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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 current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
X.
Draw less current.
1 amp.
The chest should rise or inflate.

2. What type of 3-phase AC motor is used most often around a mine?
Transformer
Squirrel-cage induction motor.
X.
At least two phases

3. What is a capacitor?
Grounded phase and ground fault devices were not operating.
200 volts AC.
A device used to store electrical energy.
Full-load - three-phase voltage.

4. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Disconnect the frame-grounding conductor.
Transformer
Grounded phase and ground fault devices were not operating.
25 feet.

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

6. A control power transformer...
Shunted and taped
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
An electromagnet.
Provides single-phase power to smaller loads such as lights - heaters - etc.

7. A wound-rotor induction motor has all the following EXCEPT...
5:1
Squirrel-cage rotor.
An electromagnet.
Lower current and higher voltage.

8. Current in an AC circuit may be measured by...
The chest should rise or inflate.
Clamp-on ammeter.
Isolation transformer.
Continuous.

9. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
A grounding resistor.
Isolation transformer.
Full-load - three-phase voltage.
The current will read zero.

10. 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?
They must be installed at least 7 feet above the ground.
Transformer
3 -979 Volts.
Check to make sure that the victim is not still in contact with the electricity.

11. High voltage is used to transmit power over long distances...
5:1.
Because less current flowing at high voltage causes less line loss per kilowatt.
3 -979 Volts.
25 feet.

12. 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?
An electrical shock hazard may exist.
800 volts.
75 turns.
25 feet.

13. All transformers step voltage up or down by...
200 volts AC.
Grounded phase and ground fault devices were not operating.
At least two phases
Inductance.

14. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
480 volts.
Potential transformer.
60 Hertz
X.

15. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
At least two phases
Circuit Breaker.
Disconnect the frame-grounding conductor.

16. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
At least two phases
The chest should rise or inflate.
Nearly constant.
Allow for metering voltage and Current.

17. The primary function of a power transformer is to provide...
At least two phases
Tied together
No.6 AWG.
Full-load - three-phase voltage.

18. The purpose of a zig-zag transformer is to...
75 turns.
Derive a neutral for grounding purposes.
800 volts.
Stator windings.

19. 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...
15 feet off the ground.
No.6 AWG.
100 volts.
150 turns.

20. 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?
25 feet.
75 turns.
150 turns.
Derive a neutral for grounding purposes.

21. The combined capacitance of two capacitors in parallel is...
An electromagnet.
Cut around clothing that has adhered to the burned area.
75 turns.
The sum of the two capacitors.

22. A burn causing a blister is classified as a...
Second-degree burn.
Draw less current.
Reverse its rotation.
1 amp.

23. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
H terminals.
Short-circuited after power has been removed.
X.
25 feet.

24. The standard frequency of alternating current used at a mine is...
60 Hertz
Draw less current.
Zero amps.
Shunted and taped

25. 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.
Squirrel-cage rotor.
Capacitance.
Draw less current.

26. The primary leads of a single-phase transformer should be connected to the...
Capacitance.
100 turns.
H terminals.
The current will read zero.

27. What type motor is a wound-rotor induction motor?
The current will read zero.
Stator windings.
A.C.
100 turns.

28. Current that changes periodically in direction is...
3 -979 Volts.
Alternating current.
Short-circuited after power has been removed.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

29. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Four times less than that of the secondary.
Transformer
7 -630 volts.
75 turns.

30. The property of an electrical circuit that opposes any change in voltage is called...
600 volts.
Capacitance.
Squirrel-cage induction motor.
Hyperventilation.

31. 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...
Inductance.
Transformers.
Draw less current.
An electromagnet.

32. The property of an electric circuit that opposes any change in current is called...
Inductance.
Because less current flowing at high voltage causes less line loss per kilowatt.
It provides good speed control.
3 -979 Volts.

33. When not connected to a load - the secondary leads of a current transformer should be...
75 turns.
Inductance.
Shunted and taped
60 cycles per second (60 Hertz).

34. The transformer used only to measure voltage is a...
100 volts.
12 to 15 times a minute.
Potential transformer.
Two speeds

35. A solenoid coil is...
Alternating current.
Reverse its rotation.
An electromagnet.
Draw less current.

36. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
Current changing constantly in magnitude and periodically in direction.
60 cycles per second (60 Hertz).
277 volts.

37. 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.
H terminals.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
100 volts.

38. Alternating current may be defined as...
They should be made by the same manufacturer.
60 Hertz
Current that changes constantly in magnitude and periodically in direction.
Transformer

39. The standard frequency of power supplied by the power company is...
100 volts.
Clamp-on ammeter.
60 cycles per second (60 Hertz).
600 volts.

40. 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...
A device used to store electrical energy.
Derive a neutral for grounding purposes.
200 volts AC.
Tied together

41. 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?
Hyperventilation.
The sum of the two capacitors.
Capacitance.
100 turns.

42. The secondary windings on a 10:1 step-down transformer will have a wire size...
Second-degree burn.
Larger than that found in the primary winding.
No.6 AWG.
It provides good speed control.

43. 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.
Provides single-phase power to smaller loads such as lights - heaters - etc.
They must be installed at least 7 feet above the ground.
5:1
Inductance.

44. Which of the following does a squirrel cage induction motor have?
Stator windings.
Alternating current.
Reverse any two-phase leads.
Lower current and higher voltage.

45. 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.
75 turns.
They should be made by the same manufacturer.
Capacitance.

46. What should the duty rating of a grounding resistor be?
A.C.
Continuous.
Disconnect the frame-grounding conductor.
X.

47. Not a symptom of electrical shock?.
Lower current and higher voltage.
3 -979 Volts.
Hyperventilation.
Kilovolt ampere (KVA).

48. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Reverse its rotation.
Inductance.
It provides good speed control.
7 -630 volts.

49. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
75 turns.
Circuit Breaker.
Lower current and higher voltage.
25 feet.

50. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
5:1
At least two phases
480 volts.
H terminals.