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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...
Shunted and taped
Lower current and higher voltage.
Nearly constant.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

2. All transformers step voltage up or down by...
7 -630 volts.
277 volts.
No.6 AWG.
Inductance.

3. 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...
100 volts.
A.C.
At least two phases
Two speeds

4. What is the danger when working around capacitors?
200 volts AC.
Short-circuited after power has been removed.
Clamp-on ammeter.
An electrical shock hazard may exist.

5. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
Check to make sure that the victim is not still in contact with the electricity.
Larger than that found in the primary winding.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

6. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Potential transformer.
Transformer
25 feet.
Shunted and taped

7. 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.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
They should be made by the same manufacturer.
It provides good speed control.

8. High voltage is used to transmit power over long distances...
H terminals.
Full-load - three-phase voltage.
100 turns.
Because less current flowing at high voltage causes less line loss per kilowatt.

9. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
No.6 AWG.
Kilovolt ampere (KVA).
25 feet.
Zero amps.

10. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Second-degree burn.
The motor rotation is reversed.
Continuous.
Allow for metering voltage and Current.

11. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
600 volts.
7 -630 volts.
The sum of the two capacitors.

12. Compared to the secondary of a loaded - step-down transformer - the primary has...
They should be made by the same manufacturer.
Tied together
Lower current and higher voltage
100 volts.

13. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Reverse its rotation.
A.C.
The capacitors should be discharged.
Lower current and higher voltage.

14. Which of the following does a squirrel cage induction motor have?
3 -979 Volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
Carotid pulse - which is located in the neck next to the Adam's apple.
Stator windings.

15. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
1 amp.
100 turns.
The chest should rise or inflate.
Provides single-phase power to smaller loads such as lights - heaters - etc.

16. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A grounding resistor.
5:1
Grounded phase and ground fault devices were not operating.
75 turns.

17. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Continuous.
Full-load - three-phase voltage.
At least two phases

18. 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?
Zero amps.
Lower current and higher voltage
150 turns.
Squirrel-cage rotor.

19. What type of 3-phase AC motor is used most often around a mine?
Derive a neutral for grounding purposes.
Squirrel-cage induction motor.
Larger than that found in the primary winding.
15 feet off the ground.

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

21. The standard frequency of power supplied by the power company is...
Shunted and taped
A step-up transformer.
A grounding resistor.
60 cycles per second (60 Hertz).

22. 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...
3 -979 Volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The capacitors should be discharged.
Tied together

23. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Clamp-on ammeter.
Hyperventilation.
480 volts.
No.6 AWG.

24. 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.
Transformer
2000 watts
150 turns.

25. What is a capacitor?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
A device used to store electrical energy.
Electro-magnetism for their operation.
Lower current and higher voltage.

26. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Reverse any two-phase leads.
Kilovolt ampere (KVA).
Electro-magnetism for their operation.

27. A control power transformer...
Because less current flowing at high voltage causes less line loss per kilowatt.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Inductance.
1 amp.

28. The combined capacitance of two capacitors in parallel is...
A step-up transformer.
The motor rotation is reversed.
The sum of the two capacitors.
Allow for metering voltage and Current.

29. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Carotid pulse - which is located in the neck next to the Adam's apple.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Two speeds
Nearly constant.

30. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
2000 watts
7 -630 volts.
Capacitance.
Inductance.

31. 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?
480 volts.
75 turns.
5:1.
Four times less than that of the secondary.

32. Define alternating current...
60 cycles per second (60 Hertz).
Draw less current.
Current changing constantly in magnitude and periodically in direction.
Kilovolt ampere (KVA).

33. What type motor is a wound-rotor induction motor?
75 turns.
The sum of the two capacitors.
A.C.
Zero amps.

34. What steps up or steps down AC voltage?
They should be made by the same manufacturer.
Transformer
Draw less current.
Grounded phase and ground fault devices were not operating.

35. AC voltage is raised or lowered by means of...
600 volts.
Tied together
Transformers.
Inductance.

36. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Because less current flowing at high voltage causes less line loss per kilowatt.
Cut around clothing that has adhered to the burned area.

37. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
7 -630 volts.
12 to 15 times a minute.
A.C.

38. 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.
Circuit Breaker.
Grounded phase and ground fault devices were not operating.
Draw less current.

39. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
An electrical shock hazard may exist.
A.C.
3 -979 Volts.

40. 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...
Lower current and higher voltage
277 volts.
75 turns.
Draw less current.

41. What is the first step to be followed in aiding a victim of electrical shock?
Two speeds
Four times less than that of the secondary.
Check to make sure that the victim is not still in contact with the electricity.
Continuous.

42. 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...
277 volts.
800 volts.
Draw less current.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

43. The transformer used only to measure voltage is a...
They must be installed at least 7 feet above the ground.
Capacitance.
Potential transformer.
480 volts.

44. 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.
Tied together
Provides single-phase power to smaller loads such as lights - heaters - etc.
Short-circuited after power has been removed.

45. How should clothing be removed from a burn?
At the source transformer.
Cut around clothing that has adhered to the burned area.
Hyperventilation.
800 volts.

46. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Inductance.
At least two phases
Larger than that found in the primary winding.

47. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Check to make sure that the victim is not still in contact with the electricity.
Larger than that found in the primary winding.
7 -630 volts.
Grounded phase and ground fault devices were not operating.

48. Not an acceptable method for the installations of surface transformers?
Nearly constant.
12 to 15 times a minute.
Stator windings.
They must be installed at least 7 feet above the ground.

49. 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?
At least two phases
480 volts.
75 turns.
Zero amps.

50. How do you change the direction of a 3-phase AC motor?
12 to 15 times a minute.
Reverse any two-phase leads.
Four times less than that of the secondary.
Second-degree burn.