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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 any two-phase wires are reversed on a three-phase motor - the motor will...
Disconnect the frame-grounding conductor.
Derive a neutral for grounding purposes.
Reverse its rotation.
12 to 15 times a minute.

2. The standard frequency of power supplied by the power company is...
Carotid pulse - which is located in the neck next to the Adam's apple.
It provides good speed control.
60 cycles per second (60 Hertz).
The current will read zero.

3. Current in an AC circuit may be measured by...
Draw less current.
Stator windings.
Allow for metering voltage and Current.
Clamp-on ammeter.

4. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
An electromagnet.
Zero amps.
At the source transformer.

5. 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?
12 to 15 times a minute.
The sum of the two capacitors.
800 volts.
Clamp-on ammeter.

6. What type motor is a wound-rotor induction motor?
60 cycles per second (60 Hertz).
7 -630 volts.
A.C.
Cut around clothing that has adhered to the burned area.

7. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
12 to 15 times a minute.
150 turns.
Larger than that found in the primary winding.

8. AC voltage is raised or lowered by means of...
Short-circuited after power has been removed.
Reverse any two-phase leads.
Transformers.
A grounding resistor.

9. 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?
Carotid pulse - which is located in the neck next to the Adam's apple.
5:1
600 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.

10. What is the first step to be followed in aiding a victim of electrical shock?
Transformer
Check to make sure that the victim is not still in contact with the electricity.
5:1.
200 volts AC.

11. The property of an electrical circuit that opposes any change in voltage is called...
Four times less than that of the secondary.
The capacitors should be discharged.
12 to 15 times a minute.
Capacitance.

12. Current transformers - or CT's - are used to...
Alternating current.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
At the source transformer.
25 feet.

13. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Tied together
277 volts.
They should be made by the same manufacturer.
Lower current and higher voltage.

14. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Squirrel-cage induction motor.
Short-circuited after power has been removed.
Current changing constantly in magnitude and periodically in direction.
60 cycles per second (60 Hertz).

15. Operating coils - motors - transformers - relays and solenoids depend upon...
H terminals.
Grounded phase and ground fault devices were not operating.
800 volts.
Electro-magnetism for their operation.

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

17. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Carotid pulse - which is located in the neck next to the Adam's apple.
100 turns.
Current that changes constantly in magnitude and periodically in direction.

18. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
Because less current flowing at high voltage causes less line loss per kilowatt.
Two speeds
Provides single-phase power to smaller loads such as lights - heaters - etc.

19. A burn causing a blister is classified as a...
Second-degree burn.
The current will read zero.
Draw less current.
1 amp.

20. A wound-rotor induction motor has all the following EXCEPT...
Lower current and higher voltage.
Squirrel-cage rotor.
Check to make sure that the victim is not still in contact with the electricity.
A grounding resistor.

21. What is the danger when working around capacitors?
An electrical shock hazard may exist.
2000 watts
Circuit Breaker.
75 turns.

22. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Squirrel-cage rotor.
Disconnect the frame-grounding conductor.
Draw less current.
Cut around clothing that has adhered to the burned area.

23. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Potential transformer.
Alternating current.
480 volts.

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?
277 volts.
3 -979 Volts.
Draw less current.
Disconnect the frame-grounding conductor.

25. All transformers step voltage up or down by...
A step-up transformer.
H terminals.
Inductance.
Check to make sure that the victim is not still in contact with the electricity.

26. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
A device used to store electrical energy.
7 -630 volts.
An electromagnet.

27. 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...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Draw less current.
Check to make sure that the victim is not still in contact with the electricity.
Hyperventilation.

28. 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?
An electromagnet.
75 turns.
277 volts.
Grounded phase and ground fault devices were not operating.

29. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
A.C.
Because less current flowing at high voltage causes less line loss per kilowatt.
7 -630 volts.

30. The purpose of a zig-zag transformer is to...
The current will read zero.
The chest should rise or inflate.
Hyperventilation.
Derive a neutral for grounding purposes.

31. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
They must be installed at least 7 feet above the ground.
Grounded phase and ground fault devices were not operating.
Check to make sure that the victim is not still in contact with the electricity.
Squirrel-cage induction motor.

32. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The current will read zero.
277 volts.
Hyperventilation.
Zero amps.

33. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Electro-magnetism for their operation.
480 volts.
Transformer
75 turns.

34. 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.
Allow for metering voltage and Current.
5:1
Squirrel-cage rotor.
Current changing constantly in magnitude and periodically in direction.

35. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Nearly constant.
7 -630 volts.
25 feet.
Tied together

36. Not a symptom of electrical shock?.
Hyperventilation.
800 volts.
Second-degree burn.
Short-circuited after power has been removed.

37. A transformer with a 1:1 ratio is usually a (an)...
25 feet.
Alternating current.
Isolation transformer.
Reverse any two-phase leads.

38. Three-phase AC underground cables must be provided with overcurrent protection using a...
An electromagnet.
Because less current flowing at high voltage causes less line loss per kilowatt.
Isolation transformer.
Circuit Breaker.

39. 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...
They should be made by the same manufacturer.
Tied together
Cut around clothing that has adhered to the burned area.
Disconnect the frame-grounding conductor.

40. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
Current that changes constantly in magnitude and periodically in direction.
15 feet off the ground.
12 to 15 times a minute.

41. 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
Larger than that found in the primary winding.
An electromagnet.

42. 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.
Circuit Breaker.
75 turns.
Squirrel-cage rotor.

43. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Clamp-on ammeter.
Second-degree burn.
A grounding resistor.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

44. The main function of CT's and PT's on a main substation is to...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
75 turns.
Allow for metering voltage and Current.
Electro-magnetism for their operation.

45. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Potential transformer.
1 amp.
15 feet off the ground.
Because less current flowing at high voltage causes less line loss per kilowatt.

46. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Reverse any two-phase leads.
Disconnect the frame-grounding conductor.
Cut around clothing that has adhered to the burned area.
Two speeds

47. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
Derive a neutral for grounding purposes.
Clamp-on ammeter.
Allow for metering voltage and Current.

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

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

50. Which of the following does a squirrel cage induction motor have?
The chest should rise or inflate.
5:1
Stator windings.
They should be made by the same manufacturer.