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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. All transformers step voltage up or down by...
Disconnect the frame-grounding conductor.
Second-degree burn.
Lower current and higher voltage.
Inductance.

2. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Inductance.
Check to make sure that the victim is not still in contact with the electricity.
2000 watts
Inductance.

3. A transformer has a primary voltage of 2 -400 volts and a secondary reading of 120 volts. If there are 1 -500 turns on the primary - how many turns are on the secondary?
Hyperventilation.
Electro-magnetism for their operation.
75 turns.
An electrical shock hazard may exist.

4. What steps up or steps down AC voltage?
Transformer
60 Hertz
5:1
The capacitors should be discharged.

5. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
7 -630 volts.
Capacitance.
60 cycles per second (60 Hertz).
12 to 15 times a minute.

6. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Continuous.
Allow for metering voltage and Current.
The capacitors should be discharged.

7. Operating coils - motors - transformers - relays and solenoids depend upon...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Larger than that found in the primary winding.
Clamp-on ammeter.
Electro-magnetism for their operation.

8. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
100 volts.
Zero amps.
Reverse any two-phase leads.
Cut around clothing that has adhered to the burned area.

9. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
75 turns.
No.6 AWG.
277 volts.
Current changing constantly in magnitude and periodically in direction.

10. 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.
Hyperventilation.
480 volts.
75 turns.

11. The property of an electric circuit that opposes any change in current is called...
Tied together
At the source transformer.
Inductance.
800 volts.

12. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
15 feet off the ground.
1 amp.
Isolation transformer.
It provides good speed control.

13. High voltage is used to transmit power over long distances...
The chest should rise or inflate.
The capacitors should be discharged.
Because less current flowing at high voltage causes less line loss per kilowatt.
They must be installed at least 7 feet above the ground.

14. A wound-rotor induction motor has all the following EXCEPT...
H terminals.
At least two phases
Inductance.
Squirrel-cage rotor.

15. Compared to the secondary of a loaded - step-down transformer - the primary has...
No.6 AWG.
Lower current and higher voltage
Current that changes constantly in magnitude and periodically in direction.
Derive a neutral for grounding purposes.

16. The standard frequency of alternating current used at a mine is...
75 turns.
60 Hertz
Transformers.
600 volts.

17. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
The current will read zero.
Alternating current.
Lower current and higher voltage.

18. The primary leads of a single-phase transformer should be connected to the...
The sum of the two capacitors.
H terminals.
75 turns.
100 turns.

19. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Shunted and taped
277 volts.
12 to 15 times a minute.
Larger than that found in the primary winding.

20. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
Squirrel-cage induction motor.
2000 watts
Disconnect the frame-grounding conductor.

21. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Alternating current.
60 Hertz
Grounded phase and ground fault devices were not operating.
An electrical shock hazard may exist.

22. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
An electromagnet.
Carotid pulse - which is located in the neck next to the Adam's apple.
Squirrel-cage rotor.
A step-up transformer.

23. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
5:1.
An electromagnet.
The capacitors should be discharged.
A step-up transformer.

24. What is a capacitor?
5:1.
Capacitance.
Draw less current.
A device used to store electrical energy.

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

26. 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.
Check to make sure that the victim is not still in contact with the electricity.
5:1
No.6 AWG.
Circuit Breaker.

27. Current that changes periodically in direction is...
Continuous.
Alternating current.
600 volts.
Zero amps.

28. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Disconnect the frame-grounding conductor.
277 volts.
Reverse any two-phase leads.

29. The property of an electrical circuit that opposes any change in voltage is called...
The chest should rise or inflate.
Capacitance.
3 -979 Volts.
150 turns.

30. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Derive a neutral for grounding purposes.
Disconnect the frame-grounding conductor.
H terminals.
Draw less current.

31. 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?
100 turns.
3 -979 Volts.
Squirrel-cage induction motor.
Reverse its rotation.

32. 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.
They should be made by the same manufacturer.
5:1
Transformer

33. Which of the following does a squirrel cage induction motor have?
Stator windings.
Full-load - three-phase voltage.
480 volts.
Derive a neutral for grounding purposes.

34. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Lower current and higher voltage.
15 feet off the ground.
600 volts.
No.6 AWG.

35. The main function of CT's and PT's on a main substation is to...
Nearly constant.
25 feet.
Allow for metering voltage and Current.
Draw less current.

36. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
It provides good speed control.
Two speeds
Squirrel-cage rotor.

37. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
The current will read zero.
Larger than that found in the primary winding.
Capacitance.

38. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
Electro-magnetism for their operation.
Check to make sure that the victim is not still in contact with the electricity.
Reverse any two-phase leads.

39. When not connected to a load - the secondary leads of a current transformer should be...
3 -979 Volts.
Hyperventilation.
Shunted and taped
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

40. The purpose of a zig-zag transformer is to...
Potential transformer.
Derive a neutral for grounding purposes.
2000 watts
100 turns.

41. The transformer used only to measure voltage is a...
Draw less current.
Potential transformer.
480 volts.
60 Hertz

42. A burn causing a blister is classified as a...
It provides good speed control.
Second-degree burn.
5:1.
25 feet.

43. A solenoid coil is...
Derive a neutral for grounding purposes.
At least two phases
An electromagnet.
It provides good speed control.

44. 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...
Continuous.
Draw less current.
100 turns.
60 cycles per second (60 Hertz).

45. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Clamp-on ammeter.
480 volts.
1 amp.
Potential transformer.

46. 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.
Two speeds
Current changing constantly in magnitude and periodically in direction.
H terminals.

47. Current in an AC circuit may be measured by...
The current will read zero.
A.C.
Clamp-on ammeter.
Grounded phase and ground fault devices were not operating.

48. The secondary windings on a 10:1 step-down transformer will have a wire size...
The capacitors should be discharged.
Capacitance.
Larger than that found in the primary winding.
200 volts AC.

49. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Disconnect the frame-grounding conductor.
Zero amps.
Short-circuited after power has been removed.
Draw less current.

50. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A step-up transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.
A grounding resistor.
5:1