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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 speed of an alternating current - squirrel-cage induction motor is...
Current changing constantly in magnitude and periodically in direction.
Cut around clothing that has adhered to the burned area.
Nearly constant.
An electromagnet.

2. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
5:1
X.
Second-degree burn.
Four times less than that of the secondary.

3. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
They should be made by the same manufacturer.
Four times less than that of the secondary.
Kilovolt ampere (KVA).
X.

4. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Lower current and higher voltage
Current changing constantly in magnitude and periodically in direction.
1 amp.

5. Not a symptom of electrical shock?.
2000 watts
Hyperventilation.
An electrical shock hazard may exist.
Current changing constantly in magnitude and periodically in direction.

6. The secondary windings on a 10:1 step-down transformer will have a wire size...
100 volts.
Larger than that found in the primary winding.
At least two phases
The motor rotation is reversed.

7. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Shunted and taped

8. What steps up or steps down AC voltage?
Squirrel-cage rotor.
2000 watts
7 -630 volts.
Transformer

9. How should clothing be removed from a burn?
Two speeds
2000 watts
Transformers.
Cut around clothing that has adhered to the burned area.

10. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Grounded phase and ground fault devices were not operating.
A grounding resistor.
At least two phases
Second-degree burn.

11. A burn causing a blister is classified as a...
Second-degree burn.
150 turns.
Alternating current.
100 volts.

12. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
Kilovolt ampere (KVA).
At the source transformer.
Carotid pulse - which is located in the neck next to the Adam's apple.

13. A wound-rotor induction motor has all the following EXCEPT...
7 -630 volts.
60 cycles per second (60 Hertz).
5:1
Squirrel-cage rotor.

14. 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?
Reverse any two-phase leads.
Isolation transformer.
600 volts.
Allow for metering voltage and Current.

15. 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
Check to make sure that the victim is not still in contact with the electricity.
100 volts.
Current changing constantly in magnitude and periodically in direction.

16. A control power transformer...
Isolation transformer.
7 -630 volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Transformer

17. Alternating current may be defined as...
75 turns.
Current that changes constantly in magnitude and periodically in direction.
The motor rotation is reversed.
Provides single-phase power to smaller loads such as lights - heaters - etc.

18. 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?
Reverse any two-phase leads.
Stator windings.
Carotid pulse - which is located in the neck next to the Adam's apple.
800 volts.

19. What should the duty rating of a grounding resistor be?
Squirrel-cage rotor.
Draw less current.
Full-load - three-phase voltage.
Continuous.

20. A transformer has a primary voltage of 2 -800 volts and a secondary reading of 140 volts. If there are 2000 turns on the primary - how many turns are on the secondary?
Grounded phase and ground fault devices were not operating.
100 turns.
No.6 AWG.
3 -979 Volts.

21. Current transformers - or CT's - are used to...
An electrical shock hazard may exist.
Shunted and taped
Grounded phase and ground fault devices were not operating.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

22. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
7 -630 volts.
Zero amps.
277 volts.
600 volts.

23. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
100 volts.
75 turns.
Grounded phase and ground fault devices were not operating.
Provides single-phase power to smaller loads such as lights - heaters - etc.

24. 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?
The current will read zero.
Electro-magnetism for their operation.
No.6 AWG.
150 turns.

25. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Transformers.
A step-up transformer.
Continuous.
Current changing constantly in magnitude and periodically in direction.

26. The standard frequency of power supplied by the power company is...
Two speeds
200 volts AC.
Lower current and higher voltage.
60 cycles per second (60 Hertz).

27. At what rate should mouth-to-mouth resuscitation be applied?
600 volts.
12 to 15 times a minute.
60 Hertz
Full-load - three-phase voltage.

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

29. High voltage is used to transmit power over long distances...
At least two phases
Because less current flowing at high voltage causes less line loss per kilowatt.
Squirrel-cage rotor.
Transformer

30. What is the danger when working around capacitors?
The motor rotation is reversed.
An electrical shock hazard may exist.
At the source transformer.
Tied together

31. Current that changes periodically in direction is...
Alternating current.
Inductance.
Squirrel-cage rotor.
Inductance.

32. What type motor is a wound-rotor induction motor?
Four times less than that of the secondary.
A.C.
Isolation transformer.
Continuous.

33. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
A grounding resistor.
2000 watts
Transformer
7 -630 volts.

34. What type of 3-phase AC motor is used most often around a mine?
No.6 AWG.
Squirrel-cage induction motor.
Current that changes constantly in magnitude and periodically in direction.
Capacitance.

35. All transformers step voltage up or down by...
60 Hertz
Potential transformer.
Inductance.
A device used to store electrical energy.

36. The main function of CT's and PT's on a main substation is to...
The current will read zero.
Allow for metering voltage and Current.
Kilovolt ampere (KVA).
75 turns.

37. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
An electrical shock hazard may exist.
They should be made by the same manufacturer.
2000 watts
No.6 AWG.

38. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Zero amps.
12 to 15 times a minute.
Cut around clothing that has adhered to the burned area.

39. Not an acceptable method for the installations of surface transformers?
Draw less current.
2000 watts
They must be installed at least 7 feet above the ground.
Draw less current.

40. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse any two-phase leads.
Circuit Breaker.
3 -979 Volts.
Reverse its rotation.

41. Where should grounding resistors be located?
Short-circuited after power has been removed.
At the source transformer.
Stator windings.
5:1

42. The property of an electrical circuit that opposes any change in voltage is called...
Transformers.
Alternating current.
Capacitance.
Clamp-on ammeter.

43. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Full-load - three-phase voltage.
25 feet.
Current changing constantly in magnitude and periodically in direction.
277 volts.

44. The transformer used only to measure voltage is a...
Transformers.
A.C.
Derive a neutral for grounding purposes.
Potential transformer.

45. The property of an electric circuit that opposes any change in current is called...
Continuous.
Alternating current.
25 feet.
Inductance.

46. A transformer has a primary voltage of 2 -400 volts and a secondary reading of 120 volts. If there are 1 -500 turns on the primary - how many turns are on the secondary?
75 turns.
Two speeds
A device used to store electrical energy.
Carotid pulse - which is located in the neck next to the Adam's apple.

47. 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...
The motor rotation is reversed.
Draw less current.
480 volts.
X.

48. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
It provides good speed control.
Second-degree burn.
Squirrel-cage rotor.

49. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Hyperventilation.
Transformer
2000 watts
They should be made by the same manufacturer.

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