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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. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
5:1.
Derive a neutral for grounding purposes.
At the source transformer.

2. What is the first step to be followed in aiding a victim of electrical shock?
Transformers.
The current will read zero.
Check to make sure that the victim is not still in contact with the electricity.
Because less current flowing at high voltage causes less line loss per kilowatt.

3. Three-phase AC underground cables must be provided with overcurrent protection using a...
Lower current and higher voltage.
At the source transformer.
75 turns.
Circuit Breaker.

4. When not connected to a load - the secondary leads of a current transformer should be...
12 to 15 times a minute.
Reverse its rotation.
Capacitance.
Shunted and taped

5. Which of the following does a squirrel cage induction motor have?
Second-degree burn.
Stator windings.
200 volts AC.
Four times less than that of the secondary.

6. A control power transformer...
Full-load - three-phase voltage.
Provides single-phase power to smaller loads such as lights - heaters - etc.
12 to 15 times a minute.
Inductance.

7. 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...
Tied together
Two speeds
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
An electromagnet.

8. The property of an electrical circuit that opposes any change in voltage is called...
Clamp-on ammeter.
Capacitance.
12 to 15 times a minute.
5:1

9. 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?
H terminals.
277 volts.
2000 watts
75 turns.

10. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
They should be made by the same manufacturer.
The capacitors should be discharged.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
X.

11. Current that changes periodically in direction is...
H terminals.
Alternating current.
The current will read zero.
Second-degree burn.

12. 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.
Capacitance.
Isolation transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

13. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
An electromagnet.
They should be made by the same manufacturer.
A grounding resistor.
Current that changes constantly in magnitude and periodically in direction.

14. All transformers step voltage up or down by...
A device used to store electrical energy.
Lower current and higher voltage.
Inductance.
Short-circuited after power has been removed.

15. The transformer used only to measure voltage is a...
Potential transformer.
Nearly constant.
Circuit Breaker.
Draw less current.

16. A burn causing a blister is classified as a...
It provides good speed control.
Second-degree burn.
Capacitance.
Draw less current.

17. At what rate should mouth-to-mouth resuscitation be applied?
Tied together
Inductance.
12 to 15 times a minute.
150 turns.

18. A transformer with a 1:1 ratio is usually a (an)...
5:1
Carotid pulse - which is located in the neck next to the Adam's apple.
X.
Isolation transformer.

19. The combined capacitance of two capacitors in parallel is...
60 cycles per second (60 Hertz).
3 -979 Volts.
The sum of the two capacitors.
Short-circuited after power has been removed.

20. What steps up or steps down AC voltage?
At the source transformer.
Circuit Breaker.
Capacitance.
Transformer

21. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Isolation transformer.
The chest should rise or inflate.
Inductance.
The sum of the two capacitors.

22. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Reverse any two-phase leads.
15 feet off the ground.
7 -630 volts.
Four times less than that of the secondary.

23. What type of 3-phase AC motor is used most often around a mine?
Stator windings.
The capacitors should be discharged.
Reverse its rotation.
Squirrel-cage induction motor.

24. Define alternating current...
Squirrel-cage induction motor.
3 -979 Volts.
Current changing constantly in magnitude and periodically in direction.
Cut around clothing that has adhered to the burned area.

25. Not a symptom of electrical shock?.
The sum of the two capacitors.
Capacitance.
Hyperventilation.
Current changing constantly in magnitude and periodically in direction.

26. A wound-rotor induction motor has all the following EXCEPT...
150 turns.
Transformers.
Squirrel-cage rotor.
No.6 AWG.

27. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Capacitance.
600 volts.
Two speeds
X.

28. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
Lower current and higher voltage
Disconnect the frame-grounding conductor.
Tied together

29. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Continuous.
Draw less current.
277 volts.

30. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Cut around clothing that has adhered to the burned area.
Two speeds
No.6 AWG.
Carotid pulse - which is located in the neck next to the Adam's apple.

31. A solenoid coil is...
An electromagnet.
Current that changes constantly in magnitude and periodically in direction.
600 volts.
3 -979 Volts.

32. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Stator windings.
Tied together
7 -630 volts.
Short-circuited after power has been removed.

33. Not true about AC power?
A step-up transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
25 feet.
It provides good speed control.

34. Compared to the secondary of a loaded - step-down transformer - the primary has...
60 Hertz
Lower current and higher voltage.
Lower current and higher voltage
480 volts.

35. The primary function of a power transformer is to provide...
Stator windings.
Full-load - three-phase voltage.
Draw less current.
The chest should rise or inflate.

36. To protect against over-current in a three-phase circuit over-current protection must be provided for...
H terminals.
At least two phases
Circuit Breaker.
At the source transformer.

37. What is the danger when working around capacitors?
Clamp-on ammeter.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
An electrical shock hazard may exist.
Isolation transformer.

38. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
Full-load - three-phase voltage.
Check to make sure that the victim is not still in contact with the electricity.
Grounded phase and ground fault devices were not operating.

39. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Reverse its rotation.
5:1.
It provides good speed control.

40. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Squirrel-cage induction motor.
Stator windings.
5:1.
15 feet off the ground.

41. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
A device used to store electrical energy.
Check to make sure that the victim is not still in contact with the electricity.
A.C.

42. The standard frequency of power supplied by the power company is...
An electrical shock hazard may exist.
480 volts.
800 volts.
60 cycles per second (60 Hertz).

43. Operating coils - motors - transformers - relays and solenoids depend upon...
X.
Electro-magnetism for their operation.
The motor rotation is reversed.
Transformer

44. Where should grounding resistors be located?
60 Hertz
Current that changes constantly in magnitude and periodically in direction.
Four times less than that of the secondary.
At the source transformer.

45. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
15 feet off the ground.
Continuous.
25 feet.
Disconnect the frame-grounding conductor.

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

47. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The motor rotation is reversed.
Transformers.
Two speeds
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

48. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
75 turns.
15 feet off the ground.
1 amp.
7 -630 volts.

49. The main function of CT's and PT's on a main substation is to...
The capacitors should be discharged.
Allow for metering voltage and Current.
At the source transformer.
Transformer

50. The standard frequency of alternating current used at a mine is...
Capacitance.
An electrical shock hazard may exist.
60 Hertz
60 cycles per second (60 Hertz).