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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. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
Short-circuited after power has been removed.
75 turns.
An electromagnet.

2. When not connected to a load - the secondary leads of a current transformer should be...
A step-up transformer.
Allow for metering voltage and Current.
Shunted and taped
Lower current and higher voltage.

3. 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...
60 Hertz
5:1.
7 -630 volts.
Tied together

4. A control power transformer...
Disconnect the frame-grounding conductor.
Provides single-phase power to smaller loads such as lights - heaters - etc.
60 Hertz
Two speeds

5. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Larger than that found in the primary winding.
Hyperventilation.
5:1.

6. 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?
12 to 15 times a minute.
75 turns.
X.
Check to make sure that the victim is not still in contact with the electricity.

7. All transformers step voltage up or down by...
Inductance.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Cut around clothing that has adhered to the burned area.
Circuit Breaker.

8. A burn causing a blister is classified as a...
3 -979 Volts.
Second-degree burn.
Zero amps.
They should be made by the same manufacturer.

9. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
100 volts.
150 turns.
25 feet.
Hyperventilation.

10. Not true about AC power?
It provides good speed control.
H terminals.
Potential transformer.
Continuous.

11. The speed of an alternating current - squirrel-cage induction motor is...
100 volts.
Tied together
Squirrel-cage induction motor.
Nearly constant.

12. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Disconnect the frame-grounding conductor.
7 -630 volts.
Shunted and taped

13. Current that changes periodically in direction is...
Cut around clothing that has adhered to the burned area.
Disconnect the frame-grounding conductor.
Two speeds
Alternating current.

14. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Alternating current.
A device used to store electrical energy.
Zero amps.

15. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
15 feet off the ground.
No.6 AWG.
Capacitance.

16. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Circuit Breaker.
277 volts.
2000 watts
No.6 AWG.

17. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
5:1.
Transformers.
H terminals.

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

19. High voltage is used to transmit power over long distances...
Lower current and higher voltage
Because less current flowing at high voltage causes less line loss per kilowatt.
The current will read zero.
Reverse its rotation.

20. 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...
Two speeds
Capacitance.
100 volts.
Draw less current.

21. A wound-rotor induction motor has all the following EXCEPT...
Reverse any two-phase leads.
Alternating current.
1 amp.
Squirrel-cage rotor.

22. 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...
Inductance.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Larger than that found in the primary winding.
Draw less current.

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.
5:1.
Stator windings.
Carotid pulse - which is located in the neck next to the Adam's apple.
75 turns.

24. The combined capacitance of two capacitors in parallel is...
Squirrel-cage induction motor.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The sum of the two capacitors.
Because less current flowing at high voltage causes less line loss per kilowatt.

25. What type motor is a wound-rotor induction motor?
5:1
Alternating current.
A.C.
Capacitance.

26. What is the first step to be followed in aiding a victim of electrical shock?
Check to make sure that the victim is not still in contact with the electricity.
Reverse its rotation.
An electrical shock hazard may exist.
Tied together

27. The transformer used only to measure voltage is a...
Reverse its rotation.
1 amp.
Allow for metering voltage and Current.
Potential transformer.

28. Compared to the secondary of a loaded - step-down transformer - the primary has...
Short-circuited after power has been removed.
Lower current and higher voltage
They should be made by the same manufacturer.
Two speeds

29. At what rate should mouth-to-mouth resuscitation be applied?
Continuous.
1 amp.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
12 to 15 times a minute.

30. The primary leads of a single-phase transformer should be connected to the...
200 volts AC.
H terminals.
600 volts.
No.6 AWG.

31. The standard frequency of alternating current used at a mine is...
60 cycles per second (60 Hertz).
200 volts AC.
Full-load - three-phase voltage.
60 Hertz

32. 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?
At the source transformer.
Grounded phase and ground fault devices were not operating.
3 -979 Volts.
25 feet.

33. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Derive a neutral for grounding purposes.
15 feet off the ground.
75 turns.
No.6 AWG.

34. 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.
The current will read zero.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
At least two phases

35. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
It provides good speed control.
1 amp.
Capacitance.
Tied together

36. 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?
75 turns.
5:1.
Inductance.
The capacitors should be discharged.

37. 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?
Clamp-on ammeter.
200 volts AC.
60 cycles per second (60 Hertz).
75 turns.

38. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
100 volts.
A device used to store electrical energy.
60 Hertz
Zero amps.

39. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Electro-magnetism for their operation.
The motor rotation is reversed.
75 turns.
Lower current and higher voltage.

40. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Derive a neutral for grounding purposes.
Lower current and higher voltage.
Two speeds
Tied together

41. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Short-circuited after power has been removed.
X.
Electro-magnetism for their operation.
Reverse any two-phase leads.

42. What steps up or steps down AC voltage?
2000 watts
Transformer
Short-circuited after power has been removed.
100 turns.

43. Define alternating current...
A device used to store electrical energy.
Current changing constantly in magnitude and periodically in direction.
600 volts.
Four times less than that of the secondary.

44. What is the danger when working around capacitors?
Kilovolt ampere (KVA).
100 volts.
Full-load - three-phase voltage.
An electrical shock hazard may exist.

45. AC voltage is raised or lowered by means of...
150 turns.
The chest should rise or inflate.
Transformers.
Transformer

46. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
The chest should rise or inflate.
100 volts.
The capacitors should be discharged.

47. 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
Draw less current.
It provides good speed control.
They must be installed at least 7 feet above the ground.

48. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The motor rotation is reversed.
Transformer
An electrical shock hazard may exist.
The capacitors should be discharged.

49. What should the duty rating of a grounding resistor be?
Second-degree burn.
Cut around clothing that has adhered to the burned area.
They must be installed at least 7 feet above the ground.
Continuous.

50. What is a capacitor?
H terminals.
200 volts AC.
A device used to store electrical energy.
Potential transformer.