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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 1 -600 turns in the primary and 400 turns in the secondary. The primary voltage is 2 -400 volts. What is the secondary voltage?
Alternating current.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
600 volts.
Two speeds

2. The standard frequency of power supplied by the power company is...
Inductance.
15 feet off the ground.
7 -630 volts.
60 cycles per second (60 Hertz).

3. Current transformers - or CT's - are used to...
No.6 AWG.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Larger than that found in the primary winding.
Because less current flowing at high voltage causes less line loss per kilowatt.

4. 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.
It provides good speed control.
Zero amps.
No.6 AWG.

5. Not true about AC power?
Continuous.
2000 watts
It provides good speed control.
800 volts.

6. What is the first step to be followed in aiding a victim of electrical shock?
Hyperventilation.
Circuit Breaker.
The current will read zero.
Check to make sure that the victim is not still in contact with the electricity.

7. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Zero amps.
Isolation transformer.
15 feet off the ground.
They should be made by the same manufacturer.

8. 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...
H terminals.
Draw less current.
X.
At the source transformer.

9. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Lower current and higher voltage.
277 volts.
150 turns.
Squirrel-cage rotor.

10. What type motor is a wound-rotor induction motor?
Shunted and taped
H terminals.
800 volts.
A.C.

11. Operating coils - motors - transformers - relays and solenoids depend upon...
Nearly constant.
Electro-magnetism for their operation.
A.C.
Draw less current.

12. The property of an electric circuit that opposes any change in current is called...
Inductance.
The sum of the two capacitors.
Carotid pulse - which is located in the neck next to the Adam's apple.
Current that changes constantly in magnitude and periodically in direction.

13. 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.
75 turns.
5:1.
Shunted and taped
Transformers.

14. A transformer with a 1:1 ratio is usually a (an)...
A.C.
Transformers.
Disconnect the frame-grounding conductor.
Isolation transformer.

15. Where should grounding resistors be located?
Circuit Breaker.
At the source transformer.
2000 watts
25 feet.

16. 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.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Provides single-phase power to smaller loads such as lights - heaters - etc.
A.C.

17. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Alternating current.
Provides single-phase power to smaller loads such as lights - heaters - etc.
100 turns.
The chest should rise or inflate.

18. Current in an AC circuit may be measured by...
Continuous.
An electromagnet.
Potential transformer.
Clamp-on ammeter.

19. The combined capacitance of two capacitors in parallel is...
75 turns.
The sum of the two capacitors.
A step-up transformer.
Cut around clothing that has adhered to the burned area.

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?
Derive a neutral for grounding purposes.
5:1
Inductance.
75 turns.

21. The property of an electrical circuit that opposes any change in voltage is called...
The capacitors should be discharged.
A.C.
Capacitance.
The chest should rise or inflate.

22. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
Potential transformer.
Larger than that found in the primary winding.
Reverse its rotation.

23. What is a capacitor?
Transformer
Carotid pulse - which is located in the neck next to the Adam's apple.
Second-degree burn.
A device used to store electrical energy.

24. Which of the following does a squirrel cage induction motor have?
Draw less current.
Current changing constantly in magnitude and periodically in direction.
75 turns.
Stator windings.

25. Three-phase AC underground cables must be provided with overcurrent protection using a...
Reverse its rotation.
Stator windings.
Circuit Breaker.
Carotid pulse - which is located in the neck next to the Adam's apple.

26. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Larger than that found in the primary winding.
No.6 AWG.
The sum of the two capacitors.
The capacitors should be discharged.

27. When not connected to a load - the secondary leads of a current transformer should be...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Shunted and taped
2000 watts
277 volts.

28. 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?
Draw less current.
A step-up transformer.
The chest should rise or inflate.
800 volts.

29. AC voltage is raised or lowered by means of...
Derive a neutral for grounding purposes.
Transformers.
They should be made by the same manufacturer.
Lower current and higher voltage

30. What is the danger when working around capacitors?
No.6 AWG.
200 volts AC.
An electrical shock hazard may exist.
The chest should rise or inflate.

31. A solenoid coil is...
25 feet.
An electromagnet.
Continuous.
Circuit Breaker.

32. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Inductance.
Four times less than that of the secondary.
Allow for metering voltage and Current.
Capacitance.

33. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Grounded phase and ground fault devices were not operating.
No.6 AWG.
An electrical shock hazard may exist.
A grounding resistor.

34. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
150 turns.
Lower current and higher voltage
7 -630 volts.
It provides good speed control.

35. Current that changes periodically in direction is...
75 turns.
Transformer
Transformers.
Alternating current.

36. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
The chest should rise or inflate.
Inductance.
No.6 AWG.
60 Hertz

37. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Electro-magnetism for their operation.
No.6 AWG.
The motor rotation is reversed.

38. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Kilovolt ampere (KVA).
Four times less than that of the secondary.
Draw less current.
The current will read zero.

39. 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...
It provides good speed control.
100 volts.
Nearly constant.
12 to 15 times a minute.

40. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
X.
Shunted and taped
The chest should rise or inflate.

41. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Disconnect the frame-grounding conductor.
60 cycles per second (60 Hertz).
100 volts.
Two speeds

42. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
The sum of the two capacitors.
Current that changes constantly in magnitude and periodically in direction.
Second-degree burn.
2000 watts

43. Alternating current may be defined as...
Shunted and taped
Continuous.
Current that changes constantly in magnitude and periodically in direction.
A step-up transformer.

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

45. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
7 -630 volts.
They should be made by the same manufacturer.
Cut around clothing that has adhered to the burned area.
Provides single-phase power to smaller loads such as lights - heaters - etc.

46. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Continuous.
Disconnect the frame-grounding conductor.
At the source transformer.
Short-circuited after power has been removed.

47. 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.
5:1.
Capacitance.
The sum of the two capacitors.
5:1

48. The primary leads of a single-phase transformer should be connected to the...
The motor rotation is reversed.
Squirrel-cage induction motor.
H terminals.
Four times less than that of the secondary.

49. At what rate should mouth-to-mouth resuscitation be applied?
Four times less than that of the secondary.
It provides good speed control.
A.C.
12 to 15 times a minute.

50. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
Circuit Breaker.
Two speeds
Draw less current.