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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. 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...
5:1
Nearly constant.
At least two phases
Tied together

2. 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.
A device used to store electrical energy.
7 -630 volts.
Derive a neutral for grounding purposes.
5:1

3. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
100 turns.
7 -630 volts.
25 feet.
A step-up transformer.

4. The size of a transformer is measured in...
25 feet.
Nearly constant.
Kilovolt ampere (KVA).
15 feet off the ground.

5. 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.
Two speeds
At the source transformer.
Tied together

6. A wound-rotor induction motor has all the following EXCEPT...
Tied together
25 feet.
Squirrel-cage rotor.
They must be installed at least 7 feet above the ground.

7. Current in an AC circuit may be measured by...
X.
Full-load - three-phase voltage.
Clamp-on ammeter.
At least two phases

8. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Four times less than that of the secondary.
5:1.
Short-circuited after power has been removed.
Continuous.

9. The main function of CT's and PT's on a main substation is to...
25 feet.
Allow for metering voltage and Current.
277 volts.
Zero amps.

10. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Electro-magnetism for their operation.
They should be made by the same manufacturer.
A step-up transformer.
75 turns.

11. The secondary windings on a 10:1 step-down transformer will have a wire size...
A grounding resistor.
150 turns.
Derive a neutral for grounding purposes.
Larger than that found in the primary winding.

12. A burn causing a blister is classified as a...
At least two phases
No.6 AWG.
Short-circuited after power has been removed.
Second-degree burn.

13. 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.
150 turns.
5:1
25 feet.

14. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Squirrel-cage rotor.
Grounded phase and ground fault devices were not operating.
Check to make sure that the victim is not still in contact with the electricity.

15. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Transformer
Squirrel-cage rotor.
60 cycles per second (60 Hertz).

16. A solenoid coil is...
Reverse any two-phase leads.
Continuous.
An electromagnet.
No.6 AWG.

17. AC voltage is raised or lowered by means of...
Tied together
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The motor rotation is reversed.
Transformers.

18. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
The sum of the two capacitors.
Isolation transformer.
Transformers.

19. 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.
A device used to store electrical energy.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Check to make sure that the victim is not still in contact with the electricity.

20. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
277 volts.
480 volts.
7 -630 volts.
Hyperventilation.

21. Not an acceptable method for the installations of surface transformers?
Current changing constantly in magnitude and periodically in direction.
60 Hertz
Hyperventilation.
They must be installed at least 7 feet above the ground.

22. 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?
The current will read zero.
75 turns.
No.6 AWG.
Squirrel-cage rotor.

23. 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?
The capacitors should be discharged.
Transformer
12 to 15 times a minute.
100 turns.

24. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Alternating current.
An electromagnet.
The motor rotation is reversed.
5:1

25. 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?
Zero amps.
150 turns.
Because less current flowing at high voltage causes less line loss per kilowatt.
600 volts.

26. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Circuit Breaker.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
2000 watts
1 amp.

27. Current transformers - or CT's - are used to...
5:1
X.
Tied together
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

28. What is a capacitor?
A device used to store electrical energy.
A grounding resistor.
The motor rotation is reversed.
Short-circuited after power has been removed.

29. 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?
Inductance.
60 Hertz
150 turns.
200 volts AC.

30. 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?
5:1
800 volts.
Continuous.
Two speeds

31. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Continuous.
A.C.
At least two phases
Shunted and taped

32. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Allow for metering voltage and Current.
A step-up transformer.
100 turns.
Reverse any two-phase leads.

33. Not true about AC power?
12 to 15 times a minute.
It provides good speed control.
5:1.
Kilovolt ampere (KVA).

34. The property of an electrical circuit that opposes any change in voltage is called...
75 turns.
X.
Circuit Breaker.
Capacitance.

35. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
An electromagnet.
Cut around clothing that has adhered to the burned area.
The capacitors should be discharged.
X.

36. 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...
Larger than that found in the primary winding.
Allow for metering voltage and Current.
Draw less current.
The sum of the two capacitors.

37. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
Shunted and taped
Cut around clothing that has adhered to the burned area.
Isolation transformer.

38. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Kilovolt ampere (KVA).
Inductance.
Isolation transformer.

39. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Capacitance.
Disconnect the frame-grounding conductor.
75 turns.

40. How should clothing be removed from a burn?
Provides single-phase power to smaller loads such as lights - heaters - etc.
Potential transformer.
Cut around clothing that has adhered to the burned area.
Current that changes constantly in magnitude and periodically in direction.

41. Where should grounding resistors be located?
Capacitance.
At the source transformer.
The chest should rise or inflate.
The sum of the two capacitors.

42. Alternating current may be defined as...
Transformer
Zero amps.
Current that changes constantly in magnitude and periodically in direction.
5:1

43. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Lower current and higher voltage
100 volts.
Inductance.

44. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Zero amps.
Lower current and higher voltage
Four times less than that of the secondary.
Shunted and taped

45. Which of the following does a squirrel cage induction motor have?
277 volts.
75 turns.
600 volts.
Stator windings.

46. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Current changing constantly in magnitude and periodically in direction.
Clamp-on ammeter.
The chest should rise or inflate.
Hyperventilation.

47. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Four times less than that of the secondary.
Current that changes constantly in magnitude and periodically in direction.
Reverse any two-phase leads.

48. Current that changes periodically in direction is...
A device used to store electrical energy.
Alternating current.
7 -630 volts.
The chest should rise or inflate.

49. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Tied together
Grounded phase and ground fault devices were not operating.
Provides single-phase power to smaller loads such as lights - heaters - etc.
The chest should rise or inflate.

50. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Full-load - three-phase voltage.
25 feet.
Current changing constantly in magnitude and periodically in direction.
480 volts.