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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. What type of 3-phase AC motor is used most often around a mine?
A step-up transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.
Squirrel-cage induction motor.
A.C.

2. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
2000 watts
A step-up transformer.
Carotid pulse - which is located in the neck next to the Adam's apple.
Circuit Breaker.

3. What is a capacitor?
A device used to store electrical energy.
Disconnect the frame-grounding conductor.
H terminals.
Current that changes constantly in magnitude and periodically in direction.

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

5. 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.
Grounded phase and ground fault devices were not operating.
Current changing constantly in magnitude and periodically in direction.
Lower current and higher voltage.

6. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Provides single-phase power to smaller loads such as lights - heaters - etc.
7 -630 volts.
Clamp-on ammeter.
Squirrel-cage rotor.

7. Alternating current may be defined as...
A grounding resistor.
Check to make sure that the victim is not still in contact with the electricity.
Current that changes constantly in magnitude and periodically in direction.
Disconnect the frame-grounding conductor.

8. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
Lower current and higher voltage.
Shunted and taped
Larger than that found in the primary winding.

9. The combined capacitance of two capacitors in parallel is...
Electro-magnetism for their operation.
3 -979 Volts.
The sum of the two capacitors.
75 turns.

10. Where should grounding resistors be located?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Inductance.
At the source transformer.
12 to 15 times a minute.

11. Not true about AC power?
It provides good speed control.
No.6 AWG.
75 turns.
A grounding resistor.

12. The primary leads of a single-phase transformer should be connected to the...
H terminals.
Potential transformer.
Short-circuited after power has been removed.
Circuit Breaker.

13. How should clothing be removed from a burn?
Potential transformer.
Continuous.
Cut around clothing that has adhered to the burned area.
Lower current and higher voltage.

14. The secondary windings on a 10:1 step-down transformer will have a wire size...
X.
Larger than that found in the primary winding.
The capacitors should be discharged.
The sum of the two capacitors.

15. The purpose of a zig-zag transformer is to...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Derive a neutral for grounding purposes.
800 volts.
150 turns.

16. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
An electromagnet.
800 volts.
25 feet.

17. 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.
Short-circuited after power has been removed.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Squirrel-cage induction motor.

18. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
277 volts.
Clamp-on ammeter.
2000 watts
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

19. The transformer used only to measure voltage is a...
Potential transformer.
Short-circuited after power has been removed.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Squirrel-cage induction motor.

20. What steps up or steps down AC voltage?
480 volts.
Larger than that found in the primary winding.
Transformer
Short-circuited after power has been removed.

21. 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.
15 feet off the ground.
Electro-magnetism for their operation.
Zero amps.

22. 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...
600 volts.
Draw less current.
7 -630 volts.
The capacitors should be discharged.

23. 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?
A.C.
Current changing constantly in magnitude and periodically in direction.
800 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.

24. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
The capacitors should be discharged.
Squirrel-cage rotor.
X.
The sum of the two capacitors.

25. Current in an AC circuit may be measured by...
An electromagnet.
7 -630 volts.
12 to 15 times a minute.
Clamp-on ammeter.

26. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Allow for metering voltage and Current.
The capacitors should be discharged.
An electrical shock hazard may exist.
An electromagnet.

27. 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?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Because less current flowing at high voltage causes less line loss per kilowatt.
Squirrel-cage induction motor.
100 turns.

28. Three-phase AC underground cables must be provided with overcurrent protection using a...
75 turns.
15 feet off the ground.
Circuit Breaker.
Stator windings.

29. 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.
Hyperventilation.
Capacitance.
60 Hertz
5:1

30. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
Disconnect the frame-grounding conductor.
Alternating current.
Because less current flowing at high voltage causes less line loss per kilowatt.

31. How do you change the direction of a 3-phase AC motor?
12 to 15 times a minute.
Transformer
No.6 AWG.
Reverse any two-phase leads.

32. 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...
Lower current and higher voltage
Inductance.
100 volts.
Grounded phase and ground fault devices were not operating.

33. To protect against over-current in a three-phase circuit over-current protection must be provided for...
A step-up transformer.
At least two phases
277 volts.
Alternating current.

34. Current transformers - or CT's - are used to...
15 feet off the ground.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Transformer
5:1.

35. A wound-rotor induction motor has all the following EXCEPT...
At least two phases
They must be installed at least 7 feet above the ground.
Squirrel-cage rotor.
200 volts AC.

36. What should the duty rating of a grounding resistor be?
200 volts AC.
Continuous.
277 volts.
They must be installed at least 7 feet above the ground.

37. AC voltage is raised or lowered by means of...
Inductance.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Transformers.
Provides single-phase power to smaller loads such as lights - heaters - etc.

38. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
800 volts.
277 volts.
Isolation transformer.

39. High voltage is used to transmit power over long distances...
2000 watts
1 amp.
Because less current flowing at high voltage causes less line loss per kilowatt.
Derive a neutral for grounding purposes.

40. All transformers step voltage up or down by...
Inductance.
3 -979 Volts.
2000 watts
Kilovolt ampere (KVA).

41. What is the danger when working around capacitors?
An electrical shock hazard may exist.
Transformers.
60 cycles per second (60 Hertz).
60 Hertz

42. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
Stator windings.
Second-degree burn.
An electrical shock hazard may exist.

43. 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...
Draw less current.
Tied together
The chest should rise or inflate.
Squirrel-cage rotor.

44. A solenoid coil is...
The capacitors should be discharged.
Disconnect the frame-grounding conductor.
An electromagnet.
No.6 AWG.

45. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Second-degree burn.
75 turns.
X.
The current will read zero.

46. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
25 feet.
Cut around clothing that has adhered to the burned area.
A step-up transformer.
Carotid pulse - which is located in the neck next to the Adam's apple.

47. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Full-load - three-phase voltage.
12 to 15 times a minute.
Allow for metering voltage and Current.

48. 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?
600 volts.
The capacitors should be discharged.
150 turns.
Zero amps.

49. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Lower current and higher voltage.
15 feet off the ground.
Carotid pulse - which is located in the neck next to the Adam's apple.

50. 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.
Squirrel-cage induction motor.
5:1.
3 -979 Volts.