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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. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
Stator windings.
100 volts.
Clamp-on ammeter.

2. 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...
Squirrel-cage rotor.
Tied together
An electromagnet.
60 cycles per second (60 Hertz).

3. Operating coils - motors - transformers - relays and solenoids depend upon...
It provides good speed control.
Electro-magnetism for their operation.
Isolation transformer.
Grounded phase and ground fault devices were not operating.

4. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
100 turns.
Continuous.
The capacitors should be discharged.

5. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Four times less than that of the secondary.
200 volts AC.
No.6 AWG.
Grounded phase and ground fault devices were not operating.

6. 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
480 volts.
At least two phases
An electrical shock hazard may exist.

7. Not an acceptable method for the installations of surface transformers?
Because less current flowing at high voltage causes less line loss per kilowatt.
Shunted and taped
The capacitors should be discharged.
They must be installed at least 7 feet above the ground.

8. The secondary windings on a 10:1 step-down transformer will have a wire size...
A device used to store electrical energy.
Allow for metering voltage and Current.
Capacitance.
Larger than that found in the primary winding.

9. 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
480 volts.
Derive a neutral for grounding purposes.
Nearly constant.

10. Which of the following does a squirrel cage induction motor have?
Stator windings.
Inductance.
2000 watts
An electrical shock hazard may exist.

11. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
5:1
Zero amps.
100 volts.
Current that changes constantly in magnitude and periodically in direction.

12. 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...
Draw less current.
200 volts AC.
Cut around clothing that has adhered to the burned area.
Derive a neutral for grounding purposes.

13. The standard frequency of power supplied by the power company is...
Carotid pulse - which is located in the neck next to the Adam's apple.
60 cycles per second (60 Hertz).
Transformers.
Grounded phase and ground fault devices were not operating.

14. What is the first step to be followed in aiding a victim of electrical shock?
X.
Two speeds
Allow for metering voltage and Current.
Check to make sure that the victim is not still in contact with the electricity.

15. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Four times less than that of the secondary.
Kilovolt ampere (KVA).
They should be made by the same manufacturer.
Inductance.

16. 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...
5:1
The capacitors should be discharged.
Draw less current.
60 Hertz

17. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
Current that changes constantly in magnitude and periodically in direction.
It provides good speed control.
Kilovolt ampere (KVA).

18. 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?
Lower current and higher voltage.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
100 volts.
75 turns.

19. The property of an electric circuit that opposes any change in current is called...
Allow for metering voltage and Current.
Inductance.
The motor rotation is reversed.
H terminals.

20. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
At least two phases
Alternating current.
Current that changes constantly in magnitude and periodically in direction.

21. The size of a transformer is measured in...
Kilovolt ampere (KVA).
H terminals.
X.
The chest should rise or inflate.

22. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Draw less current.
Reverse its rotation.
15 feet off the ground.
200 volts AC.

23. 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.
15 feet off the ground.
60 Hertz
Nearly constant.

24. Compared to the secondary of a loaded - step-down transformer - the primary has...
Check to make sure that the victim is not still in contact with the electricity.
Lower current and higher voltage
Nearly constant.
Allow for metering voltage and Current.

25. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
Lower current and higher voltage
Draw less current.
25 feet.

26. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Carotid pulse - which is located in the neck next to the Adam's apple.
277 volts.
The chest should rise or inflate.
Disconnect the frame-grounding conductor.

27. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Provides single-phase power to smaller loads such as lights - heaters - etc.
The current will read zero.
They must be installed at least 7 feet above the ground.
Disconnect the frame-grounding conductor.

28. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
An electromagnet.
H terminals.
5:1.
1 amp.

29. The speed of an alternating current - squirrel-cage induction motor is...
Inductance.
An electrical shock hazard may exist.
Allow for metering voltage and Current.
Nearly constant.

30. What should the duty rating of a grounding resistor be?
Continuous.
Zero amps.
Because less current flowing at high voltage causes less line loss per kilowatt.
Check to make sure that the victim is not still in contact with the electricity.

31. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Second-degree burn.
Kilovolt ampere (KVA).
Because less current flowing at high voltage causes less line loss per kilowatt.

32. Alternating current may be defined as...
Cut around clothing that has adhered to the burned area.
Current that changes constantly in magnitude and periodically in direction.
An electrical shock hazard may exist.
3 -979 Volts.

33. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Disconnect the frame-grounding conductor.
A.C.
200 volts AC.

34. A solenoid coil is...
Allow for metering voltage and Current.
Continuous.
Current that changes constantly in magnitude and periodically in direction.
An electromagnet.

35. 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...
Reverse its rotation.
Inductance.
100 volts.
It provides good speed control.

36. The combined capacitance of two capacitors in parallel is...
15 feet off the ground.
The sum of the two capacitors.
No.6 AWG.
75 turns.

37. 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?
Two speeds
Lower current and higher voltage.
Second-degree burn.
3 -979 Volts.

38. If any two-phase wires are reversed on a three-phase motor - the motor will...
An electrical shock hazard may exist.
The motor rotation is reversed.
Reverse its rotation.
Potential transformer.

39. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
An electromagnet.
Because less current flowing at high voltage causes less line loss per kilowatt.
A step-up transformer.
7 -630 volts.

40. A burn causing a blister is classified as a...
15 feet off the ground.
Second-degree burn.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
100 turns.

41. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
The current will read zero.
Squirrel-cage rotor.
Circuit Breaker.
Short-circuited after power has been removed.

42. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
At least two phases
480 volts.
Zero amps.
60 cycles per second (60 Hertz).

43. Not a symptom of electrical shock?.
Hyperventilation.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Check to make sure that the victim is not still in contact with the electricity.
100 volts.

44. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
60 Hertz
X.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
480 volts.

45. AC voltage is raised or lowered by means of...
They must be installed at least 7 feet above the ground.
75 turns.
Transformers.
Zero amps.

46. Not true about AC power?
Clamp-on ammeter.
Second-degree burn.
Full-load - three-phase voltage.
It provides good speed control.

47. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Grounded phase and ground fault devices were not operating.
Circuit Breaker.
At least two phases
H terminals.

48. The primary function of a power transformer is to provide...
Nearly constant.
Full-load - three-phase voltage.
Hyperventilation.
Lower current and higher voltage

49. What steps up or steps down AC voltage?
Short-circuited after power has been removed.
Four times less than that of the secondary.
Transformer
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

50. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Current that changes constantly in magnitude and periodically in direction.
Transformers.
At least two phases
Squirrel-cage induction motor.