged.
Tied together

46. High voltage is used to transmit power over long distances...
Two speeds
Provides single-phase power to smaller loads such as lights - heaters - etc.
Electro-magnetism for their operation.
Because less current flowing at high voltage causes less line loss per kilowatt.

47. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
A.C.
25 feet.
Continuous.
A grounding resistor.

48. The primary function of a power transformer is to provide...
1 amp.
Full-load - three-phase voltage.
The sum of the two capacitors.
H terminals.

49. 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.
H terminals.
Cut around clothing that has adhered to the burned area.
800 volts.

50. 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.
Stator windings.
An electromagnet.
A step-up transformer.