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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 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.
Isolation transformer.
The current will read zero.
Squirrel-cage induction motor.

2. The speed of an alternating current - squirrel-cage induction motor is...
A step-up transformer.
Derive a neutral for grounding purposes.
Nearly constant.
1 amp.

3. At what rate should mouth-to-mouth resuscitation be applied?
75 turns.
12 to 15 times a minute.
2000 watts
Transformers.

4. Operating coils - motors - transformers - relays and solenoids depend upon...
Transformer
Shunted and taped
Two speeds
Electro-magnetism for their operation.

5. A wound-rotor induction motor has all the following EXCEPT...
3 -979 Volts.
Squirrel-cage rotor.
It provides good speed control.
1 amp.

6. Define alternating current...
A.C.
Four times less than that of the secondary.
Tied together
Current changing constantly in magnitude and periodically in direction.

7. 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
Nearly constant.
Allow for metering voltage and Current.
100 turns.

8. The primary function of a power transformer is to provide...
Larger than that found in the primary winding.
Full-load - three-phase voltage.
A.C.
Current that changes constantly in magnitude and periodically in direction.

9. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
277 volts.
Second-degree burn.
Electro-magnetism for their operation.
25 feet.

10. A solenoid coil is...
Inductance.
60 Hertz
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
An electromagnet.

11. Current that changes periodically in direction is...
2000 watts
Clamp-on ammeter.
Alternating current.
Transformer

12. The property of an electrical circuit that opposes any change in voltage is called...
Cut around clothing that has adhered to the burned area.
75 turns.
Capacitance.
Reverse its rotation.

13. How do you change the direction of a 3-phase AC motor?
Transformer
Shunted and taped
Reverse any two-phase leads.
Second-degree burn.

14. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
15 feet off the ground.
200 volts AC.
They should be made by the same manufacturer.

15. The standard frequency of power supplied by the power company is...
200 volts AC.
Four times less than that of the secondary.
60 cycles per second (60 Hertz).
A device used to store electrical energy.

16. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Draw less current.
The current will read zero.
The motor rotation is reversed.
It provides good speed control.

17. If any two-phase wires are reversed on a three-phase motor - the motor will...
Electro-magnetism for their operation.
Reverse any two-phase leads.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Reverse its rotation.

18. 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?
100 turns.
3 -979 Volts.
800 volts.
Lower current and higher voltage

19. 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?
Inductance.
75 turns.
Tied together
Stator windings.

20. What is the danger when working around capacitors?
An electrical shock hazard may exist.
Squirrel-cage rotor.
600 volts.
Tied together

21. 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?
Four times less than that of the secondary.
5:1.
100 volts.
75 turns.

22. Alternating current may be defined as...
Kilovolt ampere (KVA).
Current that changes constantly in magnitude and periodically in direction.
1 amp.
Two speeds

23. A burn causing a blister is classified as a...
Allow for metering voltage and Current.
Transformer
Second-degree burn.
Two speeds

24. What type motor is a wound-rotor induction motor?
Lower current and higher voltage.
A.C.
Nearly constant.
Provides single-phase power to smaller loads such as lights - heaters - etc.

25. 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...
At least two phases
It provides good speed control.
25 feet.
Draw less current.

26. What type of 3-phase AC motor is used most often around a mine?
Alternating current.
Squirrel-cage induction motor.
Derive a neutral for grounding purposes.
Second-degree burn.

27. 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...
Squirrel-cage induction motor.
The chest should rise or inflate.
5:1
Tied together

28. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
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.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Nearly constant.

29. Current in an AC circuit may be measured by...
Clamp-on ammeter.
They should be made by the same manufacturer.
Squirrel-cage induction motor.
480 volts.

30. Compared to the secondary of a loaded - step-down transformer - the primary has...
1 amp.
Reverse its rotation.
Lower current and higher voltage
Short-circuited after power has been removed.

31. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
7 -630 volts.
Larger than that found in the primary winding.
3 -979 Volts.
A step-up transformer.

32. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
12 to 15 times a minute.
Because less current flowing at high voltage causes less line loss per kilowatt.
3 -979 Volts.

33. 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?
Continuous.
600 volts.
Current that changes constantly in magnitude and periodically in direction.
Lower current and higher voltage

34. 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?
2000 watts
1 amp.
200 volts AC.
Continuous.

35. A transformer with a 1:1 ratio is usually a (an)...
2000 watts
5:1.
Current changing constantly in magnitude and periodically in direction.
Isolation transformer.

36. 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?
150 turns.
15 feet off the ground.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
A step-up transformer.

37. High voltage is used to transmit power over long distances...
Short-circuited after power has been removed.
Because less current flowing at high voltage causes less line loss per kilowatt.
Carotid pulse - which is located in the neck next to the Adam's apple.
2000 watts

38. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Potential transformer.
Disconnect the frame-grounding conductor.
Draw less current.
The motor rotation is reversed.

39. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
Transformer
The sum of the two capacitors.
A step-up transformer.

40. Compared to the secondary of a loaded - step-down transformer - the primary has...
Because less current flowing at high voltage causes less line loss per kilowatt.
60 cycles per second (60 Hertz).
The capacitors should be discharged.
Lower current and higher voltage.

41. 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.
5:1.
12 to 15 times a minute.
Two speeds

42. 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...
100 volts.
75 turns.
200 volts AC.
Nearly constant.

43. The secondary windings on a 10:1 step-down transformer will have a wire size...
3 -979 Volts.
200 volts AC.
Larger than that found in the primary winding.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

44. A control power transformer...
75 turns.
Provides single-phase power to smaller loads such as lights - heaters - etc.
The sum of the two capacitors.
Alternating current.

45. AC voltage is raised or lowered by means of...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Transformers.
Inductance.
15 feet off the ground.

46. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Clamp-on ammeter.
H terminals.
Grounded phase and ground fault devices were not operating.

47. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Lower current and higher voltage
A.C.
A step-up transformer.
Shunted and taped

48. Current transformers - or CT's - are used to...
They should be made by the same manufacturer.
An electrical shock hazard may exist.
7 -630 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

49. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
60 Hertz
X.
The current will read zero.
277 volts.

50. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
Zero amps.
Current changing constantly in magnitude and periodically in direction.
Cut around clothing that has adhered to the burned area.