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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. Current transformers - or CT's - are used to...
800 volts.
Cut around clothing that has adhered to the burned area.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
It provides good speed control.

2. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Zero amps.
Reverse any two-phase leads.
7 -630 volts.
277 volts.

3. High voltage is used to transmit power over long distances...
Hyperventilation.
Because less current flowing at high voltage causes less line loss per kilowatt.
Squirrel-cage rotor.
600 volts.

4. AC voltage is raised or lowered by means of...
Transformers.
Circuit Breaker.
Isolation transformer.
Current that changes constantly in magnitude and periodically in direction.

5. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
H terminals.
Alternating current.
Squirrel-cage rotor.
A grounding resistor.

6. The main function of CT's and PT's on a main substation is to...
Shunted and taped
5:1.
Reverse its rotation.
Allow for metering voltage and Current.

7. Current that changes periodically in direction is...
Alternating current.
Four times less than that of the secondary.
At the source transformer.
The capacitors should be discharged.

8. Current in an AC circuit may be measured by...
The capacitors should be discharged.
Clamp-on ammeter.
5:1.
15 feet off the ground.

9. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Hyperventilation.
The chest should rise or inflate.
Stator windings.
Nearly constant.

10. 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...
A grounding resistor.
The chest should rise or inflate.
Draw less current.
Current changing constantly in magnitude and periodically in direction.

11. 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?
2000 watts
Nearly constant.
100 turns.
The motor rotation is reversed.

12. What steps up or steps down AC voltage?
Shunted and taped
At the source transformer.
Check to make sure that the victim is not still in contact with the electricity.
Transformer

13. The standard frequency of alternating current used at a mine is...
Kilovolt ampere (KVA).
150 turns.
60 cycles per second (60 Hertz).
60 Hertz

14. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
Grounded phase and ground fault devices were not operating.
800 volts.
12 to 15 times a minute.

15. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
1 amp.
Allow for metering voltage and Current.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

16. The transformer used only to measure voltage is a...
Squirrel-cage induction motor.
150 turns.
Potential transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.

17. Three-phase AC underground cables must be provided with overcurrent protection using a...
75 turns.
Draw less current.
Circuit Breaker.
Cut around clothing that has adhered to the burned area.

18. A control power transformer...
At least two phases
Clamp-on ammeter.
Current that changes constantly in magnitude and periodically in direction.
Provides single-phase power to smaller loads such as lights - heaters - etc.

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

20. The standard frequency of power supplied by the power company is...
1 amp.
The motor rotation is reversed.
5:1
60 cycles per second (60 Hertz).

21. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
A.C.
12 to 15 times a minute.
X.
At least two phases

22. If any two-phase wires are reversed on a three-phase motor - the motor will...
Because less current flowing at high voltage causes less line loss per kilowatt.
Reverse its rotation.
Lower current and higher voltage
The sum of the two capacitors.

23. The secondary windings on a 10:1 step-down transformer will have a wire size...
No.6 AWG.
A device used to store electrical energy.
Larger than that found in the primary winding.
X.

24. Compared to the secondary of a loaded - step-down transformer - the primary has...
Full-load - three-phase voltage.
Lower current and higher voltage
5:1
Derive a neutral for grounding purposes.

25. Not a symptom of electrical shock?.
Isolation transformer.
Hyperventilation.
Reverse its rotation.
75 turns.

26. 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
Alternating current.
150 turns.
277 volts.

27. At what rate should mouth-to-mouth resuscitation be applied?
75 turns.
They should be made by the same manufacturer.
Because less current flowing at high voltage causes less line loss per kilowatt.
12 to 15 times a minute.

28. The property of an electric circuit that opposes any change in current is called...
Inductance.
75 turns.
Second-degree burn.
Reverse any two-phase leads.

29. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
12 to 15 times a minute.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
480 volts.

30. Where should grounding resistors be located?
5:1
Stator windings.
Cut around clothing that has adhered to the burned area.
At the source transformer.

31. What type motor is a wound-rotor induction motor?
A.C.
5:1.
An electrical shock hazard may exist.
Clamp-on ammeter.

32. All transformers step voltage up or down by...
Check to make sure that the victim is not still in contact with the electricity.
Grounded phase and ground fault devices were not operating.
200 volts AC.
Inductance.

33. 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...
Tied together
60 Hertz
The capacitors should be discharged.
Lower current and higher voltage

34. The primary leads of a single-phase transformer should be connected to the...
The chest should rise or inflate.
H terminals.
150 turns.
Stator windings.

35. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
12 to 15 times a minute.
Current that changes constantly in magnitude and periodically in direction.
Check to make sure that the victim is not still in contact with the electricity.
Short-circuited after power has been removed.

36. 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.
Capacitance.
1 amp.
5:1
An electrical shock hazard may exist.

37. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
They should be made by the same manufacturer.
200 volts AC.
Reverse its rotation.
Derive a neutral for grounding purposes.

38. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
60 cycles per second (60 Hertz).
They must be installed at least 7 feet above the ground.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Cut around clothing that has adhered to the burned area.

39. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
5:1.
Reverse its rotation.
1 amp.
Stator windings.

40. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
H terminals.
It provides good speed control.
Reverse any two-phase leads.

41. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Squirrel-cage rotor.
Clamp-on ammeter.
The motor rotation is reversed.
Hyperventilation.

42. The size of a transformer is measured in...
Kilovolt ampere (KVA).
Transformers.
They must be installed at least 7 feet above the ground.
It provides good speed control.

43. How do you change the direction of a 3-phase AC motor?
Inductance.
100 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Reverse any two-phase leads.

44. What should the duty rating of a grounding resistor be?
Continuous.
3 -979 Volts.
Tied together
Cut around clothing that has adhered to the burned area.

45. Not an acceptable method for the installations of surface transformers?
200 volts AC.
They must be installed at least 7 feet above the ground.
Transformers.
15 feet off the ground.

46. What is a capacitor?
7 -630 volts.
A device used to store electrical energy.
Current that changes constantly in magnitude and periodically in direction.
25 feet.

47. A wound-rotor induction motor has all the following EXCEPT...
Lower current and higher voltage.
Lower current and higher voltage
The current will read zero.
Squirrel-cage rotor.

48. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
Carotid pulse - which is located in the neck next to the Adam's apple.
Larger than that found in the primary winding.
Zero amps.

49. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
An electromagnet.
Isolation transformer.
Shunted and taped
Grounded phase and ground fault devices were not operating.

50. A solenoid coil is...
Inductance.
A grounding resistor.
An electromagnet.
Check to make sure that the victim is not still in contact with the electricity.