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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. Not true about AC power?
Current changing constantly in magnitude and periodically in direction.
An electromagnet.
The motor rotation is reversed.
It provides good speed control.

2. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Alternating current.
277 volts.
Transformer
1 amp.

3. 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.
No.6 AWG.
Transformer
Draw less current.
5:1

4. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Reverse any two-phase leads.
3 -979 Volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

5. 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?
Two speeds
Squirrel-cage rotor.
Stator windings.
600 volts.

6. Current in an AC circuit may be measured by...
Squirrel-cage rotor.
Clamp-on ammeter.
15 feet off the ground.
Circuit Breaker.

7. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Squirrel-cage induction motor.
Alternating current.
7 -630 volts.
100 turns.

8. Operating coils - motors - transformers - relays and solenoids depend upon...
1 amp.
Electro-magnetism for their operation.
Grounded phase and ground fault devices were not operating.
Current that changes constantly in magnitude and periodically in direction.

9. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A grounding resistor.
Provides single-phase power to smaller loads such as lights - heaters - etc.
The chest should rise or inflate.
It provides good speed control.

10. Which of the following does a squirrel cage induction motor have?
Isolation transformer.
1 amp.
Potential transformer.
Stator windings.

11. What is the danger when working around capacitors?
480 volts.
An electrical shock hazard may exist.
150 turns.
277 volts.

12. A control power transformer...
Inductance.
3 -979 Volts.
Disconnect the frame-grounding conductor.
Provides single-phase power to smaller loads such as lights - heaters - etc.

13. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
Four times less than that of the secondary.
Second-degree burn.
60 Hertz

14. 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.
Alternating current.
Current changing constantly in magnitude and periodically in direction.
Inductance.

15. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
15 feet off the ground.
75 turns.
60 Hertz
Two speeds

16. Three-phase AC underground cables must be provided with overcurrent protection using a...
1 amp.
Because less current flowing at high voltage causes less line loss per kilowatt.
100 turns.
Circuit Breaker.

17. The transformer used only to measure voltage is a...
A step-up transformer.
The motor rotation is reversed.
Potential transformer.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

18. What type motor is a wound-rotor induction motor?
150 turns.
They should be made by the same manufacturer.
Transformers.
A.C.

19. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Cut around clothing that has adhered to the burned area.
Hyperventilation.
5:1.

20. How should clothing be removed from a burn?
An electrical shock hazard may exist.
200 volts AC.
Cut around clothing that has adhered to the burned area.
They must be installed at least 7 feet above the ground.

21. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Full-load - three-phase voltage.
Reverse any two-phase leads.
No.6 AWG.
2000 watts

22. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Clamp-on ammeter.
480 volts.
Second-degree burn.
The capacitors should be discharged.

23. Not a symptom of electrical shock?.
Transformers.
It provides good speed control.
Reverse its rotation.
Hyperventilation.

24. 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.
60 cycles per second (60 Hertz).
100 volts.

25. 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.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Reverse any two-phase leads.
An electromagnet.

26. 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.
100 turns.
They should be made by the same manufacturer.

27. 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?
Lower current and higher voltage
150 turns.
Draw less current.
Clamp-on ammeter.

28. What type of 3-phase AC motor is used most often around a mine?
Derive a neutral for grounding purposes.
Squirrel-cage induction motor.
Continuous.
Reverse any two-phase leads.

29. 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...
25 feet.
The motor rotation is reversed.
At least two phases
100 volts.

30. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
100 turns.
Larger than that found in the primary winding.
Zero amps.
Reverse its rotation.

31. The secondary windings on a 10:1 step-down transformer will have a wire size...
Check to make sure that the victim is not still in contact with the electricity.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
12 to 15 times a minute.
Larger than that found in the primary winding.

32. When not connected to a load - the secondary leads of a current transformer should be...
Transformer
Transformers.
100 volts.
Shunted and taped

33. 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.
277 volts.
Clamp-on ammeter.
60 cycles per second (60 Hertz).

34. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
Short-circuited after power has been removed.
480 volts.
600 volts.

35. 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.
An electromagnet.
The current will read zero.
Isolation transformer.

36. 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?
75 turns.
800 volts.
200 volts AC.
5:1.

37. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
They must be installed at least 7 feet above the ground.
X.
Transformers.
Potential transformer.

38. The speed of an alternating current - squirrel-cage induction motor is...
A.C.
Nearly constant.
Draw less current.
Potential transformer.

39. 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.
Carotid pulse - which is located in the neck next to the Adam's apple.
1 amp.
Transformer
5:1.

40. At what rate should mouth-to-mouth resuscitation be applied?
Reverse its rotation.
12 to 15 times a minute.
75 turns.
The sum of the two capacitors.

41. How do you change the direction of a 3-phase AC motor?
7 -630 volts.
Reverse any two-phase leads.
Hyperventilation.
Kilovolt ampere (KVA).

42. Current that changes periodically in direction is...
Alternating current.
Because less current flowing at high voltage causes less line loss per kilowatt.
800 volts.
Allow for metering voltage and Current.

43. The property of an electric circuit that opposes any change in current is called...
3 -979 Volts.
Capacitance.
Squirrel-cage rotor.
Inductance.

44. 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.
The chest should rise or inflate.
3 -979 Volts.
A device used to store electrical energy.

45. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
150 turns.
Draw less current.
The chest should rise or inflate.

46. All transformers step voltage up or down by...
Inductance.
At the source transformer.
The motor rotation is reversed.
Because less current flowing at high voltage causes less line loss per kilowatt.

47. 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.
25 feet.
Current changing constantly in magnitude and periodically in direction.
A step-up transformer.

48. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Current that changes constantly in magnitude and periodically in direction.
The chest should rise or inflate.
Derive a neutral for grounding purposes.

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...
Draw less current.
Cut around clothing that has adhered to the burned area.
Two speeds
It provides good speed control.

50. Compared to the secondary of a loaded - step-down transformer - the primary has...
75 turns.
Lower current and higher voltage
800 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.