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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. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
200 volts AC.
600 volts.
X.
Hyperventilation.

2. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
The current will read zero.
75 turns.
100 turns.

3. A control power transformer...
2000 watts
It provides good speed control.
Shunted and taped
Provides single-phase power to smaller loads such as lights - heaters - etc.

4. The primary leads of a single-phase transformer should be connected to the...
H terminals.
Reverse its rotation.
Lower current and higher voltage.
Hyperventilation.

5. 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.
The motor rotation is reversed.
Zero amps.
Derive a neutral for grounding purposes.
5:1

6. Current in an AC circuit may be measured by...
It provides good speed control.
Kilovolt ampere (KVA).
They must be installed at least 7 feet above the ground.
Clamp-on ammeter.

7. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Clamp-on ammeter.
Four times less than that of the secondary.
Capacitance.
They should be made by the same manufacturer.

8. A solenoid coil is...
The current will read zero.
An electromagnet.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Derive a neutral for grounding purposes.

9. 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...
Transformers.
Cut around clothing that has adhered to the burned area.
Draw less current.
Lower current and higher voltage.

10. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
277 volts.
2000 watts
A step-up transformer.
An electromagnet.

11. 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?
No.6 AWG.
Stator windings.
100 turns.
At least two phases

12. 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?
Clamp-on ammeter.
800 volts.
Squirrel-cage induction motor.
75 turns.

13. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
A device used to store electrical energy.
Lower current and higher voltage
Kilovolt ampere (KVA).

14. The combined capacitance of two capacitors in parallel is...
Kilovolt ampere (KVA).
At the source transformer.
The sum of the two capacitors.
3 -979 Volts.

15. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
75 turns.
An electromagnet.
The current will read zero.
A grounding resistor.

16. Current that changes periodically in direction is...
They must be installed at least 7 feet above the ground.
At least two phases
Alternating current.
Draw less current.

17. High voltage is used to transmit power over long distances...
Hyperventilation.
It provides good speed control.
Electro-magnetism for their operation.
Because less current flowing at high voltage causes less line loss per kilowatt.

18. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Current that changes constantly in magnitude and periodically in direction.
Carotid pulse - which is located in the neck next to the Adam's apple.
At the source transformer.
Zero amps.

19. At what rate should mouth-to-mouth resuscitation be applied?
Nearly constant.
The motor rotation is reversed.
1 amp.
12 to 15 times a minute.

20. 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?
15 feet off the ground.
Two speeds
75 turns.
At least two phases

21. Where should grounding resistors be located?
At the source transformer.
Current changing constantly in magnitude and periodically in direction.
Larger than that found in the primary winding.
They must be installed at least 7 feet above the ground.

22. The transformer used only to measure voltage is a...
Potential transformer.
Carotid pulse - which is located in the neck next to the Adam's apple.
Alternating current.
Squirrel-cage rotor.

23. 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 motor rotation is reversed.
Provides single-phase power to smaller loads such as lights - heaters - etc.
2000 watts

24. The size of a transformer is measured in...
No.6 AWG.
Kilovolt ampere (KVA).
Current that changes constantly in magnitude and periodically in direction.
800 volts.

25. Define alternating current...
A step-up transformer.
Continuous.
Current changing constantly in magnitude and periodically in direction.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

26. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
75 turns.
2000 watts
Larger than that found in the primary winding.
Two speeds

27. 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?
Potential transformer.
800 volts.
Lower current and higher voltage
Inductance.

28. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
600 volts.
277 volts.
Transformers.
Tied together

29. Not true about AC power?
H terminals.
At the source transformer.
It provides good speed control.
Stator windings.

30. What type of 3-phase AC motor is used most often around a mine?
Disconnect the frame-grounding conductor.
60 cycles per second (60 Hertz).
Squirrel-cage induction motor.
Because less current flowing at high voltage causes less line loss per kilowatt.

31. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
60 Hertz
15 feet off the ground.
Allow for metering voltage and Current.
Cut around clothing that has adhered to the burned area.

32. 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.
Potential transformer.
Two speeds
They must be installed at least 7 feet above the ground.
5:1.

33. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Second-degree burn.
1 amp.
Provides single-phase power to smaller loads such as lights - heaters - etc.
7 -630 volts.

34. Which of the following does a squirrel cage induction motor have?
Nearly constant.
Two speeds
Tied together
Stator windings.

35. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
75 turns.
60 Hertz
The motor rotation is reversed.

36. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
100 volts.
7 -630 volts.
The motor rotation is reversed.

37. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
A step-up transformer.
An electrical shock hazard may exist.
Tied together
25 feet.

38. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Carotid pulse - which is located in the neck next to the Adam's apple.
150 turns.
No.6 AWG.
At least two phases

39. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
Kilovolt ampere (KVA).
75 turns.
Provides single-phase power to smaller loads such as lights - heaters - etc.

40. When not connected to a load - the secondary leads of a current transformer should be...
Carotid pulse - which is located in the neck next to the Adam's apple.
25 feet.
A grounding resistor.
Shunted and taped

41. 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.
5:1
150 turns.
The current will read zero.

42. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
The motor rotation is reversed.
X.
Squirrel-cage rotor.

43. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
60 cycles per second (60 Hertz).
Larger than that found in the primary winding.
Cut around clothing that has adhered to the burned area.

44. 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...
Isolation transformer.
Carotid pulse - which is located in the neck next to the Adam's apple.
Grounded phase and ground fault devices were not operating.
100 volts.

45. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
Clamp-on ammeter.
Grounded phase and ground fault devices were not operating.
60 cycles per second (60 Hertz).

46. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Two speeds
277 volts.
480 volts.
Short-circuited after power has been removed.

47. If any two-phase wires are reversed on a three-phase motor - the motor will...
The chest should rise or inflate.
Squirrel-cage rotor.
Reverse any two-phase leads.
Reverse its rotation.

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

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49. 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?
Nearly constant.
600 volts.
Potential transformer.
3 -979 Volts.

50. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Hyperventilation.
25 feet.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Continuous.