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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 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?
Current that changes constantly in magnitude and periodically in direction.
600 volts.
Second-degree burn.
100 turns.

2. 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.
Stator windings.
Grounded phase and ground fault devices were not operating.
480 volts.

3. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Draw less current.
They should be made by the same manufacturer.
Reverse its rotation.
Continuous.

4. The purpose of a zig-zag transformer is to...
Inductance.
Derive a neutral for grounding purposes.
Two speeds
Carotid pulse - which is located in the neck next to the Adam's apple.

5. A control power transformer...
Short-circuited after power has been removed.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Larger than that found in the primary winding.
Electro-magnetism for their operation.

6. The size of a transformer is measured in...
A grounding resistor.
75 turns.
Kilovolt ampere (KVA).
Two speeds

7. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
Current that changes constantly in magnitude and periodically in direction.
No.6 AWG.
They must be installed at least 7 feet above the ground.

8. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
Check to make sure that the victim is not still in contact with the electricity.
Grounded phase and ground fault devices were not operating.
Full-load - three-phase voltage.

9. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Because less current flowing at high voltage causes less line loss per kilowatt.
Shunted and taped
480 volts.
Hyperventilation.

10. 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...
Clamp-on ammeter.
7 -630 volts.
An electrical shock hazard may exist.
Tied together

11. Alternating current may be defined as...
Inductance.
5:1.
Shunted and taped
Current that changes constantly in magnitude and periodically in direction.

12. When not connected to a load - the secondary leads of a current transformer should be...
The chest should rise or inflate.
Shunted and taped
Isolation transformer.
Reverse any two-phase leads.

13. Three-phase AC underground cables must be provided with overcurrent protection using a...
2000 watts
Circuit Breaker.
They must be installed at least 7 feet above the ground.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

14. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Stator windings.
Grounded phase and ground fault devices were not operating.
Zero amps.
Disconnect the frame-grounding conductor.

15. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
100 turns.
Second-degree burn.
Zero amps.
Two speeds

16. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
Isolation transformer.
Squirrel-cage rotor.
Alternating current.

17. The property of an electrical circuit that opposes any change in voltage is called...
15 feet off the ground.
No.6 AWG.
Draw less current.
Capacitance.

18. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Circuit Breaker.
Zero amps.
The capacitors should be discharged.
The motor rotation is reversed.

19. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
An electromagnet.
The current will read zero.
5:1
Grounded phase and ground fault devices were not operating.

20. 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.
Nearly constant.
75 turns.
Isolation transformer.

21. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Check to make sure that the victim is not still in contact with the electricity.
Allow for metering voltage and Current.
15 feet off the ground.
Circuit Breaker.

22. Compared to the secondary of a loaded - step-down transformer - the primary has...
Electro-magnetism for their operation.
Lower current and higher voltage
Allow for metering voltage and Current.
At the source transformer.

23. 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.
Full-load - three-phase voltage.
3 -979 Volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.

24. A burn causing a blister is classified as a...
Second-degree burn.
Hyperventilation.
277 volts.
Lower current and higher voltage

25. 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?
At least two phases
200 volts AC.
The sum of the two capacitors.
Isolation transformer.

26. What type motor is a wound-rotor induction motor?
A.C.
Lower current and higher voltage
Continuous.
The current will read zero.

27. If any two-phase wires are reversed on a three-phase motor - the motor will...
15 feet off the ground.
The current will read zero.
Reverse its rotation.
Potential transformer.

28. Which of the following does a squirrel cage induction motor have?
Four times less than that of the secondary.
It provides good speed control.
Stator windings.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

29. 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.
A grounding resistor.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
A device used to store electrical energy.

30. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Reverse any two-phase leads.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The chest should rise or inflate.
A grounding resistor.

31. Compared to the secondary of a loaded - step-down transformer - the primary has...
At the source transformer.
Lower current and higher voltage.
100 turns.
Second-degree burn.

32. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
3 -979 Volts.
A.C.
480 volts.

33. All transformers step voltage up or down by...
Kilovolt ampere (KVA).
100 turns.
Inductance.
The capacitors should be discharged.

34. What is a capacitor?
A device used to store electrical energy.
Lower current and higher voltage.
150 turns.
Circuit Breaker.

35. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Because less current flowing at high voltage causes less line loss per kilowatt.
277 volts.
Allow for metering voltage and Current.
An electrical shock hazard may exist.

36. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
15 feet off the ground.
Current changing constantly in magnitude and periodically in direction.
60 Hertz

37. What is the danger when working around capacitors?
A.C.
An electrical shock hazard may exist.
Reverse its rotation.
Tied together

38. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A.C.
A grounding resistor.
X.
A step-up transformer.

39. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Kilovolt ampere (KVA).
X.
3 -979 Volts.
Transformers.

40. To protect against over-current in a three-phase circuit over-current protection must be provided for...
They must be installed at least 7 feet above the ground.
At least two phases
A grounding resistor.
Reverse any two-phase leads.

41. Not true about AC power?
Squirrel-cage induction motor.
12 to 15 times a minute.
It provides good speed control.
Continuous.

42. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Short-circuited after power has been removed.
Clamp-on ammeter.
Tied together
60 cycles per second (60 Hertz).

43. 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...
5:1.
100 volts.
Allow for metering voltage and Current.
Check to make sure that the victim is not still in contact with the electricity.

44. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Short-circuited after power has been removed.
Carotid pulse - which is located in the neck next to the Adam's apple.
12 to 15 times a minute.
No.6 AWG.

45. A solenoid coil is...
Kilovolt ampere (KVA).
An electromagnet.
15 feet off the ground.
Inductance.

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

47. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Shunted and taped
Four times less than that of the secondary.
Because less current flowing at high voltage causes less line loss per kilowatt.
Lower current and higher voltage.

48. 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.
Tied together
The chest should rise or inflate.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

49. What steps up or steps down AC voltage?
They should be made by the same manufacturer.
75 turns.
Two speeds
Transformer

50. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
A device used to store electrical energy.
Continuous.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.