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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. What is the first step to be followed in aiding a victim of electrical shock?
Transformer
Cut around clothing that has adhered to the burned area.
Continuous.
Check to make sure that the victim is not still in contact with the electricity.

2. 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.
An electrical shock hazard may exist.
The chest should rise or inflate.

3. A transformer with a 1:1 ratio is usually a (an)...
Cut around clothing that has adhered to the burned area.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Isolation transformer.
No.6 AWG.

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.
Alternating current.
480 volts.
Tied together

5. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Lower current and higher voltage.
The sum of the two capacitors.
Squirrel-cage induction motor.
Grounded phase and ground fault devices were not operating.

6. All transformers step voltage up or down by...
Draw less current.
Current that changes constantly in magnitude and periodically in direction.
100 volts.
Inductance.

7. 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.
An electrical shock hazard may exist.
Full-load - three-phase voltage.
The current will read zero.

8. How do you change the direction of a 3-phase AC motor?
Inductance.
Reverse any two-phase leads.
The motor rotation is reversed.
100 volts.

9. A burn causing a blister is classified as a...
Second-degree burn.
Clamp-on ammeter.
Larger than that found in the primary winding.
Kilovolt ampere (KVA).

10. What is the danger when working around capacitors?
Potential transformer.
7 -630 volts.
An electrical shock hazard may exist.
The sum of the two capacitors.

11. The transformer used only to measure voltage is a...
600 volts.
Potential transformer.
25 feet.
Reverse any two-phase leads.

12. 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?
Hyperventilation.
200 volts AC.
Squirrel-cage rotor.
800 volts.

13. 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.
200 volts AC.
5:1
Lower current and higher voltage

14. When not connected to a load - the secondary leads of a current transformer should be...
Four times less than that of the secondary.
Short-circuited after power has been removed.
Shunted and taped
Disconnect the frame-grounding conductor.

15. 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.
Reverse its rotation.
The current will read zero.
Capacitance.

16. Current in an AC circuit may be measured by...
An electromagnet.
Clamp-on ammeter.
Kilovolt ampere (KVA).
1 amp.

17. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
60 cycles per second (60 Hertz).
The current will read zero.
They should be made by the same manufacturer.
1 amp.

18. If any two-phase wires are reversed on a three-phase motor - the motor will...
60 cycles per second (60 Hertz).
Allow for metering voltage and Current.
12 to 15 times a minute.
Reverse its rotation.

19. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
60 cycles per second (60 Hertz).
Isolation transformer.
3 -979 Volts.

20. 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?
Current changing constantly in magnitude and periodically in direction.
Four times less than that of the secondary.
3 -979 Volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.

21. The standard frequency of power supplied by the power company is...
Short-circuited after power has been removed.
60 cycles per second (60 Hertz).
25 feet.
Circuit Breaker.

22. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Current changing constantly in magnitude and periodically in direction.
Grounded phase and ground fault devices were not operating.
Disconnect the frame-grounding conductor.
5:1.

23. What type of 3-phase AC motor is used most often around a mine?
200 volts AC.
Draw less current.
Continuous.
Squirrel-cage induction motor.

24. AC voltage is raised or lowered by means of...
Two speeds
Transformers.
At least two phases
Draw less current.

25. The primary function of a power transformer is to provide...
Alternating current.
2000 watts
Full-load - three-phase voltage.
Hyperventilation.

26. A solenoid coil is...
An electromagnet.
Alternating current.
Squirrel-cage induction motor.
Cut around clothing that has adhered to the burned area.

27. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
3 -979 Volts.
12 to 15 times a minute.
277 volts.
100 volts.

28. 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?
75 turns.
At least two phases
H terminals.
The motor rotation is reversed.

29. The primary leads of a single-phase transformer should be connected to the...
H terminals.
3 -979 Volts.
At least two phases
They should be made by the same manufacturer.

30. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Kilovolt ampere (KVA).
At least two phases
Zero amps.
100 volts.

31. The property of an electric circuit that opposes any change in current is called...
Draw less current.
Kilovolt ampere (KVA).
Inductance.
Stator windings.

32. The standard frequency of alternating current used at a mine is...
Grounded phase and ground fault devices were not operating.
Derive a neutral for grounding purposes.
60 Hertz
480 volts.

33. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Draw less current.
600 volts.
Inductance.

34. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
At least two phases
25 feet.
An electromagnet.

35. The size of a transformer is measured in...
12 to 15 times a minute.
Tied together
800 volts.
Kilovolt ampere (KVA).

36. Not true about AC power?
It provides good speed control.
Short-circuited after power has been removed.
Circuit Breaker.
Squirrel-cage induction motor.

37. Not a symptom of electrical shock?.
Short-circuited after power has been removed.
100 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
Hyperventilation.

38. 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?
Full-load - three-phase voltage.
Nearly constant.
Clamp-on ammeter.
75 turns.

39. Where should grounding resistors be located?
At the source transformer.
Hyperventilation.
5:1
2000 watts

40. 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...
Two speeds
Four times less than that of the secondary.
Tied together
Kilovolt ampere (KVA).

41. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
15 feet off the ground.
Allow for metering voltage and Current.
No.6 AWG.

42. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Continuous.
The current will read zero.
Shunted and taped

43. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
480 volts.
An electrical shock hazard may exist.
Transformer

44. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Carotid pulse - which is located in the neck next to the Adam's apple.
25 feet.
100 volts.
Capacitance.

45. High voltage is used to transmit power over long distances...
An electrical shock hazard may exist.
Reverse any two-phase leads.
Because less current flowing at high voltage causes less line loss per kilowatt.
Hyperventilation.

46. 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.
Reverse its rotation.
75 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.

47. Define alternating current...
2000 watts
75 turns.
Inductance.
Current changing constantly in magnitude and periodically in direction.

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

49. The property of an electrical circuit that opposes any change in voltage is called...
No.6 AWG.
15 feet off the ground.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Capacitance.

50. 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...
Transformer
Second-degree burn.
Provides single-phase power to smaller loads such as lights - heaters - etc.
100 volts.