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AC Theory

Instructions:

Answer 50 questions in 15 minutes.
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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 with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Draw less current.
Because less current flowing at high voltage causes less line loss per kilowatt.
A step-up transformer.
X.

2. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
A.C.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
They should be made by the same manufacturer.
277 volts.

3. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Because less current flowing at high voltage causes less line loss per kilowatt.
Four times less than that of the secondary.
Clamp-on ammeter.
Continuous.

4. Compared to the secondary of a loaded - step-down transformer - the primary has...
60 Hertz
480 volts.
Lower current and higher voltage
A.C.

5. Compared to the secondary of a loaded - step-down transformer - the primary has...
Kilovolt ampere (KVA).
Lower current and higher voltage.
Inductance.
Short-circuited after power has been removed.

6. A burn causing a blister is classified as a...
Current changing constantly in magnitude and periodically in direction.
Inductance.
A step-up transformer.
Second-degree burn.

7. Current that changes periodically in direction is...
Potential transformer.
Check to make sure that the victim is not still in contact with the electricity.
Alternating current.
Current changing constantly in magnitude and periodically in direction.

8. The secondary windings on a 10:1 step-down transformer will have a wire size...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Larger than that found in the primary winding.
X.
Lower current and higher voltage.

9. Not a symptom of electrical shock?.
15 feet off the ground.
3 -979 Volts.
Inductance.
Hyperventilation.

10. A wound-rotor induction motor has all the following EXCEPT...
Circuit Breaker.
Carotid pulse - which is located in the neck next to the Adam's apple.
The sum of the two capacitors.
Squirrel-cage rotor.

11. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
75 turns.
Squirrel-cage induction motor.
Two speeds
The current will read zero.

12. Current transformers - or CT's - are used to...
7 -630 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
100 turns.
5:1.

13. AC voltage is raised or lowered by means of...
Zero amps.
H terminals.
The motor rotation is reversed.
Transformers.

14. What should the duty rating of a grounding resistor be?
Continuous.
They should be made by the same manufacturer.
The chest should rise or inflate.
Inductance.

15. A transformer with a 1:1 ratio is usually a (an)...
Lower current and higher voltage.
Reverse any two-phase leads.
Isolation transformer.
Circuit Breaker.

16. 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.
Because less current flowing at high voltage causes less line loss per kilowatt.
Lower current and higher voltage.
Electro-magnetism for their operation.

17. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
480 volts.
Transformer
The capacitors should be discharged.
Provides single-phase power to smaller loads such as lights - heaters - etc.

18. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
At least two phases
Larger than that found in the primary winding.
Provides single-phase power to smaller loads such as lights - heaters - etc.

19. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Isolation transformer.
A grounding resistor.
200 volts AC.
Lower current and higher voltage

20. What type of 3-phase AC motor is used most often around a mine?
Cut around clothing that has adhered to the burned area.
Squirrel-cage induction motor.
Nearly constant.
They should be made by the same manufacturer.

21. What is the danger when working around capacitors?
Current changing constantly in magnitude and periodically in direction.
Continuous.
Reverse any two-phase leads.
An electrical shock hazard may exist.

22. The primary leads of a single-phase transformer should be connected to the...
H terminals.
Isolation transformer.
600 volts.
Shunted and taped

23. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
Stator windings.
600 volts.
Hyperventilation.

24. The size of a transformer is measured in...
Kilovolt ampere (KVA).
12 to 15 times a minute.
Current changing constantly in magnitude and periodically in direction.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

25. 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?
Full-load - three-phase voltage.
7 -630 volts.
3 -979 Volts.
150 turns.

26. When not connected to a load - the secondary leads of a current transformer should be...
60 Hertz
75 turns.
Shunted and taped
Because less current flowing at high voltage causes less line loss per kilowatt.

27. The standard frequency of power supplied by the power company is...
A step-up transformer.
Full-load - three-phase voltage.
Capacitance.
60 cycles per second (60 Hertz).

28. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
An electromagnet.
Grounded phase and ground fault devices were not operating.
At the source transformer.
They must be installed at least 7 feet above the ground.

29. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
It provides good speed control.
Draw less current.
Allow for metering voltage and Current.

30. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
15 feet off the ground.
150 turns.
480 volts.
They should be made by the same manufacturer.

31. 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...
100 turns.
2000 watts
Draw less current.
Four times less than that of the secondary.

32. The transformer used only to measure voltage is a...
25 feet.
Potential transformer.
X.
Draw less current.

33. How should clothing be removed from a burn?
Isolation transformer.
Cut around clothing that has adhered to the burned area.
Current changing constantly in magnitude and periodically in direction.
Kilovolt ampere (KVA).

34. At what rate should mouth-to-mouth resuscitation be applied?
The capacitors should be discharged.
Shunted and taped
Zero amps.
12 to 15 times a minute.

35. 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
Cut around clothing that has adhered to the burned area.
Hyperventilation.
A.C.

36. A solenoid coil is...
Inductance.
An electromagnet.
They should be made by the same manufacturer.
Transformers.

37. Which of the following does a squirrel cage induction motor have?
150 turns.
277 volts.
Stator windings.
Kilovolt ampere (KVA).

38. All transformers step voltage up or down by...
Inductance.
Electro-magnetism for their operation.
Capacitance.
Because less current flowing at high voltage causes less line loss per kilowatt.

39. What type motor is a wound-rotor induction motor?
A.C.
3 -979 Volts.
60 cycles per second (60 Hertz).
An electromagnet.

40. Where should grounding resistors be located?
100 turns.
X.
At least two phases
At the source transformer.

41. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
A.C.
Second-degree burn.
Reverse any two-phase leads.
Short-circuited after power has been removed.

42. 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...
Transformer
H terminals.
100 volts.
A step-up transformer.

43. The standard frequency of alternating current used at a mine is...
Cut around clothing that has adhered to the burned area.
7 -630 volts.
The motor rotation is reversed.
60 Hertz

44. 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.
5:1
12 to 15 times a minute.
Alternating current.

45. Not an acceptable method for the installations of surface transformers?
Disconnect the frame-grounding conductor.
7 -630 volts.
An electromagnet.
They must be installed at least 7 feet above the ground.

46. The property of an electrical circuit that opposes any change in voltage is called...
An electrical shock hazard may exist.
Potential transformer.
Disconnect the frame-grounding conductor.
Capacitance.

47. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
Transformers.
A step-up transformer.
Carotid pulse - which is located in the neck next to the Adam's apple.

48. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Capacitance.
Draw less current.
Tied together
Disconnect the frame-grounding conductor.

49. What steps up or steps down AC voltage?
Transformer
Second-degree burn.
Clamp-on ammeter.
277 volts.

50. Three-phase AC underground cables must be provided with overcurrent protection using a...
75 turns.
60 cycles per second (60 Hertz).
Nearly constant.
Circuit Breaker.

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AC Theory

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