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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. 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?
An electrical shock hazard may exist.
Circuit Breaker.
100 turns.
5:1.

2. Current that changes periodically in direction is...
The motor rotation is reversed.
It provides good speed control.
Lower current and higher voltage
Alternating current.

3. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Four times less than that of the secondary.
Nearly constant.
Lower current and higher voltage
Two speeds

4. 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.
They should be made by the same manufacturer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Alternating current.

5. 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?
5:1.
277 volts.
200 volts AC.
480 volts.

6. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Reverse any two-phase leads.
600 volts.
Lower current and higher voltage

7. 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 turns.
100 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

8. Not true about AC power?
It provides good speed control.
7 -630 volts.
Lower current and higher voltage.
Tied together

9. What type of 3-phase AC motor is used most often around a mine?
2000 watts
Squirrel-cage induction motor.
The sum of the two capacitors.
Second-degree burn.

10. When not connected to a load - the secondary leads of a current transformer should be...
100 turns.
The current will read zero.
480 volts.
Shunted and taped

11. Which of the following does a squirrel cage induction motor have?
Stator windings.
2000 watts
Reverse its rotation.
Squirrel-cage rotor.

12. Not an acceptable method for the installations of surface transformers?
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.
Kilovolt ampere (KVA).
Disconnect the frame-grounding conductor.

13. Define alternating current...
Draw less current.
Derive a neutral for grounding purposes.
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.

14. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Alternating current.
Draw less current.
No.6 AWG.

15. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
2000 watts
15 feet off the ground.
Stator windings.

16. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Disconnect the frame-grounding conductor.
Hyperventilation.
X.
480 volts.

17. 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...
Draw less current.
The capacitors should be discharged.
60 Hertz
277 volts.

18. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
The current will read zero.
Current that changes constantly in magnitude and periodically in direction.
100 volts.

19. Compared to the secondary of a loaded - step-down transformer - the primary has...
Two speeds
12 to 15 times a minute.
Potential transformer.
Lower current and higher voltage.

20. 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.
75 turns.
They must be installed at least 7 feet above the ground.
The sum of the two capacitors.

21. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
12 to 15 times a minute.
3 -979 Volts.
X.
The capacitors should be discharged.

22. The standard frequency of alternating current used at a mine is...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Nearly constant.
60 Hertz
Current changing constantly in magnitude and periodically in direction.

23. What steps up or steps down AC voltage?
The motor rotation is reversed.
Disconnect the frame-grounding conductor.
An electromagnet.
Transformer

24. If any two-phase wires are reversed on a three-phase motor - the motor will...
Because less current flowing at high voltage causes less line loss per kilowatt.
Reverse its rotation.
Inductance.
Draw less current.

25. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Capacitance.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Continuous.
Grounded phase and ground fault devices were not operating.

26. The primary leads of a single-phase transformer should be connected to the...
Electro-magnetism for their operation.
H terminals.
Squirrel-cage rotor.
An electromagnet.

27. What should the duty rating of a grounding resistor be?
Squirrel-cage rotor.
Hyperventilation.
Inductance.
Continuous.

28. The speed of an alternating current - squirrel-cage induction motor is...
Full-load - three-phase voltage.
Second-degree burn.
200 volts AC.
Nearly constant.

29. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Carotid pulse - which is located in the neck next to the Adam's apple.
Disconnect the frame-grounding conductor.
480 volts.
Current that changes constantly in magnitude and periodically in direction.

30. 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 rotor.
Two speeds
Shunted and taped
H terminals.

31. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Inductance.
Capacitance.
Tied together

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

33. AC voltage is raised or lowered by means of...
Cut around clothing that has adhered to the burned area.
150 turns.
2000 watts
Transformers.

34. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
5:1
An electrical shock hazard may exist.
The capacitors should be discharged.

35. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The motor rotation is reversed.
Reverse any two-phase leads.
The chest should rise or inflate.
Check to make sure that the victim is not still in contact with the electricity.

36. A solenoid coil is...
Current changing constantly in magnitude and periodically in direction.
An electromagnet.
X.
Transformers.

37. A burn causing a blister is classified as a...
A grounding resistor.
7 -630 volts.
Second-degree burn.
They must be installed at least 7 feet above the ground.

38. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
100 turns.
Disconnect the frame-grounding conductor.
Larger than that found in the primary winding.

39. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
Second-degree burn.
The current will read zero.
Stator windings.

40. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Hyperventilation.
The motor rotation is reversed.
H terminals.
The chest should rise or inflate.

41. The transformer used only to measure voltage is a...
Disconnect the frame-grounding conductor.
7 -630 volts.
Potential transformer.
Allow for metering voltage and Current.

42. What is a capacitor?
The capacitors should be discharged.
It provides good speed control.
The motor rotation is reversed.
A device used to store electrical energy.

43. 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?
Shunted and taped
The chest should rise or inflate.
75 turns.
100 turns.

44. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
2000 watts
25 feet.
5:1.
Squirrel-cage rotor.

45. Not a symptom of electrical shock?.
Alternating current.
Hyperventilation.
100 volts.
Shunted and taped

46. The property of an electric circuit that opposes any change in current is called...
Squirrel-cage rotor.
No.6 AWG.
Allow for metering voltage and Current.
Inductance.

47. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Zero amps.
Second-degree burn.
Reverse any two-phase leads.
No.6 AWG.

48. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
200 volts AC.
A step-up transformer.
Disconnect the frame-grounding conductor.
A.C.

49. Current transformers - or CT's - are used to...
Circuit Breaker.
Inductance.
Tied together
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

50. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
12 to 15 times a minute.
Kilovolt ampere (KVA).
Continuous.
The current will read zero.