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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. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
It provides good speed control.
277 volts.
Nearly constant.

2. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The motor rotation is reversed.
X.
5:1
An electromagnet.

3. What should the duty rating of a grounding resistor be?
Squirrel-cage rotor.
3 -979 Volts.
200 volts AC.
Continuous.

4. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Short-circuited after power has been removed.
They should be made by the same manufacturer.
Reverse its rotation.
Nearly constant.

5. 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?
X.
The motor rotation is reversed.
H terminals.
3 -979 Volts.

6. Where should grounding resistors be located?
A.C.
Inductance.
At the source transformer.
150 turns.

7. 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...
100 turns.
Four times less than that of the secondary.
An electrical shock hazard may exist.
Draw less current.

8. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
Two speeds
Four times less than that of the secondary.
60 cycles per second (60 Hertz).

9. 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.
Alternating current.
2000 watts
X.

10. The primary leads of a single-phase transformer should be connected to the...
Transformers.
Circuit Breaker.
H terminals.
277 volts.

11. The combined capacitance of two capacitors in parallel is...
1 amp.
Short-circuited after power has been removed.
The sum of the two capacitors.
Continuous.

12. The standard frequency of power supplied by the power company is...
It provides good speed control.
60 cycles per second (60 Hertz).
Allow for metering voltage and Current.
A step-up transformer.

13. AC voltage is raised or lowered by means of...
Inductance.
Transformers.
Capacitance.
Provides single-phase power to smaller loads such as lights - heaters - etc.

14. Current transformers - or CT's - are used to...
Provides single-phase power to smaller loads such as lights - heaters - etc.
A.C.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
200 volts AC.

15. 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
Full-load - three-phase voltage.
Transformer
200 volts AC.

16. High voltage is used to transmit power over long distances...
Lower current and higher voltage.
Tied together
Because less current flowing at high voltage causes less line loss per kilowatt.
Continuous.

17. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
3 -979 Volts.
A grounding resistor.
Second-degree burn.

18. 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...
Potential transformer.
Cut around clothing that has adhered to the burned area.
600 volts.
Tied together

19. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
The capacitors should be discharged.
25 feet.
1 amp.
480 volts.

20. A control power transformer...
100 volts.
Electro-magnetism for their operation.
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.

21. What is the danger when working around capacitors?
An electrical shock hazard may exist.
15 feet off the ground.
Hyperventilation.
Short-circuited after power has been removed.

22. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Short-circuited after power has been removed.
Inductance.
Squirrel-cage induction motor.
Lower current and higher voltage.

23. 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.
Kilovolt ampere (KVA).
1 amp.
Current changing constantly in magnitude and periodically in direction.
5:1.

24. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Clamp-on ammeter.
Alternating current.
Shunted and taped

25. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
A grounding resistor.
Zero amps.
Larger than that found in the primary winding.
15 feet off the ground.

26. The secondary windings on a 10:1 step-down transformer will have a wire size...
25 feet.
They should be made by the same manufacturer.
Larger than that found in the primary winding.
1 amp.

27. 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.
Nearly constant.
Potential transformer.

28. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Inductance.
600 volts.
At least two phases
Check to make sure that the victim is not still in contact with the electricity.

29. The primary function of a power transformer is to provide...
Clamp-on ammeter.
Full-load - three-phase voltage.
Stator windings.
At the source transformer.

30. The transformer used only to measure voltage is a...
Provides single-phase power to smaller loads such as lights - heaters - etc.
No.6 AWG.
Potential transformer.
Second-degree burn.

31. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Grounded phase and ground fault devices were not operating.
Draw less current.
Because less current flowing at high voltage causes less line loss per kilowatt.

32. Compared to the secondary of a loaded - step-down transformer - the primary has...
A grounding resistor.
A.C.
Squirrel-cage induction motor.
Lower current and higher voltage.

33. A transformer with a 1:1 ratio is usually a (an)...
Reverse its rotation.
Isolation transformer.
Zero amps.
2000 watts

34. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Full-load - three-phase voltage.
Grounded phase and ground fault devices were not operating.
Short-circuited after power has been removed.
The capacitors should be discharged.

35. Current that changes periodically in direction is...
Alternating current.
100 volts.
Electro-magnetism for their operation.
Lower current and higher voltage.

36. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Reverse any two-phase leads.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Isolation transformer.

37. 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?
Potential transformer.
The chest should rise or inflate.
150 turns.
Current that changes constantly in magnitude and periodically in direction.

38. 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?
The sum of the two capacitors.
Tied together
12 to 15 times a minute.
75 turns.

39. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
200 volts AC.
Reverse its rotation.
Tied together

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

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41. 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?
Nearly constant.
Transformer
600 volts.
100 turns.

42. 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?
Continuous.
Stator windings.
480 volts.
75 turns.

43. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
It provides good speed control.
Disconnect the frame-grounding conductor.
They must be installed at least 7 feet above the ground.

44. What type motor is a wound-rotor induction motor?
600 volts.
A.C.
Current that changes constantly in magnitude and periodically in direction.
Transformer

45. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
A step-up transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.
Inductance.
277 volts.

46. 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?
800 volts.
Transformers.
5:1
Disconnect the frame-grounding conductor.

47. Current in an AC circuit may be measured by...
Four times less than that of the secondary.
The motor rotation is reversed.
H terminals.
Clamp-on ammeter.

48. 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.
480 volts.
277 volts.
5:1.
5:1

49. 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...
Carotid pulse - which is located in the neck next to the Adam's apple.
Isolation transformer.
25 feet.
100 volts.

50. Which of the following does a squirrel cage induction motor have?
Continuous.
Draw less current.
No.6 AWG.
Stator windings.