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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 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?
Lower current and higher voltage.
Carotid pulse - which is located in the neck next to the Adam's apple.
800 volts.
75 turns.

2. 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.
Draw less current.
Cut around clothing that has adhered to the burned area.
The chest should rise or inflate.

3. The property of an electric circuit that opposes any change in current is called...
Shunted and taped
A device used to store electrical energy.
200 volts AC.
Inductance.

4. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Lower current and higher voltage
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
5:1
Check to make sure that the victim is not still in contact with the electricity.

5. 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
Shunted and taped
Capacitance.
An electromagnet.

6. The standard frequency of alternating current used at a mine is...
60 Hertz
The capacitors should be discharged.
X.
1 amp.

7. What is a capacitor?
100 turns.
75 turns.
A device used to store electrical energy.
Zero amps.

8. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Grounded phase and ground fault devices were not operating.
A.C.
Circuit Breaker.
Draw less current.

9. Three-phase AC underground cables must be provided with overcurrent protection using a...
H terminals.
Circuit Breaker.
Cut around clothing that has adhered to the burned area.
25 feet.

10. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Current changing constantly in magnitude and periodically in direction.
Circuit Breaker.
1 amp.
Check to make sure that the victim is not still in contact with the electricity.

11. The standard frequency of power supplied by the power company is...
They should be made by the same manufacturer.
60 cycles per second (60 Hertz).
75 turns.
The current will read zero.

12. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
No.6 AWG.
Current changing constantly in magnitude and periodically in direction.
Current that changes constantly in magnitude and periodically in direction.
25 feet.

13. Which of the following does a squirrel cage induction motor have?
They must be installed at least 7 feet above the ground.
Stator windings.
12 to 15 times a minute.
5:1.

14. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Cut around clothing that has adhered to the burned area.
Hyperventilation.
Because less current flowing at high voltage causes less line loss per kilowatt.

15. What type motor is a wound-rotor induction motor?
The sum of the two capacitors.
A.C.
Inductance.
X.

16. 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?
277 volts.
At least two phases
100 turns.
75 turns.

17. The transformer used only to measure voltage is a...
Potential transformer.
Electro-magnetism for their operation.
Circuit Breaker.
60 Hertz

18. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The capacitors should be discharged.
At the source transformer.
It provides good speed control.

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

20. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Full-load - three-phase voltage.
Four times less than that of the secondary.
The capacitors should be discharged.

21. The speed of an alternating current - squirrel-cage induction motor is...
Transformer
Nearly constant.
The capacitors should be discharged.
Grounded phase and ground fault devices were not operating.

22. A burn causing a blister is classified as a...
Zero amps.
The chest should rise or inflate.
Second-degree burn.
75 turns.

23. At what rate should mouth-to-mouth resuscitation be applied?
Full-load - three-phase voltage.
12 to 15 times a minute.
A.C.
Two speeds

24. 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?
3 -979 Volts.
They must be installed at least 7 feet above the ground.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
15 feet off the ground.

25. The purpose of a zig-zag transformer is to...
Isolation transformer.
The sum of the two capacitors.
Derive a neutral for grounding purposes.
Two speeds

26. 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.
A.C.
5:1
200 volts AC.
12 to 15 times a minute.

27. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
200 volts AC.
2000 watts
Carotid pulse - which is located in the neck next to the Adam's apple.

28. Operating coils - motors - transformers - relays and solenoids depend upon...
Current that changes constantly in magnitude and periodically in direction.
Larger than that found in the primary winding.
5:1
Electro-magnetism for their operation.

29. How do you change the direction of a 3-phase AC motor?
Transformers.
Reverse any two-phase leads.
They should be made by the same manufacturer.
The motor rotation is reversed.

30. 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?
The current will read zero.
75 turns.
X.
The chest should rise or inflate.

31. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
They must be installed at least 7 feet above the ground.
800 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.

32. Not a symptom of electrical shock?.
Hyperventilation.
600 volts.
60 Hertz
800 volts.

33. 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.
Second-degree burn.
Carotid pulse - which is located in the neck next to the Adam's apple.

34. The secondary windings on a 10:1 step-down transformer will have a wire size...
100 turns.
Larger than that found in the primary winding.
3 -979 Volts.
Zero amps.

35. 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?
150 turns.
200 volts AC.
Potential transformer.
277 volts.

36. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
150 turns.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Two speeds
100 volts.

37. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
The chest should rise or inflate.
Four times less than that of the secondary.
No.6 AWG.

38. Compared to the secondary of a loaded - step-down transformer - the primary has...
Circuit Breaker.
Lower current and higher voltage
The current will read zero.
Potential transformer.

39. Current transformers - or CT's - are used to...
No.6 AWG.
Zero amps.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Electro-magnetism for their operation.

40. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
277 volts.
A.C.
Shunted and taped
A step-up transformer.

41. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Reverse any two-phase leads.
Four times less than that of the secondary.
Current that changes constantly in magnitude and periodically in direction.
75 turns.

42. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Alternating current.
Squirrel-cage induction motor.
The capacitors should be discharged.

43. A solenoid coil is...
3 -979 Volts.
An electromagnet.
Capacitance.
The motor rotation is reversed.

44. Alternating current may be defined as...
2000 watts
Current that changes constantly in magnitude and periodically in direction.
12 to 15 times a minute.
Disconnect the frame-grounding conductor.

45. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Kilovolt ampere (KVA).
Because less current flowing at high voltage causes less line loss per kilowatt.
A grounding resistor.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

46. When not connected to a load - the secondary leads of a current transformer should be...
Disconnect the frame-grounding conductor.
Shunted and taped
Two speeds
Current changing constantly in magnitude and periodically in direction.

47. High voltage is used to transmit power over long distances...
Capacitance.
The current will read zero.
Because less current flowing at high voltage causes less line loss per kilowatt.
5:1

48. Current in an AC circuit may be measured by...
An electrical shock hazard may exist.
800 volts.
Draw less current.
Clamp-on ammeter.

49. 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...
The capacitors should be discharged.
Draw less current.
H terminals.
480 volts.

50. What should the duty rating of a grounding resistor be?
60 cycles per second (60 Hertz).
An electrical shock hazard may exist.
Continuous.
5:1