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

2. The combined capacitance of two capacitors in parallel is...
Inductance.
Check to make sure that the victim is not still in contact with the electricity.
The sum of the two capacitors.
Zero amps.

3. AC voltage is raised or lowered by means of...
X.
Four times less than that of the secondary.
Transformers.
100 turns.

4. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
75 turns.
100 turns.
Because less current flowing at high voltage causes less line loss per kilowatt.
A grounding resistor.

5. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
They must be installed at least 7 feet above the ground.
600 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.

6. A control power transformer...
Alternating current.
60 cycles per second (60 Hertz).
Provides single-phase power to smaller loads such as lights - heaters - etc.
The current will read zero.

7. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
The motor rotation is reversed.
Clamp-on ammeter.
Draw less current.

8. 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...
60 Hertz
Because less current flowing at high voltage causes less line loss per kilowatt.
Tied together
2000 watts

9. 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 induction motor.
Cut around clothing that has adhered to the burned area.
75 turns.
Potential transformer.

10. What is the danger when working around capacitors?
At the source transformer.
An electrical shock hazard may exist.
Zero amps.
Inductance.

11. The purpose of a zig-zag transformer is to...
An electromagnet.
At the source transformer.
No.6 AWG.
Derive a neutral for grounding purposes.

12. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Reverse any two-phase leads.
They must be installed at least 7 feet above the ground.
The motor rotation is reversed.
Provides single-phase power to smaller loads such as lights - heaters - etc.

13. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Short-circuited after power has been removed.
100 turns.
Four times less than that of the secondary.
Clamp-on ammeter.

14. Current in an AC circuit may be measured by...
Potential transformer.
Clamp-on ammeter.
600 volts.
Circuit Breaker.

15. How should clothing be removed from a burn?
Isolation transformer.
Cut around clothing that has adhered to the burned area.
Grounded phase and ground fault devices were not operating.
At least two phases

16. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Alternating current.
The capacitors should be discharged.
A grounding resistor.

17. 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
A grounding resistor.
A device used to store electrical energy.
Transformers.

18. Not an acceptable method for the installations of surface transformers?
3 -979 Volts.
Full-load - three-phase voltage.
Zero amps.
They must be installed at least 7 feet above the ground.

19. Alternating current may be defined as...
277 volts.
Four times less than that of the secondary.
Current that changes constantly in magnitude and periodically in direction.
Clamp-on ammeter.

20. How do you change the direction of a 3-phase AC motor?
Because less current flowing at high voltage causes less line loss per kilowatt.
Draw less current.
Reverse any two-phase leads.
Hyperventilation.

21. 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?
Shunted and taped
An electromagnet.
Because less current flowing at high voltage causes less line loss per kilowatt.
100 turns.

22. Not a symptom of electrical shock?.
Reverse any two-phase leads.
Hyperventilation.
Reverse its rotation.
At least two phases

23. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Capacitance.
Draw less current.
A.C.

24. Compared to the secondary of a loaded - step-down transformer - the primary has...
Potential transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.
1 amp.
Lower current and higher voltage.

25. 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...
An electrical shock hazard may exist.
12 to 15 times a minute.
Lower current and higher voltage.
Draw less current.

26. If any two-phase wires are reversed on a three-phase motor - the motor will...
Cut around clothing that has adhered to the burned area.
Squirrel-cage rotor.
Reverse its rotation.
Transformer

27. What steps up or steps down AC voltage?
Allow for metering voltage and Current.
The motor rotation is reversed.
60 cycles per second (60 Hertz).
Transformer

28. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
480 volts.
They must be installed at least 7 feet above the ground.
60 cycles per second (60 Hertz).

29. The standard frequency of alternating current used at a mine is...
60 cycles per second (60 Hertz).
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
60 Hertz
Disconnect the frame-grounding conductor.

30. 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.
5:1.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Nearly constant.
Lower current and higher voltage.

31. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
60 cycles per second (60 Hertz).
At the source transformer.
Potential transformer.

32. When not connected to a load - the secondary leads of a current transformer should be...
60 cycles per second (60 Hertz).
Draw less current.
Shunted and taped
A.C.

33. Not true about AC power?
Nearly constant.
It provides good speed control.
Larger than that found in the primary winding.
Check to make sure that the victim is not still in contact with the electricity.

34. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
A step-up transformer.
100 volts.
At the source transformer.

35. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Stator windings.
2000 watts
The chest should rise or inflate.
A step-up transformer.

36. 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.
15 feet off the ground.
Two speeds

37. What should the duty rating of a grounding resistor be?
Inductance.
A.C.
25 feet.
Continuous.

38. The size of a transformer is measured in...
Hyperventilation.
Two speeds
Provides single-phase power to smaller loads such as lights - heaters - etc.
Kilovolt ampere (KVA).

39. Current that changes periodically in direction is...
Full-load - three-phase voltage.
Alternating current.
75 turns.
12 to 15 times a minute.

40. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Clamp-on ammeter.
Reverse any two-phase leads.
Full-load - three-phase voltage.
1 amp.

41. 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?
Squirrel-cage rotor.
150 turns.
They should be made by the same manufacturer.
The sum of the two capacitors.

42. All transformers step voltage up or down by...
Disconnect the frame-grounding conductor.
At least two phases
Inductance.
1 amp.

43. 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 Hertz
They should be made by the same manufacturer.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

44. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Cut around clothing that has adhered to the burned area.
Reverse any two-phase leads.
Allow for metering voltage and Current.
X.

45. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
It provides good speed control.
150 turns.
Tied together

46. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
60 Hertz
Current changing constantly in magnitude and periodically in direction.
It provides good speed control.

47. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Disconnect the frame-grounding conductor.

48. 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...
Draw less current.
A device used to store electrical energy.
Kilovolt ampere (KVA).
Reverse any two-phase leads.

49. Three-phase AC underground cables must be provided with overcurrent protection using a...
Current changing constantly in magnitude and periodically in direction.
Circuit Breaker.
Squirrel-cage induction motor.
Stator windings.

50. 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...
Grounded phase and ground fault devices were not operating.
Potential transformer.
100 volts.
Reverse its rotation.