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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. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Shunted and taped
Draw less current.
The motor rotation is reversed.
Current changing constantly in magnitude and periodically in direction.

2. The main function of CT's and PT's on a main substation is to...
Inductance.
Allow for metering voltage and Current.
Draw less current.
The sum of the two capacitors.

3. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
A device used to store electrical energy.
480 volts.
Kilovolt ampere (KVA).
The current will read zero.

4. Current in an AC circuit may be measured by...
Reverse any two-phase leads.
2000 watts
Clamp-on ammeter.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

5. Not a symptom of electrical shock?.
Two speeds
600 volts.
A grounding resistor.
Hyperventilation.

6. The property of an electric circuit that opposes any change in current is called...
Inductance.
25 feet.
Derive a neutral for grounding purposes.
100 turns.

7. The purpose of a zig-zag transformer is to...
277 volts.
75 turns.
Derive a neutral for grounding purposes.
Nearly constant.

8. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Full-load - three-phase voltage.
Circuit Breaker.
Disconnect the frame-grounding conductor.
At least two phases

9. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
They should be made by the same manufacturer.
60 cycles per second (60 Hertz).
Grounded phase and ground fault devices were not operating.
Draw less current.

10. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
3 -979 Volts.
Transformer
Four times less than that of the secondary.
They must be installed at least 7 feet above the ground.

11. Define alternating current...
Larger than that found in the primary winding.
Two speeds
Current changing constantly in magnitude and periodically in direction.
Because less current flowing at high voltage causes less line loss per kilowatt.

12. High voltage is used to transmit power over long distances...
An electromagnet.
60 Hertz
Because less current flowing at high voltage causes less line loss per kilowatt.
Stator windings.

13. How should clothing be removed from a burn?
A grounding resistor.
Cut around clothing that has adhered to the burned area.
Two speeds
A.C.

14. Current that changes periodically in direction is...
Continuous.
Squirrel-cage induction motor.
Alternating current.
Inductance.

15. 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?
A grounding resistor.
800 volts.
Squirrel-cage induction motor.
Continuous.

16. 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?
Grounded phase and ground fault devices were not operating.
800 volts.
Draw less current.
3 -979 Volts.

17. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
277 volts.
600 volts.
Alternating current.

18. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Squirrel-cage induction motor.
Inductance.
The chest should rise or inflate.
An electromagnet.

19. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
75 turns.
Current that changes constantly in magnitude and periodically in direction.
Inductance.

20. What steps up or steps down AC voltage?
Current that changes constantly in magnitude and periodically in direction.
Continuous.
Transformer
Cut around clothing that has adhered to the burned area.

21. AC voltage is raised or lowered by means of...
Transformers.
A.C.
Cut around clothing that has adhered to the burned area.
277 volts.

22. All transformers step voltage up or down by...
Short-circuited after power has been removed.
Inductance.
They must be installed at least 7 feet above the ground.
100 turns.

23. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Inductance.
Disconnect the frame-grounding conductor.
Because less current flowing at high voltage causes less line loss per kilowatt.

24. 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...
Zero amps.
Lower current and higher voltage
Tied together
Second-degree burn.

25. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
2000 watts
Derive a neutral for grounding purposes.
5:1.
Allow for metering voltage and Current.

26. The speed of an alternating current - squirrel-cage induction motor is...
200 volts AC.
Transformers.
Nearly constant.
The current will read zero.

27. 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?
Full-load - three-phase voltage.
150 turns.
Inductance.
An electrical shock hazard may exist.

28. If any two-phase wires are reversed on a three-phase motor - the motor will...
Inductance.
Reverse its rotation.
Reverse any two-phase leads.
Two speeds

29. Not true about AC power?
An electromagnet.
It provides good speed control.
Reverse its rotation.
60 cycles per second (60 Hertz).

30. 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...
Continuous.
Circuit Breaker.
Draw less current.
The current will read zero.

31. The size of a transformer is measured in...
200 volts AC.
Kilovolt ampere (KVA).
25 feet.
12 to 15 times a minute.

32. 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?
Inductance.
They must be installed at least 7 feet above the ground.
75 turns.
Squirrel-cage rotor.

33. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
150 turns.
Isolation transformer.
It provides good speed control.
1 amp.

34. A control power transformer...
The sum of the two capacitors.
Allow for metering voltage and Current.
Provides single-phase power to smaller loads such as lights - heaters - etc.
X.

35. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Lower current and higher voltage.
100 volts.
No.6 AWG.
The current will read zero.

36. When not connected to a load - the secondary leads of a current transformer should be...
600 volts.
Transformers.
Shunted and taped
Short-circuited after power has been removed.

37. The transformer used only to measure voltage is a...
Shunted and taped
Kilovolt ampere (KVA).
It provides good speed control.
Potential transformer.

38. What type motor is a wound-rotor induction motor?
A.C.
Shunted and taped
Second-degree burn.
The chest should rise or inflate.

39. The combined capacitance of two capacitors in parallel is...
Transformer
The sum of the two capacitors.
Transformers.
Second-degree burn.

40. 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?
75 turns.
150 turns.
Electro-magnetism for their operation.
They should be made by the same manufacturer.

41. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
The capacitors should be discharged.
A step-up transformer.
At the source transformer.
277 volts.

42. 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.
480 volts.
Allow for metering voltage and Current.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

43. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Zero amps.
At least two phases
12 to 15 times a minute.
The current will read zero.

44. Where should grounding resistors be located?
480 volts.
150 turns.
Alternating current.
At the source transformer.

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

46. A burn causing a blister is classified as a...
Kilovolt ampere (KVA).
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Draw less current.
Second-degree burn.

47. What should the duty rating of a grounding resistor be?
Continuous.
Tied together
Check to make sure that the victim is not still in contact with the electricity.
Transformers.

48. Compared to the secondary of a loaded - step-down transformer - the primary has...
75 turns.
Four times less than that of the secondary.
Full-load - three-phase voltage.
Lower current and higher voltage.

49. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
2000 watts
Carotid pulse - which is located in the neck next to the Adam's apple.
60 Hertz
277 volts.

50. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Larger than that found in the primary winding.
X.
It provides good speed control.
277 volts.