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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 main function of CT's and PT's on a main substation is to...
Nearly constant.
200 volts AC.
Allow for metering voltage and Current.
Transformer

2. The standard frequency of power supplied by the power company is...
277 volts.
60 cycles per second (60 Hertz).
Carotid pulse - which is located in the neck next to the Adam's apple.
100 volts.

3. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
7 -630 volts.
Nearly constant.
1 amp.

4. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
Inductance.
277 volts.
Reverse its rotation.

5. 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...
At the source transformer.
X.
Squirrel-cage induction motor.
Draw less current.

6. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Check to make sure that the victim is not still in contact with the electricity.
Short-circuited after power has been removed.

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

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8. Which of the following does a squirrel cage induction motor have?
25 feet.
Stator windings.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Grounded phase and ground fault devices were not operating.

9. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
480 volts.
7 -630 volts.
150 turns.
1 amp.

10. The transformer used only to measure voltage is a...
Allow for metering voltage and Current.
Because less current flowing at high voltage causes less line loss per kilowatt.
A grounding resistor.
Potential transformer.

11. Alternating current may be defined as...
Inductance.
Current that changes constantly in magnitude and periodically in direction.
800 volts.
Check to make sure that the victim is not still in contact with the electricity.

12. Operating coils - motors - transformers - relays and solenoids depend upon...
X.
Electro-magnetism for their operation.
The motor rotation is reversed.
A device used to store electrical energy.

13. What type of 3-phase AC motor is used most often around a mine?
A grounding resistor.
Circuit Breaker.
The motor rotation is reversed.
Squirrel-cage induction motor.

14. Define alternating current...
Cut around clothing that has adhered to the burned area.
Larger than that found in the primary winding.
They must be installed at least 7 feet above the ground.
Current changing constantly in magnitude and periodically in direction.

15. Not true about AC power?
A grounding resistor.
Second-degree burn.
Lower current and higher voltage.
It provides good speed control.

16. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
At the source transformer.
200 volts AC.
Second-degree burn.

17. 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?
The chest should rise or inflate.
An electrical shock hazard may exist.
75 turns.
800 volts.

18. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Inductance.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
2000 watts
25 feet.

19. The property of an electric circuit that opposes any change in current is called...
Four times less than that of the secondary.
7 -630 volts.
Inductance.
Draw less current.

20. The purpose of a zig-zag transformer is to...
Draw less current.
5:1
Full-load - three-phase voltage.
Derive a neutral for grounding purposes.

21. Current transformers - or CT's - are used to...
They should be made by the same manufacturer.
Clamp-on ammeter.
X.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

22. Compared to the secondary of a loaded - step-down transformer - the primary has...
60 Hertz
Lower current and higher voltage
A step-up transformer.
100 volts.

23. The primary function of a power transformer is to provide...
60 cycles per second (60 Hertz).
Full-load - three-phase voltage.
Disconnect the frame-grounding conductor.
75 turns.

24. 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...
X.
Tied together
Lower current and higher voltage
They should be made by the same manufacturer.

25. The primary leads of a single-phase transformer should be connected to the...
Lower current and higher voltage.
Larger than that found in the primary winding.
Because less current flowing at high voltage causes less line loss per kilowatt.
H terminals.

26. 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...
1 amp.
150 turns.
Draw less current.
15 feet off the ground.

27. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
15 feet off the ground.
Short-circuited after power has been removed.
The capacitors should be discharged.
A.C.

28. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Allow for metering voltage and Current.
Second-degree burn.
Two speeds
2000 watts

29. At what rate should mouth-to-mouth resuscitation be applied?
Provides single-phase power to smaller loads such as lights - heaters - etc.
12 to 15 times a minute.
Hyperventilation.
5:1.

30. High voltage is used to transmit power over long distances...
800 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
25 feet.
Larger than that found in the primary winding.

31. Current in an AC circuit may be measured by...
Lower current and higher voltage.
Because less current flowing at high voltage causes less line loss per kilowatt.
480 volts.
Clamp-on ammeter.

32. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
Alternating current.
Short-circuited after power has been removed.
A device used to store electrical energy.

33. 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?
Tied together
800 volts.
Short-circuited after power has been removed.
Reverse its rotation.

34. The standard frequency of alternating current used at a mine is...
60 Hertz
They should be made by the same manufacturer.
The motor rotation is reversed.
75 turns.

35. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
Allow for metering voltage and Current.
An electrical shock hazard may exist.
X.

36. 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.
Potential transformer.
Disconnect the frame-grounding conductor.
15 feet off the ground.

37. What is a capacitor?
Two speeds
A device used to store electrical energy.
Reverse any two-phase leads.
Alternating current.

38. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
200 volts AC.
An electrical shock hazard may exist.
800 volts.

39. 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
1 amp.
Potential transformer.
H terminals.

40. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Inductance.
Because less current flowing at high voltage causes less line loss per kilowatt.
277 volts.
Capacitance.

41. The combined capacitance of two capacitors in parallel is...
60 cycles per second (60 Hertz).
Clamp-on ammeter.
Cut around clothing that has adhered to the burned area.
The sum of the two capacitors.

42. How should clothing be removed from a burn?
Transformer
480 volts.
Cut around clothing that has adhered to the burned area.
Clamp-on ammeter.

43. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
The motor rotation is reversed.
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.
Short-circuited after power has been removed.

44. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Shunted and taped
Four times less than that of the secondary.
A step-up transformer.

45. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Shunted and taped
Disconnect the frame-grounding conductor.
X.
No.6 AWG.

46. What is the danger when working around capacitors?
An electrical shock hazard may exist.
No.6 AWG.
The motor rotation is reversed.
Full-load - three-phase voltage.

47. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Allow for metering voltage and Current.
The capacitors should be discharged.
The chest should rise or inflate.
Second-degree burn.

48. What should the duty rating of a grounding resistor be?
100 turns.
Continuous.
Transformers.
No.6 AWG.

49. 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.
100 volts.
Alternating current.
They should be made by the same manufacturer.

50. All transformers step voltage up or down by...
Shunted and taped
The capacitors should be discharged.
Electro-magnetism for their operation.
Inductance.