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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. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Stator windings.
12 to 15 times a minute.
Four times less than that of the secondary.
X.

2. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
200 volts AC.
Continuous.
480 volts.
Four times less than that of the secondary.

3. The speed of an alternating current - squirrel-cage induction motor is...
Because less current flowing at high voltage causes less line loss per kilowatt.
Nearly constant.
800 volts.
Full-load - three-phase voltage.

4. Compared to the secondary of a loaded - step-down transformer - the primary has...
Transformer
Lower current and higher voltage.
Larger than that found in the primary winding.
Tied together

5. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Lower current and higher voltage.
Because less current flowing at high voltage causes less line loss per kilowatt.
No.6 AWG.
Provides single-phase power to smaller loads such as lights - heaters - etc.

6. A burn causing a blister is classified as a...
Electro-magnetism for their operation.
It provides good speed control.
Second-degree burn.
Grounded phase and ground fault devices were not operating.

7. What is a capacitor?
Squirrel-cage rotor.
Transformer
Second-degree burn.
A device used to store electrical energy.

8. At what rate should mouth-to-mouth resuscitation be applied?
The chest should rise or inflate.
12 to 15 times a minute.
Lower current and higher voltage
Provides single-phase power to smaller loads such as lights - heaters - etc.

9. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
75 turns.
It provides good speed control.
A device used to store electrical energy.

10. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
5:1.
Circuit Breaker.
600 volts.

11. High voltage is used to transmit power over long distances...
Inductance.
75 turns.
Short-circuited after power has been removed.
Because less current flowing at high voltage causes less line loss per kilowatt.

12. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
60 Hertz
Draw less current.
7 -630 volts.
Reverse any two-phase leads.

13. 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?
Lower current and higher voltage.
7 -630 volts.
600 volts.
They must be installed at least 7 feet above the ground.

14. 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?
150 turns.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
15 feet off the ground.
480 volts.

15. Alternating current may be defined as...
Stator windings.
Clamp-on ammeter.
Current that changes constantly in magnitude and periodically in direction.
Four times less than that of the secondary.

16. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
3 -979 Volts.
A step-up transformer.
Potential transformer.
It provides good speed control.

17. What is the danger when working around capacitors?
An electrical shock hazard may exist.
7 -630 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
100 volts.

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

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19. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
At the source transformer.
Second-degree burn.
Four times less than that of the secondary.
A step-up transformer.

20. Current that changes periodically in direction is...
Shunted and taped
25 feet.
Alternating current.
75 turns.

21. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Squirrel-cage induction motor.
Two speeds
H terminals.
It provides good speed control.

22. The property of an electrical circuit that opposes any change in voltage is called...
Nearly constant.
Capacitance.
Continuous.
Draw less current.

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.
Nearly constant.
Carotid pulse - which is located in the neck next to the Adam's apple.
Zero amps.

24. All transformers step voltage up or down by...
200 volts AC.
Inductance.
The motor rotation is reversed.
Reverse any two-phase leads.

25. Current in an AC circuit may be measured by...
Isolation transformer.
Clamp-on ammeter.
They must be installed at least 7 feet above the ground.
Provides single-phase power to smaller loads such as lights - heaters - etc.

26. Three-phase AC underground cables must be provided with overcurrent protection using a...
Kilovolt ampere (KVA).
Circuit Breaker.
The current will read zero.
Current that changes constantly in magnitude and periodically in direction.

27. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
The chest should rise or inflate.
Grounded phase and ground fault devices were not operating.
Squirrel-cage rotor.
3 -979 Volts.

28. The size of a transformer is measured in...
Potential transformer.
Zero amps.
Kilovolt ampere (KVA).
5:1

29. When not connected to a load - the secondary leads of a current transformer should be...
H terminals.
Shunted and taped
Larger than that found in the primary winding.
Circuit Breaker.

30. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
They should be made by the same manufacturer.
5:1.
X.

31. What type of 3-phase AC motor is used most often around a mine?
Inductance.
75 turns.
Squirrel-cage induction motor.
Kilovolt ampere (KVA).

32. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
It provides good speed control.
Continuous.
Two speeds
The motor rotation is reversed.

33. 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.
Cut around clothing that has adhered to the burned area.
Reverse its rotation.
Zero amps.

34. A transformer with a 1:1 ratio is usually a (an)...
15 feet off the ground.
Isolation transformer.
Current changing constantly in magnitude and periodically in direction.
Reverse any two-phase leads.

35. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Capacitance.
Because less current flowing at high voltage causes less line loss per kilowatt.
Larger than that found in the primary winding.
The capacitors should be discharged.

36. Not a symptom of electrical shock?.
Cut around clothing that has adhered to the burned area.
Hyperventilation.
Reverse its rotation.
Second-degree burn.

37. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Kilovolt ampere (KVA).
800 volts.
No.6 AWG.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

38. The transformer used only to measure voltage is a...
Potential transformer.
A device used to store electrical energy.
Inductance.
Reverse any two-phase leads.

39. 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...
Isolation transformer.
Tied together
They must be installed at least 7 feet above the ground.
Carotid pulse - which is located in the neck next to the Adam's apple.

40. 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.
They must be installed at least 7 feet above the ground.
277 volts.
Short-circuited after power has been removed.

41. 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.
It provides good speed control.
Squirrel-cage induction motor.
Transformers.

42. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Hyperventilation.
2000 watts
Allow for metering voltage and Current.
Continuous.

43. Where should grounding resistors be located?
200 volts AC.
At the source transformer.
Grounded phase and ground fault devices were not operating.
Larger than that found in the primary winding.

44. 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?
200 volts AC.
15 feet off the ground.
12 to 15 times a minute.
600 volts.

45. A solenoid coil is...
Inductance.
An electromagnet.
600 volts.
Squirrel-cage induction motor.

46. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Squirrel-cage induction motor.
A grounding resistor.
Alternating current.
Circuit Breaker.

47. Current transformers - or CT's - are used to...
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.
Squirrel-cage induction motor.
Transformer

48. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
Hyperventilation.
12 to 15 times a minute.
Lower current and higher voltage

49. Not true about AC power?
The chest should rise or inflate.
It provides good speed control.
60 cycles per second (60 Hertz).
Draw less current.

50. What type motor is a wound-rotor induction motor?
The motor rotation is reversed.
Circuit Breaker.
Transformer
A.C.