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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. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Isolation transformer.
15 feet off the ground.
Nearly constant.
At least two phases

2. Which of the following does a squirrel cage induction motor have?
Stator windings.
Draw less current.
They should be made by the same manufacturer.
150 turns.

3. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
5:1
Short-circuited after power has been removed.
At least two phases
60 Hertz

4. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A grounding resistor.
It provides good speed control.
Electro-magnetism for their operation.
Isolation transformer.

5. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Isolation transformer.
75 turns.
No.6 AWG.
150 turns.

6. 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.
5:1.
A step-up transformer.
Current that changes constantly in magnitude and periodically in direction.

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

8. 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?
5:1.
Shunted and taped
800 volts.
At the source transformer.

9. Three-phase AC underground cables must be provided with overcurrent protection using a...
Reverse any two-phase leads.
Transformers.
Tied together
Circuit Breaker.

10. The secondary windings on a 10:1 step-down transformer will have a wire size...
Electro-magnetism for their operation.
Larger than that found in the primary winding.
Disconnect the frame-grounding conductor.
The motor rotation is reversed.

11. Not a symptom of electrical shock?.
Derive a neutral for grounding purposes.
Check to make sure that the victim is not still in contact with the electricity.
Hyperventilation.
Current that changes constantly in magnitude and periodically in direction.

12. 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
Squirrel-cage rotor.
600 volts.
Circuit Breaker.

13. The size of a transformer is measured in...
Lower current and higher voltage
A device used to store electrical energy.
Kilovolt ampere (KVA).
Disconnect the frame-grounding conductor.

14. 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?
60 Hertz
Transformers.
They should be made by the same manufacturer.
600 volts.

15. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
75 turns.
No.6 AWG.
480 volts.
Zero amps.

16. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Hyperventilation.
Second-degree burn.
Draw less current.
The chest should rise or inflate.

17. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
The capacitors should be discharged.
5:1.
A step-up transformer.
Grounded phase and ground fault devices were not operating.

18. 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...
150 turns.
100 volts.
Inductance.
480 volts.

19. When not connected to a load - the secondary leads of a current transformer should be...
Transformers.
Shunted and taped
Isolation transformer.
A device used to store electrical energy.

20. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Circuit Breaker.
Disconnect the frame-grounding conductor.
25 feet.
Potential transformer.

21. The speed of an alternating current - squirrel-cage induction motor is...
An electromagnet.
X.
Nearly constant.
5:1

22. Not true about AC power?
Inductance.
Four times less than that of the secondary.
277 volts.
It provides good speed control.

23. The transformer used only to measure voltage is a...
Draw less current.
60 cycles per second (60 Hertz).
75 turns.
Potential transformer.

24. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
Check to make sure that the victim is not still in contact with the electricity.
Draw less current.
Because less current flowing at high voltage causes less line loss per kilowatt.

25. 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?
100 turns.
75 turns.
Kilovolt ampere (KVA).
Zero amps.

26. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
The sum of the two capacitors.
Two speeds
150 turns.
7 -630 volts.

27. 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...
No.6 AWG.
5:1.
Tied together
The current will read zero.

28. Current that changes periodically in direction is...
7 -630 volts.
480 volts.
Current that changes constantly in magnitude and periodically in direction.
Alternating current.

29. 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.
Electro-magnetism for their operation.
75 turns.
5:1.

30. What steps up or steps down AC voltage?
Transformer
Draw less current.
An electrical shock hazard may exist.
480 volts.

31. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Short-circuited after power has been removed.
Because less current flowing at high voltage causes less line loss per kilowatt.
Four times less than that of the secondary.
A step-up transformer.

32. A burn causing a blister is classified as a...
A device used to store electrical energy.
Second-degree burn.
Allow for metering voltage and Current.
200 volts AC.

33. A control power transformer...
Inductance.
2000 watts
Provides single-phase power to smaller loads such as lights - heaters - etc.
3 -979 Volts.

34. What is the danger when working around capacitors?
A.C.
An electrical shock hazard may exist.
Check to make sure that the victim is not still in contact with the electricity.
Isolation transformer.

35. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Inductance.
Two speeds
Provides single-phase power to smaller loads such as lights - heaters - etc.
Because less current flowing at high voltage causes less line loss per kilowatt.

36. A solenoid coil is...
Transformer
An electromagnet.
An electrical shock hazard may exist.
2000 watts

37. Define alternating current...
Reverse its rotation.
Lower current and higher voltage.
Current changing constantly in magnitude and periodically in direction.
Kilovolt ampere (KVA).

38. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Circuit Breaker.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

39. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
Two speeds
100 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.

40. Current transformers - or CT's - are used to...
480 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Tied together
Grounded phase and ground fault devices were not operating.

41. 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?
H terminals.
Current that changes constantly in magnitude and periodically in direction.
The chest should rise or inflate.
200 volts AC.

42. The combined capacitance of two capacitors in parallel is...
At least two phases
No.6 AWG.
The sum of the two capacitors.
600 volts.

43. What is a capacitor?
A device used to store electrical energy.
2000 watts
600 volts.
1 amp.

44. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Draw less current.
Current changing constantly in magnitude and periodically in direction.
15 feet off the ground.
2000 watts

45. 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...
Larger than that found in the primary winding.
Transformers.
Draw less current.
Inductance.

46. A wound-rotor induction motor has all the following EXCEPT...
1 amp.
Circuit Breaker.
Squirrel-cage rotor.
100 volts.

47. 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?
Lower current and higher voltage
Circuit Breaker.
150 turns.
Check to make sure that the victim is not still in contact with the electricity.

48. The property of an electric circuit that opposes any change in current is called...
An electrical shock hazard may exist.
Inductance.
At the source transformer.
Tied together

49. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
1 amp.
Full-load - three-phase voltage.
3 -979 Volts.
They should be made by the same manufacturer.

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