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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. Find the turns ratio of a single-phase transformer with the following values: Primary power of 10 KW - secondary current of 200 amps - and primary voltage of 250 volts.
3 -979 Volts.
5:1.
They must be installed at least 7 feet above the ground.
Inductance.

2. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
7 -630 volts.
Squirrel-cage induction motor.
Isolation transformer.
No.6 AWG.

3. The standard frequency of alternating current used at a mine is...
480 volts.
25 feet.
60 Hertz
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

4. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Capacitance.
277 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

5. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Kilovolt ampere (KVA).
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Full-load - three-phase voltage.
Larger than that found in the primary winding.

6. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
5:1
Squirrel-cage rotor.
Electro-magnetism for their operation.

7. 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?
3 -979 Volts.
At least two phases
150 turns.
Current changing constantly in magnitude and periodically in direction.

8. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Inductance.
They should be made by the same manufacturer.
At the source transformer.
Short-circuited after power has been removed.

9. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
The chest should rise or inflate.
H terminals.
Electro-magnetism for their operation.

10. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
5:1.
277 volts.
No.6 AWG.
Lower current and higher voltage

11. If any two-phase wires are reversed on a three-phase motor - the motor will...
The chest should rise or inflate.
They should be made by the same manufacturer.
Stator windings.
Reverse its rotation.

12. 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?
100 turns.
75 turns.
Reverse its rotation.
Inductance.

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

14. Current that changes periodically in direction is...
600 volts.
15 feet off the ground.
Alternating current.
A.C.

15. What is the danger when working around capacitors?
Cut around clothing that has adhered to the burned area.
A step-up transformer.
100 turns.
An electrical shock hazard may exist.

16. AC voltage is raised or lowered by means of...
Potential transformer.
Transformers.
X.
Lower current and higher voltage.

17. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Transformer
25 feet.
Potential transformer.

18. Not a symptom of electrical shock?.
1 amp.
A step-up transformer.
Two speeds
Hyperventilation.

19. What type motor is a wound-rotor induction motor?
A.C.
X.
Kilovolt ampere (KVA).
480 volts.

20. The primary function of a power transformer is to provide...
Because less current flowing at high voltage causes less line loss per kilowatt.
An electromagnet.
Full-load - three-phase voltage.
Four times less than that of the secondary.

21. What is a capacitor?
They must be installed at least 7 feet above the ground.
600 volts.
A grounding resistor.
A device used to store electrical energy.

22. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
75 turns.
5:1.
Lower current and higher voltage.
2000 watts

23. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
Zero amps.
Current changing constantly in magnitude and periodically in direction.
7 -630 volts.

24. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
An electromagnet.
100 volts.
The chest should rise or inflate.

25. The primary leads of a single-phase transformer should be connected to the...
It provides good speed control.
200 volts AC.
Capacitance.
H terminals.

26. All transformers step voltage up or down by...
A grounding resistor.
25 feet.
Inductance.
12 to 15 times a minute.

27. The transformer used only to measure voltage is a...
Potential transformer.
60 cycles per second (60 Hertz).
Derive a neutral for grounding purposes.
Capacitance.

28. Where should grounding resistors be located?
1 amp.
100 volts.
Clamp-on ammeter.
At the source transformer.

29. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
They should be made by the same manufacturer.
They must be installed at least 7 feet above the ground.
75 turns.

30. Three-phase AC underground cables must be provided with overcurrent protection using a...
75 turns.
Full-load - three-phase voltage.
Circuit Breaker.
No.6 AWG.

31. 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?
480 volts.
5:1.
600 volts.
Capacitance.

32. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
7 -630 volts.
Disconnect the frame-grounding conductor.
At least two phases
15 feet off the ground.

33. 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?
1 amp.
Squirrel-cage induction motor.
200 volts AC.
They must be installed at least 7 feet above the ground.

34. At what rate should mouth-to-mouth resuscitation be applied?
Because less current flowing at high voltage causes less line loss per kilowatt.
Circuit Breaker.
12 to 15 times a minute.
A grounding resistor.

35. The property of an electric circuit that opposes any change in current is called...
Transformer
800 volts.
Inductance.
Second-degree burn.

36. The size of a transformer is measured in...
12 to 15 times a minute.
A device used to store electrical energy.
Kilovolt ampere (KVA).
They should be made by the same manufacturer.

37. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
They should be made by the same manufacturer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Four times less than that of the secondary.
7 -630 volts.

38. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Full-load - three-phase voltage.
150 turns.
The chest should rise or inflate.
The current will read zero.

39. The speed of an alternating current - squirrel-cage induction motor is...
A.C.
H terminals.
Nearly constant.
A device used to store electrical energy.

40. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
75 turns.
Cut around clothing that has adhered to the burned area.
Current changing constantly in magnitude and periodically in direction.
Two speeds

41. What is the first step to be followed in aiding a victim of electrical shock?
A device used to store electrical energy.
Check to make sure that the victim is not still in contact with the electricity.
An electrical shock hazard may exist.
Stator windings.

42. Compared to the secondary of a loaded - step-down transformer - the primary has...
Alternating current.
H terminals.
Lower current and higher voltage
Isolation transformer.

43. What should the duty rating of a grounding resistor be?
Continuous.
Cut around clothing that has adhered to the burned area.
Capacitance.
2000 watts

44. The property of an electrical circuit that opposes any change in voltage is called...
Lower current and higher voltage
Capacitance.
The current will read zero.
Check to make sure that the victim is not still in contact with the electricity.

45. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
X.
Provides single-phase power to smaller loads such as lights - heaters - etc.
75 turns.

46. A burn causing a blister is classified as a...
X.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
1 amp.
Second-degree burn.

47. The main function of CT's and PT's on a main substation is to...
A device used to store electrical energy.
Allow for metering voltage and Current.
Disconnect the frame-grounding conductor.
150 turns.

48. Define alternating current...
5:1.
Current changing constantly in magnitude and periodically in direction.
Squirrel-cage rotor.
5:1

49. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Grounded phase and ground fault devices were not operating.
1 amp.
Second-degree burn.
No.6 AWG.

50. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
100 turns.
7 -630 volts.
Reverse its rotation.
A step-up transformer.