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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. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
Transformers.
25 feet.
A step-up transformer.

2. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
60 Hertz
Check to make sure that the victim is not still in contact with the electricity.
At the source transformer.

3. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
They must be installed at least 7 feet above the ground.
600 volts.
Tied together

4. 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
75 turns.
Draw less current.
The capacitors should be discharged.

5. 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...
Because less current flowing at high voltage causes less line loss per kilowatt.
Draw less current.
150 turns.
The chest should rise or inflate.

6. Alternating current may be defined as...
150 turns.
480 volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Current that changes constantly in magnitude and periodically in direction.

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

8. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
A device used to store electrical energy.
Grounded phase and ground fault devices were not operating.
Clamp-on ammeter.
7 -630 volts.

9. Not a symptom of electrical shock?.
100 volts.
Hyperventilation.
5:1.
Lower current and higher voltage

10. 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...
600 volts.
Isolation transformer.
100 volts.
No.6 AWG.

11. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
75 turns.
Reverse any two-phase leads.
277 volts.
Cut around clothing that has adhered to the burned area.

12. High voltage is used to transmit power over long distances...
The current will read zero.
Current changing constantly in magnitude and periodically in direction.
Because less current flowing at high voltage causes less line loss per kilowatt.
Isolation transformer.

13. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Cut around clothing that has adhered to the burned area.
Squirrel-cage rotor.
60 cycles per second (60 Hertz).

14. A wound-rotor induction motor has all the following EXCEPT...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
X.
600 volts.
Squirrel-cage rotor.

15. The combined capacitance of two capacitors in parallel is...
75 turns.
Squirrel-cage rotor.
Cut around clothing that has adhered to the burned area.
The sum of the two capacitors.

16. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Nearly constant.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Reverse its rotation.
1 amp.

17. A burn causing a blister is classified as a...
75 turns.
Stator windings.
Tied together
Second-degree burn.

18. What is a capacitor?
A device used to store electrical energy.
Grounded phase and ground fault devices were not operating.
The motor rotation is reversed.
The sum of the two capacitors.

19. How do you change the direction of a 3-phase AC motor?
Kilovolt ampere (KVA).
Alternating current.
Reverse any two-phase leads.
600 volts.

20. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Lower current and higher voltage.
Four times less than that of the secondary.
Zero amps.
The current will read zero.

21. Three-phase AC underground cables must be provided with overcurrent protection using a...
Draw less current.
Circuit Breaker.
Shunted and taped
No.6 AWG.

22. 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?
Electro-magnetism for their operation.
800 volts.
Zero amps.
7 -630 volts.

23. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Derive a neutral for grounding purposes.
480 volts.
Second-degree burn.
Disconnect the frame-grounding conductor.

24. Compared to the secondary of a loaded - step-down transformer - the primary has...
Nearly constant.
25 feet.
480 volts.
Lower current and higher voltage.

25. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Inductance.
1 amp.
7 -630 volts.
Check to make sure that the victim is not still in contact with the electricity.

26. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
Short-circuited after power has been removed.
100 volts.
The capacitors should be discharged.

27. What is the danger when working around capacitors?
Squirrel-cage induction motor.
200 volts AC.
X.
An electrical shock hazard may exist.

28. If any two-phase wires are reversed on a three-phase motor - the motor will...
Transformers.
200 volts AC.
Reverse its rotation.
Kilovolt ampere (KVA).

29. Current in an AC circuit may be measured by...
Two speeds
Zero amps.
Clamp-on ammeter.
Because less current flowing at high voltage causes less line loss per kilowatt.

30. The standard frequency of power supplied by the power company is...
The capacitors should be discharged.
Zero amps.
Inductance.
60 cycles per second (60 Hertz).

31. Not true about AC power?
100 turns.
It provides good speed control.
1 amp.
Check to make sure that the victim is not still in contact with the electricity.

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.
Electro-magnetism for their operation.
It provides good speed control.
5:1.
75 turns.

33. What type of 3-phase AC motor is used most often around a mine?
Nearly constant.
Squirrel-cage induction motor.
Two speeds
25 feet.

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

35. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Check to make sure that the victim is not still in contact with the electricity.
800 volts.
The current will read zero.
The motor rotation is reversed.

36. Current that changes periodically in direction is...
Zero amps.
Alternating current.
A grounding resistor.
Full-load - three-phase voltage.

37. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
15 feet off the ground.
Stator windings.
The chest should rise or inflate.
Inductance.

38. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
Disconnect the frame-grounding conductor.
Reverse its rotation.
A.C.

39. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
600 volts.
The current will read zero.
They should be made by the same manufacturer.
It provides good speed control.

40. 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.
Four times less than that of the secondary.
3 -979 Volts.
Inductance.

41. 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?
15 feet off the ground.
The motor rotation is reversed.
An electrical shock hazard may exist.
600 volts.

42. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
A grounding resistor.
Lower current and higher voltage.
Zero amps.

43. The primary leads of a single-phase transformer should be connected to the...
The motor rotation is reversed.
H terminals.
Squirrel-cage rotor.
277 volts.

44. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
3 -979 Volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Full-load - three-phase voltage.

45. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Lower current and higher voltage
Tied together
2000 watts
A grounding resistor.

46. At what rate should mouth-to-mouth resuscitation be applied?
Grounded phase and ground fault devices were not operating.
12 to 15 times a minute.
A grounding resistor.
At the source transformer.

47. 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?
Zero amps.
150 turns.
Draw less current.
12 to 15 times a minute.

48. 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.
No.6 AWG.
An electrical shock hazard may exist.
Reverse any two-phase leads.

49. The standard frequency of alternating current used at a mine is...
600 volts.
100 volts.
Potential transformer.
60 Hertz

50. The transformer used only to measure voltage is a...
Transformers.
Continuous.
Shunted and taped
Potential transformer.