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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. What is a capacitor?
100 volts.
A step-up transformer.
60 Hertz
A device used to store electrical energy.

2. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
H terminals.
Grounded phase and ground fault devices were not operating.
800 volts.
600 volts.

3. Alternating current may be defined as...
The sum of the two capacitors.
Draw less current.
Current that changes constantly in magnitude and periodically in direction.
Larger than that found in the primary winding.

4. A control power transformer...
Draw less current.
Inductance.
Transformer
Provides single-phase power to smaller loads such as lights - heaters - etc.

5. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Disconnect the frame-grounding conductor.
Nearly constant.
150 turns.

6. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Clamp-on ammeter.
Lower current and higher voltage
480 volts.
2000 watts

7. How should clothing be removed from a burn?
Check to make sure that the victim is not still in contact with the electricity.
Transformer
Cut around clothing that has adhered to the burned area.
Isolation transformer.

8. The property of an electric circuit that opposes any change in current is called...
2000 watts
Transformers.
Inductance.
Kilovolt ampere (KVA).

9. 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
2000 watts
150 turns.
Allow for metering voltage and Current.

10. What steps up or steps down AC voltage?
They should be made by the same manufacturer.
Continuous.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Transformer

11. At what rate should mouth-to-mouth resuscitation be applied?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Two speeds
12 to 15 times a minute.
The chest should rise or inflate.

12. The standard frequency of power supplied by the power company is...
Lower current and higher voltage.
60 cycles per second (60 Hertz).
The motor rotation is reversed.
They should be made by the same manufacturer.

13. What type of 3-phase AC motor is used most often around a mine?
25 feet.
Squirrel-cage induction motor.
It provides good speed control.
Isolation transformer.

14. 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.
200 volts AC.
An electrical shock hazard may exist.
5:1
60 cycles per second (60 Hertz).

15. The purpose of a zig-zag transformer is to...
Draw less current.
They must be installed at least 7 feet above the ground.
Transformers.
Derive a neutral for grounding purposes.

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

17. 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?
Reverse its rotation.
277 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
200 volts AC.

18. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
At the source transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
A.C.
277 volts.

19. A burn causing a blister is classified as a...
5:1
Second-degree burn.
Short-circuited after power has been removed.
60 cycles per second (60 Hertz).

20. Three-phase AC underground cables must be provided with overcurrent protection using a...
Potential transformer.
Lower current and higher voltage
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Circuit Breaker.

21. Current in an AC circuit may be measured by...
Nearly constant.
An electrical shock hazard may exist.
Clamp-on ammeter.
100 volts.

22. The combined capacitance of two capacitors in parallel is...
An electrical shock hazard may exist.
The sum of the two capacitors.
The chest should rise or inflate.
60 Hertz

23. All transformers step voltage up or down by...
Circuit Breaker.
Inductance.
Hyperventilation.
Allow for metering voltage and Current.

24. The primary leads of a single-phase transformer should be connected to the...
H terminals.
No.6 AWG.
3 -979 Volts.
12 to 15 times a minute.

25. What is the first step to be followed in aiding a victim of electrical shock?
Inductance.
Check to make sure that the victim is not still in contact with the electricity.
60 Hertz
Lower current and higher voltage.

26. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Inductance.
Tied together
Cut around clothing that has adhered to the burned area.
Short-circuited after power has been removed.

27. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Squirrel-cage induction motor.
Zero amps.
A.C.
480 volts.

28. 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.
An electromagnet.
It provides good speed control.
Isolation transformer.

29. Define alternating current...
Short-circuited after power has been removed.
An electromagnet.
Current changing constantly in magnitude and periodically in direction.
277 volts.

30. Where should grounding resistors be located?
At the source transformer.
The sum of the two capacitors.
277 volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.

31. 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...
Tied together
Two speeds
Electro-magnetism for their operation.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

32. The secondary windings on a 10:1 step-down transformer will have a wire size...
They should be made by the same manufacturer.
Reverse its rotation.
Larger than that found in the primary winding.
A step-up transformer.

33. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
60 cycles per second (60 Hertz).
7 -630 volts.
Transformer
Circuit Breaker.

34. Current transformers - or CT's - are used to...
Reverse any two-phase leads.
15 feet off the ground.
3 -979 Volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

35. The speed of an alternating current - squirrel-cage induction motor is...
They should be made by the same manufacturer.
Nearly constant.
Transformers.
60 cycles per second (60 Hertz).

36. A transformer with 3000 turns in the primary winding has a primary voltage of 4 -800 volts and a secondary voltage of 240 volts. How many turns are in the secondary winding?
Carotid pulse - which is located in the neck next to the Adam's apple.
150 turns.
Lower current and higher voltage.
Stator windings.

37. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Grounded phase and ground fault devices were not operating.
Disconnect the frame-grounding conductor.
75 turns.
A.C.

38. The transformer used only to measure voltage is a...
Current changing constantly in magnitude and periodically in direction.
Potential transformer.
150 turns.
Disconnect the frame-grounding conductor.

39. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
277 volts.
Transformers.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Draw less current.

40. 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.
Transformers.
100 volts.
At the source transformer.

41. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Carotid pulse - which is located in the neck next to the Adam's apple.
Allow for metering voltage and Current.
Draw less current.

42. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
12 to 15 times a minute.
1 amp.
150 turns.
An electromagnet.

43. A transformer with a 1:1 ratio is usually a (an)...
Alternating current.
Cut around clothing that has adhered to the burned area.
Isolation transformer.
200 volts AC.

44. AC voltage is raised or lowered by means of...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Transformers.
600 volts.
Shunted and taped

45. 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.
A device used to store electrical energy.
Squirrel-cage rotor.
600 volts.

46. 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...
Zero amps.
An electrical shock hazard may exist.
Draw less current.
3 -979 Volts.

47. The size of a transformer is measured in...
Stator windings.
1 amp.
Electro-magnetism for their operation.
Kilovolt ampere (KVA).

48. Current that changes periodically in direction is...
Derive a neutral for grounding purposes.
Alternating current.
5:1
Because less current flowing at high voltage causes less line loss per kilowatt.

49. What should the duty rating of a grounding resistor be?
3 -979 Volts.
Continuous.
Derive a neutral for grounding purposes.
An electromagnet.

50. A solenoid coil is...
An electromagnet.
Capacitance.
Because less current flowing at high voltage causes less line loss per kilowatt.
Current changing constantly in magnitude and periodically in direction.