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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. Current that changes periodically in direction is...
Carotid pulse - which is located in the neck next to the Adam's apple.
At the source transformer.
Alternating current.
Two speeds

2. To protect against over-current in a three-phase circuit over-current protection must be provided for...
60 Hertz
At least two phases
Inductance.
Draw less current.

3. If any two-phase wires are reversed on a three-phase motor - the motor will...
Full-load - three-phase voltage.
Reverse its rotation.
Reverse any two-phase leads.
Inductance.

4. High voltage is used to transmit power over long distances...
100 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
Electro-magnetism for their operation.
Kilovolt ampere (KVA).

5. A burn causing a blister is classified as a...
15 feet off the ground.
Second-degree burn.
Clamp-on ammeter.
60 Hertz

6. The size of a transformer is measured in...
Clamp-on ammeter.
Kilovolt ampere (KVA).
1 amp.
Transformer

7. The primary function of a power transformer is to provide...
Shunted and taped
15 feet off the ground.
Full-load - three-phase voltage.
Isolation transformer.

8. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Squirrel-cage induction motor.
A step-up transformer.
60 Hertz
An electrical shock hazard may exist.

9. All transformers step voltage up or down by...
The sum of the two capacitors.
Inductance.
Continuous.
Cut around clothing that has adhered to the burned area.

10. Not an acceptable method for the installations of surface transformers?
Tied together
Cut around clothing that has adhered to the burned area.
They should be made by the same manufacturer.
They must be installed at least 7 feet above the ground.

11. Which of the following does a squirrel cage induction motor have?
Disconnect the frame-grounding conductor.
Stator windings.
Alternating current.
1 amp.

12. The speed of an alternating current - squirrel-cage induction motor is...
75 turns.
Nearly constant.
277 volts.
Cut around clothing that has adhered to the burned area.

13. 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?
Derive a neutral for grounding purposes.
Kilovolt ampere (KVA).
600 volts.
25 feet.

14. Not true about AC power?
Squirrel-cage rotor.
It provides good speed control.
277 volts.
Potential transformer.

15. How should clothing be removed from a burn?
Draw less current.
Cut around clothing that has adhered to the burned area.
5:1.
Because less current flowing at high voltage causes less line loss per kilowatt.

16. Compared to the secondary of a loaded - step-down transformer - the primary has...
25 feet.
Potential transformer.
No.6 AWG.
Lower current and higher voltage.

17. 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...
Inductance.
Transformer
An electrical shock hazard may exist.
Tied together

18. 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 volts.
7 -630 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Two speeds

19. When not connected to a load - the secondary leads of a current transformer should be...
Stator windings.
600 volts.
Shunted and taped
Short-circuited after power has been removed.

20. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
H terminals.
25 feet.
Short-circuited after power has been removed.
7 -630 volts.

21. Where should grounding resistors be located?
Disconnect the frame-grounding conductor.
Draw less current.
At the source transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.

22. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Shunted and taped
Circuit Breaker.
Disconnect the frame-grounding conductor.
100 volts.

23. 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...
The current will read zero.
Draw less current.
75 turns.
Tied together

24. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
15 feet off the ground.
Alternating current.
1 amp.
An electrical shock hazard may exist.

25. What is the first step to be followed in aiding a victim of electrical shock?
3 -979 Volts.
Check to make sure that the victim is not still in contact with the electricity.
Lower current and higher voltage.
Potential transformer.

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

27. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
480 volts.
600 volts.
Reverse its rotation.

28. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Nearly constant.
A device used to store electrical energy.
Allow for metering voltage and Current.

29. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Hyperventilation.
Four times less than that of the secondary.
100 volts.

30. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Lower current and higher voltage
Squirrel-cage induction motor.
The capacitors should be discharged.
H terminals.

31. AC voltage is raised or lowered by means of...
An electromagnet.
Allow for metering voltage and Current.
Transformers.
12 to 15 times a minute.

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.
5:1.
Clamp-on ammeter.
Allow for metering voltage and Current.
They must be installed at least 7 feet above the ground.

33. The primary leads of a single-phase transformer should be connected to the...
H terminals.
The current will read zero.
The chest should rise or inflate.
2000 watts

34. A wound-rotor induction motor has all the following EXCEPT...
Lower current and higher voltage.
An electrical shock hazard may exist.
Squirrel-cage rotor.
Tied together

35. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The current will read zero.
Draw less current.

36. Define alternating current...
150 turns.
1 amp.
H terminals.
Current changing constantly in magnitude and periodically in direction.

37. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Zero amps.
The chest should rise or inflate.
Two speeds
2000 watts

38. 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.
Check to make sure that the victim is not still in contact with the electricity.
Reverse its rotation.
Four times less than that of the secondary.

39. Not a symptom of electrical shock?.
Second-degree burn.
An electrical shock hazard may exist.
Hyperventilation.
Zero amps.

40. What should the duty rating of a grounding resistor be?
75 turns.
Alternating current.
X.
Continuous.

41. The transformer used only to measure voltage is a...
Lower current and higher voltage
Potential transformer.
Derive a neutral for grounding purposes.
Tied together

42. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
An electromagnet.
Capacitance.
25 feet.
800 volts.

43. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
150 turns.
Alternating current.
Lower current and higher voltage.

44. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
5:1
The capacitors should be discharged.
No.6 AWG.
Derive a neutral for grounding purposes.

45. The main function of CT's and PT's on a main substation is to...
It provides good speed control.
75 turns.
Allow for metering voltage and Current.
100 turns.

46. 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?
Squirrel-cage rotor.
A device used to store electrical energy.
200 volts AC.
They should be made by the same manufacturer.

47. What is the danger when working around capacitors?
Short-circuited after power has been removed.
480 volts.
Squirrel-cage induction motor.
An electrical shock hazard may exist.

48. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Full-load - three-phase voltage.
Inductance.
15 feet off the ground.
Squirrel-cage rotor.

49. 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?
480 volts.
800 volts.
1 amp.
The capacitors should be discharged.

50. Compared to the secondary of a loaded - step-down transformer - the primary has...
100 volts.
Second-degree burn.
Lower current and higher voltage
600 volts.