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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. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
3 -979 Volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
It provides good speed control.
Tied together

2. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
277 volts.
Lower current and higher voltage.
A step-up transformer.
75 turns.

3. The standard frequency of alternating current used at a mine is...
Full-load - three-phase voltage.
60 Hertz
100 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

4. 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.
Carotid pulse - which is located in the neck next to the Adam's apple.
Nearly constant.
100 volts.

5. 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.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Clamp-on ammeter.
Current changing constantly in magnitude and periodically in direction.

6. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Disconnect the frame-grounding conductor.
1 amp.
Provides single-phase power to smaller loads such as lights - heaters - etc.
They should be made by the same manufacturer.

7. 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?
Squirrel-cage rotor.
600 volts.
The sum of the two capacitors.
No.6 AWG.

8. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
Capacitance.
Carotid pulse - which is located in the neck next to the Adam's apple.
Squirrel-cage rotor.

9. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The motor rotation is reversed.
At least two phases
Inductance.
Potential transformer.

10. 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...
Full-load - three-phase voltage.
Second-degree burn.
Disconnect the frame-grounding conductor.
Draw less current.

11. What type motor is a wound-rotor induction motor?
Electro-magnetism for their operation.
Four times less than that of the secondary.
They must be installed at least 7 feet above the ground.
A.C.

12. A burn causing a blister is classified as a...
Because less current flowing at high voltage causes less line loss per kilowatt.
Second-degree burn.
2000 watts
Transformer

13. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Potential transformer.
Current that changes constantly in magnitude and periodically in direction.
Two speeds

14. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
X.
Short-circuited after power has been removed.
The current will read zero.
Full-load - three-phase voltage.

15. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
A device used to store electrical energy.
Grounded phase and ground fault devices were not operating.
75 turns.
No.6 AWG.

16. A solenoid coil is...
An electromagnet.
X.
600 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.

17. 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.
Disconnect the frame-grounding conductor.
60 cycles per second (60 Hertz).
Squirrel-cage induction motor.

18. The purpose of a zig-zag transformer is to...
The chest should rise or inflate.
Derive a neutral for grounding purposes.
Shunted and taped
Current changing constantly in magnitude and periodically in direction.

19. Not a symptom of electrical shock?.
5:1.
60 cycles per second (60 Hertz).
Circuit Breaker.
Hyperventilation.

20. The property of an electric circuit that opposes any change in current is called...
Inductance.
Hyperventilation.
Current that changes constantly in magnitude and periodically in direction.
Zero amps.

21. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
277 volts.
Draw less current.
The motor rotation is reversed.
3 -979 Volts.

22. A transformer with a 1:1 ratio is usually a (an)...
Clamp-on ammeter.
Isolation transformer.
60 Hertz
Short-circuited after power has been removed.

23. 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...
Transformer
3 -979 Volts.
X.
Tied together

24. Where should grounding resistors be located?
At the source transformer.
Electro-magnetism for their operation.
Carotid pulse - which is located in the neck next to the Adam's apple.
The current will read zero.

25. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
277 volts.
60 cycles per second (60 Hertz).
Continuous.

26. 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?
They should be made by the same manufacturer.
Shunted and taped
150 turns.
Current changing constantly in magnitude and periodically in direction.

27. The size of a transformer is measured in...
Kilovolt ampere (KVA).
Isolation transformer.
Inductance.
The current will read zero.

28. Current transformers - or CT's - are used to...
H terminals.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Second-degree burn.
25 feet.

29. 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...
25 feet.
The motor rotation is reversed.
100 volts.
3 -979 Volts.

30. What steps up or steps down AC voltage?
Stator windings.
Second-degree burn.
Short-circuited after power has been removed.
Transformer

31. What should the duty rating of a grounding resistor be?
Continuous.
Draw less current.
480 volts.
75 turns.

32. The standard frequency of power supplied by the power company is...
277 volts.
Squirrel-cage rotor.
Allow for metering voltage and Current.
60 cycles per second (60 Hertz).

33. 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?
H terminals.
An electrical shock hazard may exist.
Full-load - three-phase voltage.
3 -979 Volts.

34. A control power transformer...
It provides good speed control.
Larger than that found in the primary winding.
H terminals.
Provides single-phase power to smaller loads such as lights - heaters - etc.

35. Which of the following does a squirrel cage induction motor have?
Stator windings.
Current that changes constantly in magnitude and periodically in direction.
75 turns.
600 volts.

36. Compared to the secondary of a loaded - step-down transformer - the primary has...
Four times less than that of the secondary.
100 turns.
Lower current and higher voltage
75 turns.

37. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Electro-magnetism for their operation.
Carotid pulse - which is located in the neck next to the Adam's apple.
15 feet off the ground.
Because less current flowing at high voltage causes less line loss per kilowatt.

38. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
The sum of the two capacitors.
Derive a neutral for grounding purposes.
1 amp.

39. Three-phase AC underground cables must be provided with overcurrent protection using a...
Cut around clothing that has adhered to the burned area.
Inductance.
600 volts.
Circuit Breaker.

40. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
Tied together
Continuous.
Short-circuited after power has been removed.

41. AC voltage is raised or lowered by means of...
They must be installed at least 7 feet above the ground.
Electro-magnetism for their operation.
Transformers.
15 feet off the ground.

42. All transformers step voltage up or down by...
Current that changes constantly in magnitude and periodically in direction.
Inductance.
Second-degree burn.
100 volts.

43. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Current that changes constantly in magnitude and periodically in direction.
480 volts.
2000 watts
A grounding resistor.

44. The primary leads of a single-phase transformer should be connected to the...
The motor rotation is reversed.
277 volts.
H terminals.
Isolation transformer.

45. 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?
100 volts.
75 turns.
12 to 15 times a minute.
600 volts.

46. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Second-degree burn.
Two speeds
Allow for metering voltage and Current.
Reverse its rotation.

47. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
2000 watts
12 to 15 times a minute.
5:1

48. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
75 turns.
Short-circuited after power has been removed.
Check to make sure that the victim is not still in contact with the electricity.

49. Current in an AC circuit may be measured by...
Inductance.
A.C.
Clamp-on ammeter.
600 volts.

50. Not true about AC power?
It provides good speed control.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
25 feet.
Derive a neutral for grounding purposes.