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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. Which of the following does a squirrel cage induction motor have?
Hyperventilation.
A grounding resistor.
Stator windings.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

2. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
A grounding resistor.
A.C.
Four times less than that of the secondary.

3. A burn causing a blister is classified as a...
Current changing constantly in magnitude and periodically in direction.
100 turns.
Second-degree burn.
Zero amps.

4. A solenoid coil is...
Circuit Breaker.
Squirrel-cage induction motor.
An electromagnet.
Inductance.

5. When not connected to a load - the secondary leads of a current transformer should be...
A.C.
Shunted and taped
H terminals.
Two speeds

6. The property of an electric circuit that opposes any change in current is called...
75 turns.
Inductance.
5:1.
A step-up transformer.

7. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
12 to 15 times a minute.
Grounded phase and ground fault devices were not operating.
Shunted and taped
Short-circuited after power has been removed.

8. The main function of CT's and PT's on a main substation is to...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Kilovolt ampere (KVA).
Allow for metering voltage and Current.
Inductance.

9. If any two-phase wires are reversed on a three-phase motor - the motor will...
Capacitance.
At the source transformer.
3 -979 Volts.
Reverse its rotation.

10. How should clothing be removed from a burn?
Transformer
Cut around clothing that has adhered to the burned area.
Stator windings.
The motor rotation is reversed.

11. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Alternating current.
The current will read zero.
Derive a neutral for grounding purposes.
Lower current and higher voltage

12. The size of a transformer is measured in...
Kilovolt ampere (KVA).
Second-degree burn.
H terminals.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

13. 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?
A device used to store electrical energy.
An electromagnet.
Squirrel-cage rotor.
75 turns.

14. What steps up or steps down AC voltage?
Transformer
Check to make sure that the victim is not still in contact with the electricity.
Cut around clothing that has adhered to the burned area.
Because less current flowing at high voltage causes less line loss per kilowatt.

15. 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...
15 feet off the ground.
Draw less current.
The sum of the two capacitors.
2000 watts

16. Not an acceptable method for the installations of surface transformers?
Draw less current.
They must be installed at least 7 feet above the ground.
Four times less than that of the secondary.
12 to 15 times a minute.

17. 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...
Draw less current.
Clamp-on ammeter.
They must be installed at least 7 feet above the ground.
12 to 15 times a minute.

18. High voltage is used to transmit power over long distances...
Allow for metering voltage and Current.
Continuous.
Because less current flowing at high voltage causes less line loss per kilowatt.
Transformers.

19. 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.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Larger than that found in the primary winding.
5:1
1 amp.

20. 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?
A device used to store electrical energy.
100 turns.
Lower current and higher voltage.
Allow for metering voltage and Current.

21. All transformers step voltage up or down by...
No.6 AWG.
Tied together
Inductance.
Transformer

22. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
The sum of the two capacitors.
1 amp.
25 feet.
Lower current and higher voltage

23. How do you change the direction of a 3-phase AC motor?
Continuous.
Provides single-phase power to smaller loads such as lights - heaters - etc.
They should be made by the same manufacturer.
Reverse any two-phase leads.

24. 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.
Hyperventilation.
Reverse its rotation.
Current that changes constantly in magnitude and periodically in direction.

25. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Because less current flowing at high voltage causes less line loss per kilowatt.
Two speeds
At least two phases
Capacitance.

26. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
12 to 15 times a minute.
Isolation transformer.
Zero amps.

27. A wound-rotor induction motor has all the following EXCEPT...
It provides good speed control.
Reverse any two-phase leads.
Check to make sure that the victim is not still in contact with the electricity.
Squirrel-cage rotor.

28. The standard frequency of alternating current used at a mine is...
60 Hertz
An electrical shock hazard may exist.
Disconnect the frame-grounding conductor.
Draw less current.

29. The standard frequency of power supplied by the power company is...
Two speeds
The capacitors should be discharged.
H terminals.
60 cycles per second (60 Hertz).

30. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Two speeds
Current that changes constantly in magnitude and periodically in direction.
The current will read zero.

31. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A device used to store electrical energy.
Lower current and higher voltage.
A grounding resistor.
An electromagnet.

32. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
200 volts AC.
Shunted and taped
25 feet.
480 volts.

33. 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?
Current that changes constantly in magnitude and periodically in direction.
The capacitors should be discharged.
Lower current and higher voltage
3 -979 Volts.

34. Compared to the secondary of a loaded - step-down transformer - the primary has...
Reverse any two-phase leads.
150 turns.
Lower current and higher voltage.
800 volts.

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?
600 volts.
At the source transformer.
Clamp-on ammeter.
The chest should rise or inflate.

36. The secondary windings on a 10:1 step-down transformer will have a wire size...
A grounding resistor.
Larger than that found in the primary winding.
Check to make sure that the victim is not still in contact with the electricity.
100 volts.

37. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
25 feet.
The capacitors should be discharged.
Provides single-phase power to smaller loads such as lights - heaters - etc.
12 to 15 times a minute.

38. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
480 volts.
The chest should rise or inflate.
60 Hertz
Reverse its rotation.

39. A transformer with a 1:1 ratio is usually a (an)...
Draw less current.
2000 watts
Draw less current.
Isolation transformer.

40. What is a capacitor?
A grounding resistor.
A device used to store electrical energy.
Potential transformer.
Disconnect the frame-grounding conductor.

41. Not a symptom of electrical shock?.
Hyperventilation.
100 turns.
200 volts AC.
Circuit Breaker.

42. What is the first step to be followed in aiding a victim of electrical shock?
Provides single-phase power to smaller loads such as lights - heaters - etc.
At least two phases
Check to make sure that the victim is not still in contact with the electricity.
200 volts AC.

43. The primary leads of a single-phase transformer should be connected to the...
H terminals.
The capacitors should be discharged.
They should be made by the same manufacturer.
15 feet off the ground.

44. Operating coils - motors - transformers - relays and solenoids depend upon...
5:1.
Current that changes constantly in magnitude and periodically in direction.
Electro-magnetism for their operation.
A device used to store electrical energy.

45. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Alternating current.
Grounded phase and ground fault devices were not operating.
At least two phases
100 volts.

46. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
75 turns.
The motor rotation is reversed.
3 -979 Volts.
7 -630 volts.

47. Where should grounding resistors be located?
Stator windings.
Reverse its rotation.
At the source transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.

48. 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...
Short-circuited after power has been removed.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Tied together
The chest should rise or inflate.

49. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
Larger than that found in the primary winding.
It provides good speed control.
75 turns.

50. The purpose of a zig-zag transformer is to...
The current will read zero.
Derive a neutral for grounding purposes.
100 volts.
Reverse its rotation.