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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. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Derive a neutral for grounding purposes.
100 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
600 volts.

2. Define alternating current...
Second-degree burn.
1 amp.
Current changing constantly in magnitude and periodically in direction.
800 volts.

3. What steps up or steps down AC voltage?
200 volts AC.
Inductance.
Transformer
Squirrel-cage induction motor.

4. Which of the following does a squirrel cage induction motor have?
Stator windings.
Capacitance.
They should be made by the same manufacturer.
Tied together

5. The secondary windings on a 10:1 step-down transformer will have a wire size...
200 volts AC.
1 amp.
Larger than that found in the primary winding.
Grounded phase and ground fault devices were not operating.

6. A wound-rotor induction motor has all the following EXCEPT...
Cut around clothing that has adhered to the burned area.
Squirrel-cage rotor.
It provides good speed control.
Lower current and higher voltage.

7. 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.
The current will read zero.
Four times less than that of the secondary.
Second-degree burn.

8. The primary leads of a single-phase transformer should be connected to the...
Zero amps.
H terminals.
The sum of the two capacitors.
Kilovolt ampere (KVA).

9. 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.
Squirrel-cage induction motor.
Nearly constant.
Because less current flowing at high voltage causes less line loss per kilowatt.

10. 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.
100 turns.
H terminals.
5:1
25 feet.

11. 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?
200 volts AC.
75 turns.
Reverse its rotation.
Short-circuited after power has been removed.

12. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The capacitors should be discharged.
Shunted and taped
Provides single-phase power to smaller loads such as lights - heaters - etc.
The chest should rise or inflate.

13. Alternating current may be defined as...
Potential transformer.
The chest should rise or inflate.
Squirrel-cage rotor.
Current that changes constantly in magnitude and periodically in direction.

14. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
3 -979 Volts.
Four times less than that of the secondary.
Zero amps.

15. What type of 3-phase AC motor is used most often around a mine?
Shunted and taped
Kilovolt ampere (KVA).
Squirrel-cage induction motor.
Circuit Breaker.

16. If any two-phase wires are reversed on a three-phase motor - the motor will...
12 to 15 times a minute.
Derive a neutral for grounding purposes.
Reverse its rotation.
They must be installed at least 7 feet above the ground.

17. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
25 feet.
No.6 AWG.
Lower current and higher voltage.

18. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
150 turns.
Zero amps.
Transformers.
Lower current and higher voltage

19. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Inductance.
Second-degree burn.
Because less current flowing at high voltage causes less line loss per kilowatt.

20. A burn causing a blister is classified as a...
Potential transformer.
Check to make sure that the victim is not still in contact with the electricity.
Two speeds
Second-degree burn.

21. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Electro-magnetism for their operation.
Carotid pulse - which is located in the neck next to the Adam's apple.
5:1.

22. Not a symptom of electrical shock?.
Hyperventilation.
Second-degree burn.
Squirrel-cage rotor.
Disconnect the frame-grounding conductor.

23. 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?
200 volts AC.
Squirrel-cage induction motor.
H terminals.
Capacitance.

24. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Continuous.
Alternating current.
X.
They should be made by the same manufacturer.

25. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
100 turns.
60 cycles per second (60 Hertz).
X.

26. The property of an electric circuit that opposes any change in current is called...
Current that changes constantly in magnitude and periodically in direction.
Reverse its rotation.
Potential transformer.
Inductance.

27. A solenoid coil is...
Carotid pulse - which is located in the neck next to the Adam's apple.
800 volts.
277 volts.
An electromagnet.

28. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
60 Hertz
A grounding resistor.
Reverse its rotation.

29. 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.
Four times less than that of the secondary.
Clamp-on ammeter.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

30. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Short-circuited after power has been removed.
At least two phases
5:1.
Allow for metering voltage and Current.

31. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Potential transformer.
480 volts.
A step-up transformer.
Disconnect the frame-grounding conductor.

32. How do you change the direction of a 3-phase AC motor?
Transformer
Isolation transformer.
Alternating current.
Reverse any two-phase leads.

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

34. The transformer used only to measure voltage is a...
Draw less current.
5:1.
Zero amps.
Potential transformer.

35. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Lower current and higher voltage.
An electromagnet.
Four times less than that of the secondary.

36. What type motor is a wound-rotor induction motor?
Allow for metering voltage and Current.
A.C.
Circuit Breaker.
The chest should rise or inflate.

37. Operating coils - motors - transformers - relays and solenoids depend upon...
Inductance.
Larger than that found in the primary winding.
The capacitors should be discharged.
Electro-magnetism for their operation.

38. AC voltage is raised or lowered by means of...
75 turns.
Transformers.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
A device used to store electrical energy.

39. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The current will read zero.
Isolation transformer.
5:1.
Electro-magnetism for their operation.

40. 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?
Electro-magnetism for their operation.
3 -979 Volts.
12 to 15 times a minute.
Transformer

41. Where should grounding resistors be located?
Lower current and higher voltage
At the source transformer.
60 Hertz
Provides single-phase power to smaller loads such as lights - heaters - etc.

42. A control power transformer...
Stator windings.
Inductance.
Provides single-phase power to smaller loads such as lights - heaters - etc.
A step-up transformer.

43. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
They should be made by the same manufacturer.
480 volts.
Draw less current.
Transformers.

44. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Squirrel-cage rotor.
277 volts.
Isolation transformer.
Potential transformer.

45. The primary function of a power transformer is to provide...
Electro-magnetism for their operation.
Short-circuited after power has been removed.
Clamp-on ammeter.
Full-load - three-phase voltage.

46. The standard frequency of power supplied by the power company is...
75 turns.
Short-circuited after power has been removed.
2000 watts
60 cycles per second (60 Hertz).

47. Three-phase AC underground cables must be provided with overcurrent protection using a...
Four times less than that of the secondary.
Circuit Breaker.
7 -630 volts.
5:1.

48. The main function of CT's and PT's on a main substation is to...
Electro-magnetism for their operation.
Allow for metering voltage and Current.
Derive a neutral for grounding purposes.
Kilovolt ampere (KVA).

49. 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...
Shunted and taped
Tied together
Nearly constant.
Cut around clothing that has adhered to the burned area.

50. What is a capacitor?
Derive a neutral for grounding purposes.
Clamp-on ammeter.
Hyperventilation.
A device used to store electrical energy.