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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. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
The motor rotation is reversed.
Larger than that found in the primary winding.
A grounding resistor.

2. 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?
150 turns.
A step-up transformer.
75 turns.
Inductance.

3. The primary function of a power transformer is to provide...
X.
Clamp-on ammeter.
Full-load - three-phase voltage.
3 -979 Volts.

4. At what rate should mouth-to-mouth resuscitation be applied?
200 volts AC.
12 to 15 times a minute.
Hyperventilation.
Potential transformer.

5. A control power transformer...
It provides good speed control.
Provides single-phase power to smaller loads such as lights - heaters - etc.
15 feet off the ground.
Current changing constantly in magnitude and periodically in direction.

6. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Alternating current.
Disconnect the frame-grounding conductor.
Electro-magnetism for their operation.
Tied together

7. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Check to make sure that the victim is not still in contact with the electricity.
No.6 AWG.
They should be made by the same manufacturer.
Derive a neutral for grounding purposes.

8. 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?
An electromagnet.
200 volts AC.
800 volts.
Alternating current.

9. The combined capacitance of two capacitors in parallel is...
Zero amps.
12 to 15 times a minute.
Inductance.
The sum of the two capacitors.

10. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Tied together
Larger than that found in the primary winding.
A grounding resistor.
Hyperventilation.

11. 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?
Because less current flowing at high voltage causes less line loss per kilowatt.
X.
75 turns.
3 -979 Volts.

12. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Isolation transformer.
Squirrel-cage induction motor.
Provides single-phase power to smaller loads such as lights - heaters - etc.
1 amp.

13. What should the duty rating of a grounding resistor be?
Isolation transformer.
7 -630 volts.
Continuous.
The sum of the two capacitors.

14. AC voltage is raised or lowered by means of...
Transformers.
They must be installed at least 7 feet above the ground.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Shunted and taped

15. What is a capacitor?
2000 watts
480 volts.
800 volts.
A device used to store electrical energy.

16. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Inductance.
The chest should rise or inflate.
Kilovolt ampere (KVA).
800 volts.

17. The main function of CT's and PT's on a main substation is to...
A.C.
Allow for metering voltage and Current.
12 to 15 times a minute.
Inductance.

18. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Nearly constant.
Hyperventilation.
Short-circuited after power has been removed.
Larger than that found in the primary winding.

19. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Two speeds
1 amp.
Reverse any two-phase leads.
277 volts.

20. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Kilovolt ampere (KVA).
Derive a neutral for grounding purposes.
Provides single-phase power to smaller loads such as lights - heaters - etc.

21. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
H terminals.
No.6 AWG.
Lower current and higher voltage
Second-degree burn.

22. The secondary windings on a 10:1 step-down transformer will have a wire size...
Inductance.
277 volts.
Larger than that found in the primary winding.
5:1.

23. 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...
100 volts.
Inductance.
Tied together
Capacitance.

24. What is the danger when working around capacitors?
Carotid pulse - which is located in the neck next to the Adam's apple.
An electrical shock hazard may exist.
Draw less current.
480 volts.

25. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
150 turns.
Hyperventilation.
Transformers.

26. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
Current changing constantly in magnitude and periodically in direction.
12 to 15 times a minute.
Disconnect the frame-grounding conductor.

27. 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.
Full-load - three-phase voltage.
5:1.
The chest should rise or inflate.
Potential transformer.

28. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The current will read zero.
600 volts.
75 turns.
The motor rotation is reversed.

29. 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.
H terminals.
5:1
Carotid pulse - which is located in the neck next to the Adam's apple.

30. The size of a transformer is measured in...
At the source transformer.
Inductance.
Kilovolt ampere (KVA).
1 amp.

31. The purpose of a zig-zag transformer is to...
Carotid pulse - which is located in the neck next to the Adam's apple.
150 turns.
5:1
Derive a neutral for grounding purposes.

32. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
The sum of the two capacitors.
25 feet.
Current that changes constantly in magnitude and periodically in direction.

33. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
800 volts.
Continuous.
X.
Derive a neutral for grounding purposes.

34. 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...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
100 volts.
Electro-magnetism for their operation.
5:1

35. The property of an electrical circuit that opposes any change in voltage is called...
Shunted and taped
Kilovolt ampere (KVA).
Capacitance.
75 turns.

36. What steps up or steps down AC voltage?
Zero amps.
Transformer
1 amp.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

37. The speed of an alternating current - squirrel-cage induction motor is...
No.6 AWG.
150 turns.
Nearly constant.
They should be made by the same manufacturer.

38. 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.
The chest should rise or inflate.
60 cycles per second (60 Hertz).
A step-up transformer.

39. 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...
15 feet off the ground.
Clamp-on ammeter.
At least two phases
Draw less current.

40. Not an acceptable method for the installations of surface transformers?
Isolation transformer.
They must be installed at least 7 feet above the ground.
Carotid pulse - which is located in the neck next to the Adam's apple.
Second-degree burn.

41. Compared to the secondary of a loaded - step-down transformer - the primary has...
Stator windings.
100 turns.
Potential transformer.
Lower current and higher voltage.

42. A burn causing a blister is classified as a...
A step-up transformer.
A device used to store electrical energy.
Second-degree burn.
The current will read zero.

43. What type motor is a wound-rotor induction motor?
Alternating current.
Tied together
A.C.
12 to 15 times a minute.

44. Current transformers - or CT's - are used to...
7 -630 volts.
They must be installed at least 7 feet above the ground.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Electro-magnetism for their operation.

45. Which of the following does a squirrel cage induction motor have?
Stator windings.
5:1
Kilovolt ampere (KVA).
Because less current flowing at high voltage causes less line loss per kilowatt.

46. The transformer used only to measure voltage is a...
The sum of the two capacitors.
They must be installed at least 7 feet above the ground.
It provides good speed control.
Potential transformer.

47. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Two speeds
Zero amps.
Current that changes constantly in magnitude and periodically in direction.
Hyperventilation.

48. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
60 Hertz
The chest should rise or inflate.
An electromagnet.

49. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
100 turns.
Four times less than that of the secondary.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Hyperventilation.

50. What is the first step to be followed in aiding a victim of electrical shock?
Cut around clothing that has adhered to the burned area.
Check to make sure that the victim is not still in contact with the electricity.
Second-degree burn.
X.