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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 speed of an alternating current - squirrel-cage induction motor is...
Isolation transformer.
At the source transformer.
Nearly constant.
75 turns.

2. 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...
Isolation transformer.
Draw less current.
Reverse its rotation.
H terminals.

3. Compared to the secondary of a loaded - step-down transformer - the primary has...
Short-circuited after power has been removed.
Inductance.
Lower current and higher voltage
Tied together

4. The property of an electric circuit that opposes any change in current is called...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Squirrel-cage induction motor.
Inductance.
Transformers.

5. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Draw less current.
Four times less than that of the secondary.
The current will read zero.
Zero amps.

6. 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.
Derive a neutral for grounding purposes.
They must be installed at least 7 feet above the ground.
12 to 15 times a minute.

7. 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.
X.
Reverse any two-phase leads.
2000 watts

8. What type motor is a wound-rotor induction motor?
Lower current and higher voltage.
A.C.
600 volts.
An electrical shock hazard may exist.

9. What is the first step to be followed in aiding a victim of electrical shock?
60 Hertz
Carotid pulse - which is located in the neck next to the Adam's apple.
Shunted and taped
Check to make sure that the victim is not still in contact with the electricity.

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

11. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
15 feet off the ground.
Four times less than that of the secondary.
The sum of the two capacitors.

12. The combined capacitance of two capacitors in parallel is...
150 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.
The sum of the two capacitors.
Cut around clothing that has adhered to the burned area.

13. 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...
Transformer
Because less current flowing at high voltage causes less line loss per kilowatt.
Draw less current.
Grounded phase and ground fault devices were not operating.

14. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Four times less than that of the secondary.
Squirrel-cage rotor.
Check to make sure that the victim is not still in contact with the electricity.

15. The main function of CT's and PT's on a main substation is to...
At the source transformer.
5:1.
The chest should rise or inflate.
Allow for metering voltage and Current.

16. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
They should be made by the same manufacturer.
Carotid pulse - which is located in the neck next to the Adam's apple.
The motor rotation is reversed.
At least two phases

17. The primary leads of a single-phase transformer should be connected to the...
Tied together
5:1.
The chest should rise or inflate.
H terminals.

18. Not a symptom of electrical shock?.
100 volts.
Short-circuited after power has been removed.
Electro-magnetism for their operation.
Hyperventilation.

19. Alternating current may be defined as...
It provides good speed control.
Stator windings.
277 volts.
Current that changes constantly in magnitude and periodically in direction.

20. 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...
100 turns.
12 to 15 times a minute.
Potential transformer.
100 volts.

21. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Inductance.
Because less current flowing at high voltage causes less line loss per kilowatt.
15 feet off the ground.
A.C.

22. 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).
Short-circuited after power has been removed.
Cut around clothing that has adhered to the burned area.
The current will read zero.

23. What is the danger when working around capacitors?
An electrical shock hazard may exist.
Draw less current.
Reverse any two-phase leads.
Short-circuited after power has been removed.

24. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
H terminals.
Derive a neutral for grounding purposes.
A device used to store electrical energy.
Short-circuited after power has been removed.

25. How should clothing be removed from a burn?
75 turns.
100 turns.
Cut around clothing that has adhered to the burned area.
Larger than that found in the primary winding.

26. 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.
Four times less than that of the secondary.
Lower current and higher voltage
1 amp.
5:1.

27. What should the duty rating of a grounding resistor be?
Continuous.
A grounding resistor.
Zero amps.
Disconnect the frame-grounding conductor.

28. What steps up or steps down AC voltage?
Transformer
Larger than that found in the primary winding.
15 feet off the ground.
5:1

29. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
100 volts.
Reverse its rotation.
60 cycles per second (60 Hertz).
They should be made by the same manufacturer.

30. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
Circuit Breaker.
5:1.
Capacitance.

31. A transformer with a 1:1 ratio is usually a (an)...
Stator windings.
Isolation transformer.
Hyperventilation.
Disconnect the frame-grounding conductor.

32. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
277 volts.
200 volts AC.
Electro-magnetism for their operation.
Provides single-phase power to smaller loads such as lights - heaters - etc.

33. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Continuous.
1 amp.
Draw less current.
Lower current and higher voltage

34. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Squirrel-cage induction motor.
15 feet off the ground.
Carotid pulse - which is located in the neck next to the Adam's apple.

35. 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?
Squirrel-cage rotor.
2000 watts
Draw less current.
600 volts.

36. Three-phase AC underground cables must be provided with overcurrent protection using a...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Circuit Breaker.
Draw less current.
2000 watts

37. 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...
They must be installed at least 7 feet above the ground.
Tied together
15 feet off the ground.
Second-degree burn.

38. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
The motor rotation is reversed.
60 Hertz
Four times less than that of the secondary.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

39. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Squirrel-cage induction motor.
Grounded phase and ground fault devices were not operating.
An electromagnet.
480 volts.

40. Current that changes periodically in direction is...
Alternating current.
H terminals.
3 -979 Volts.
Four times less than that of the secondary.

41. 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
Draw less current.
Isolation transformer.
Squirrel-cage induction motor.

42. 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.
It provides good speed control.
15 feet off the ground.
800 volts.

43. 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.
15 feet off the ground.
Second-degree burn.
Full-load - three-phase voltage.
5:1

44. 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?
800 volts.
Nearly constant.
Stator windings.
15 feet off the ground.

45. Not true about AC power?
They should be made by the same manufacturer.
It provides good speed control.
Two speeds
100 volts.

46. All transformers step voltage up or down by...
Draw less current.
60 Hertz
Inductance.
The current will read zero.

47. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
The capacitors should be discharged.
The chest should rise or inflate.
Disconnect the frame-grounding conductor.
At least two phases

48. Define alternating current...
Larger than that found in the primary winding.
60 Hertz
Stator windings.
Current changing constantly in magnitude and periodically in direction.

49. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Draw less current.
Isolation transformer.
The motor rotation is reversed.

50. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Reverse its rotation.
25 feet.
Current changing constantly in magnitude and periodically in direction.
Larger than that found in the primary winding.