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AC Theory

Instructions:

Answer 50 questions in 30 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. Not a symptom of electrical shock?.
Hyperventilation.
Inductance.
No.6 AWG.
Transformer

2. 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?
Reverse its rotation.
Inductance.
Stator windings.
100 turns.

3. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Hyperventilation.
Zero amps.
A step-up transformer.

4. The speed of an alternating current - squirrel-cage induction motor is...
Disconnect the frame-grounding conductor.
A.C.
Circuit Breaker.
Nearly constant.

5. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Shunted and taped
A grounding resistor.
Cut around clothing that has adhered to the burned area.

6. What should the duty rating of a grounding resistor be?
Four times less than that of the secondary.
Full-load - three-phase voltage.
Continuous.
3 -979 Volts.

7. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Cut around clothing that has adhered to the burned area.
75 turns.
2000 watts

8. 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...
Reverse its rotation.
Allow for metering voltage and Current.
Draw less current.
Second-degree burn.

9. High voltage is used to transmit power over long distances...
Hyperventilation.
Current changing constantly in magnitude and periodically in direction.
Because less current flowing at high voltage causes less line loss per kilowatt.
Continuous.

10. 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?
100 volts.
Squirrel-cage induction motor.
150 turns.
5:1

11. The property of an electrical circuit that opposes any change in voltage is called...
H terminals.
At the source transformer.
Capacitance.
Circuit Breaker.

12. 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?
Isolation transformer.
3 -979 Volts.
Current changing constantly in magnitude and periodically in direction.
Clamp-on ammeter.

13. The primary function of a power transformer is to provide...
Shunted and taped
100 turns.
75 turns.
Full-load - three-phase voltage.

14. Compared to the secondary of a loaded - step-down transformer - the primary has...
15 feet off the ground.
2000 watts
No.6 AWG.
Lower current and higher voltage.

15. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
The motor rotation is reversed.
Reverse any two-phase leads.
They should be made by the same manufacturer.
2000 watts

16. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
X.
60 cycles per second (60 Hertz).
Short-circuited after power has been removed.
75 turns.

17. What type of 3-phase AC motor is used most often around a mine?
The sum of the two capacitors.
Squirrel-cage induction motor.
The current will read zero.
At the source transformer.

18. 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.
5:1
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
15 feet off the ground.
X.

19. 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?
Nearly constant.
An electromagnet.
Squirrel-cage rotor.
200 volts AC.

20. A wound-rotor induction motor has all the following EXCEPT...
1 amp.
Squirrel-cage rotor.
12 to 15 times a minute.
Four times less than that of the secondary.

21. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
150 turns.
1 amp.
Capacitance.
Transformers.

22. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Isolation transformer.
The motor rotation is reversed.
Reverse any two-phase leads.
They should be made by the same manufacturer.

23. A burn causing a blister is classified as a...
Four times less than that of the secondary.
5:1
Second-degree burn.
Larger than that found in the primary winding.

24. What steps up or steps down AC voltage?
Nearly constant.
200 volts AC.
A device used to store electrical energy.
Transformer

25. How do you change the direction of a 3-phase AC motor?
The chest should rise or inflate.
Full-load - three-phase voltage.
Reverse any two-phase leads.
Cut around clothing that has adhered to the burned area.

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

27. 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...
The chest should rise or inflate.
Current that changes constantly in magnitude and periodically in direction.
100 volts.
Electro-magnetism for their operation.

28. The primary leads of a single-phase transformer should be connected to the...
H terminals.
25 feet.
Four times less than that of the secondary.
277 volts.

29. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
Zero amps.
The motor rotation is reversed.
7 -630 volts.

30. 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.
Clamp-on ammeter.
Hyperventilation.
5:1.
Draw less current.

31. 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
800 volts.
Lower current and higher voltage
Second-degree burn.

32. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
12 to 15 times a minute.
A device used to store electrical energy.
Current that changes constantly in magnitude and periodically in direction.

33. 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?
Stator windings.
Draw less current.
75 turns.
Grounded phase and ground fault devices were not operating.

34. 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?
The capacitors should be discharged.
75 turns.
Cut around clothing that has adhered to the burned area.
Disconnect the frame-grounding conductor.

35. Not an acceptable method for the installations of surface transformers?
Circuit Breaker.
Current that changes constantly in magnitude and periodically in direction.
They must be installed at least 7 feet above the ground.
The motor rotation is reversed.

36. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
75 turns.
Transformer
200 volts AC.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

37. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
25 feet.
The current will read zero.
No.6 AWG.
5:1.

38. The standard frequency of power supplied by the power company is...
Alternating current.
60 cycles per second (60 Hertz).
They should be made by the same manufacturer.
75 turns.

39. A solenoid coil is...
Kilovolt ampere (KVA).
Reverse its rotation.
An electromagnet.
The capacitors should be discharged.

40. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
A.C.
Carotid pulse - which is located in the neck next to the Adam's apple.
The chest should rise or inflate.
Potential transformer.

41. Current in an AC circuit may be measured by...
A grounding resistor.
Clamp-on ammeter.
No.6 AWG.
Disconnect the frame-grounding conductor.

42. The combined capacitance of two capacitors in parallel is...
60 cycles per second (60 Hertz).
At least two phases
No.6 AWG.
The sum of the two capacitors.

43. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
At least two phases
At the source transformer.
7 -630 volts.
277 volts.

44. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
A step-up transformer.
An electrical shock hazard may exist.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

45. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
They should be made by the same manufacturer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Two speeds

46. 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...
Draw less current.
Kilovolt ampere (KVA).
Clamp-on ammeter.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

47. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Transformer
15 feet off the ground.
60 cycles per second (60 Hertz).
They should be made by the same manufacturer.

48. All transformers step voltage up or down by...
Inductance.
Grounded phase and ground fault devices were not operating.
An electromagnet.
150 turns.

49. What is a capacitor?
Squirrel-cage induction motor.
Second-degree burn.
75 turns.
A device used to store electrical energy.

50. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
200 volts AC.
25 feet.
Inductance.
Draw less current.