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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. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Capacitance.
Larger than that found in the primary winding.
100 volts.

2. The standard frequency of alternating current used at a mine is...
60 Hertz
Circuit Breaker.
Derive a neutral for grounding purposes.
At the source transformer.

3. 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?
Provides single-phase power to smaller loads such as lights - heaters - etc.
100 volts.
H terminals.
150 turns.

4. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
25 feet.
Clamp-on ammeter.
Current changing constantly in magnitude and periodically in direction.

5. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
No.6 AWG.
Potential transformer.
The sum of the two capacitors.

6. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Potential transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Full-load - three-phase voltage.
H terminals.

7. Current that changes periodically in direction is...
Hyperventilation.
Alternating current.
The capacitors should be discharged.
Draw less current.

8. What is the first step to be followed in aiding a victim of electrical shock?
Inductance.
100 turns.
Check to make sure that the victim is not still in contact with the electricity.
Reverse any two-phase leads.

9. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
The motor rotation is reversed.
X.
Transformer
Second-degree burn.

10. Current transformers - or CT's - are used to...
100 volts.
Allow for metering voltage and Current.
150 turns.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

11. 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?
1 amp.
200 volts AC.
Continuous.
Larger than that found in the primary winding.

12. A burn causing a blister is classified as a...
5:1
Second-degree burn.
The current will read zero.
75 turns.

13. What steps up or steps down AC voltage?
The capacitors should be discharged.
Transformer
Squirrel-cage induction motor.
The chest should rise or inflate.

14. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
150 turns.
The chest should rise or inflate.
No.6 AWG.
Draw less current.

15. The combined capacitance of two capacitors in parallel is...
Four times less than that of the secondary.
X.
100 volts.
The sum of the two capacitors.

16. The property of an electric circuit that opposes any change in current is called...
A device used to store electrical energy.
Inductance.
Because less current flowing at high voltage causes less line loss per kilowatt.
Transformers.

17. What should the duty rating of a grounding resistor be?
Continuous.
The motor rotation is reversed.
7 -630 volts.
60 cycles per second (60 Hertz).

18. 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.
Shunted and taped
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Lower current and higher voltage.

19. At what rate should mouth-to-mouth resuscitation be applied?
Current changing constantly in magnitude and periodically in direction.
An electromagnet.
12 to 15 times a minute.
2000 watts

20. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Draw less current.
Squirrel-cage induction motor.
277 volts.
Capacitance.

21. Define alternating current...
Carotid pulse - which is located in the neck next to the Adam's apple.
Full-load - three-phase voltage.
Transformers.
Current changing constantly in magnitude and periodically in direction.

22. Not a symptom of electrical shock?.
Draw less current.
Transformers.
Hyperventilation.
Four times less than that of the secondary.

23. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Lower current and higher voltage
Potential transformer.
They should be made by the same manufacturer.
Zero amps.

24. 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?
600 volts.
An electrical shock hazard may exist.
Grounded phase and ground fault devices were not operating.
Isolation transformer.

25. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
800 volts.
Hyperventilation.
A step-up transformer.
Second-degree burn.

26. 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.
No.6 AWG.
Four times less than that of the secondary.
Hyperventilation.

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

28. 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?
Disconnect the frame-grounding conductor.
800 volts.
15 feet off the ground.
Circuit Breaker.

29. Not true about AC power?
800 volts.
60 Hertz
It provides good speed control.
No.6 AWG.

30. A solenoid coil is...
An electromagnet.
600 volts.
The current will read zero.
A grounding resistor.

31. Compared to the secondary of a loaded - step-down transformer - the primary has...
Draw less current.
Lower current and higher voltage
An electrical shock hazard may exist.
The sum of the two capacitors.

32. Not an acceptable method for the installations of surface transformers?
Alternating current.
They should be made by the same manufacturer.
Zero amps.
They must be installed at least 7 feet above the ground.

33. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Larger than that found in the primary winding.
Two speeds
Derive a neutral for grounding purposes.
5:1.

34. The purpose of a zig-zag transformer is to...
Isolation transformer.
Derive a neutral for grounding purposes.
The sum of the two capacitors.
Squirrel-cage rotor.

35. How should clothing be removed from a burn?
Inductance.
Nearly constant.
Reverse any two-phase leads.
Cut around clothing that has adhered to the burned area.

36. A transformer with a 1:1 ratio is usually a (an)...
A step-up transformer.
Isolation transformer.
600 volts.
60 Hertz

37. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
The current will read zero.
They should be made by the same manufacturer.
60 Hertz

38. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Shunted and taped
Two speeds
Provides single-phase power to smaller loads such as lights - heaters - etc.
No.6 AWG.

39. AC voltage is raised or lowered by means of...
60 Hertz
Transformers.
Short-circuited after power has been removed.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

40. The primary function of a power transformer is to provide...
The motor rotation is reversed.
5:1.
A device used to store electrical energy.
Full-load - three-phase voltage.

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

42. What is the danger when working around capacitors?
A grounding resistor.
Tied together
An electrical shock hazard may exist.
75 turns.

43. 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 cycles per second (60 Hertz).
Tied together
Draw less current.
The capacitors should be discharged.

44. 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?
Zero amps.
Allow for metering voltage and Current.
Current that changes constantly in magnitude and periodically in direction.
75 turns.

45. 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?
7 -630 volts.
Second-degree burn.
The current will read zero.
75 turns.

46. Which of the following does a squirrel cage induction motor have?
Stator windings.
150 turns.
7 -630 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.

47. 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...
They should be made by the same manufacturer.
Nearly constant.
Draw less current.
Circuit Breaker.

48. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Kilovolt ampere (KVA).
15 feet off the ground.
Zero amps.
200 volts AC.

49. 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.
60 cycles per second (60 Hertz).
Zero amps.

50. High voltage is used to transmit power over long distances...
The chest should rise or inflate.
The sum of the two capacitors.
Because less current flowing at high voltage causes less line loss per kilowatt.
200 volts AC.