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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. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
The chest should rise or inflate.
277 volts.
Shunted and taped
5:1

2. What type of 3-phase AC motor is used most often around a mine?
Capacitance.
Because less current flowing at high voltage causes less line loss per kilowatt.
Squirrel-cage induction motor.
Hyperventilation.

3. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
H terminals.
Inductance.
Potential transformer.
They should be made by the same manufacturer.

4. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
The sum of the two capacitors.
Transformers.
Two speeds

5. The size of a transformer is measured in...
Potential transformer.
Lower current and higher voltage.
Hyperventilation.
Kilovolt ampere (KVA).

6. 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?
Transformers.
An electromagnet.
100 turns.
Lower current and higher voltage

7. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
The capacitors should be discharged.
No.6 AWG.
Disconnect the frame-grounding conductor.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

8. 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.
Stator windings.
150 turns.
100 turns.

9. Find the turns ratio of a single-phase transformer with the following values: Primary power of 5KW - secondary current of 100 amps - and primary voltage of 250 volts.
5:1
No.6 AWG.
2000 watts
It provides good speed control.

10. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Carotid pulse - which is located in the neck next to the Adam's apple.
100 turns.
277 volts.

11. 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.
5:1.
Larger than that found in the primary winding.
60 Hertz
150 turns.

12. The transformer used only to measure voltage is a...
Lower current and higher voltage.
They must be installed at least 7 feet above the ground.
Potential transformer.
Continuous.

13. The primary leads of a single-phase transformer should be connected to the...
They must be installed at least 7 feet above the ground.
H terminals.
Draw less current.
60 cycles per second (60 Hertz).

14. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
X.
Tied together
Hyperventilation.
A step-up transformer.

15. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
The chest should rise or inflate.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
At least two phases

16. How do you change the direction of a 3-phase AC motor?
Full-load - three-phase voltage.
Reverse any two-phase leads.
100 volts.
At least two phases

17. What is the first step to be followed in aiding a victim of electrical shock?
Hyperventilation.
An electrical shock hazard may exist.
A step-up transformer.
Check to make sure that the victim is not still in contact with the electricity.

18. What is the danger when working around capacitors?
They must be installed at least 7 feet above the ground.
Reverse its rotation.
An electrical shock hazard may exist.
Electro-magnetism for their operation.

19. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
2000 watts
Inductance.
Larger than that found in the primary winding.

20. What is a capacitor?
An electrical shock hazard may exist.
600 volts.
A device used to store electrical energy.
75 turns.

21. Current transformers - or CT's - are used to...
Tied together
15 feet off the ground.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Continuous.

22. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
200 volts AC.
The chest should rise or inflate.
100 turns.
Larger than that found in the primary winding.

23. Not a symptom of electrical shock?.
100 turns.
Hyperventilation.
Cut around clothing that has adhered to the burned area.
Larger than that found in the primary winding.

24. 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...
Draw less current.
Tied together
They should be made by the same manufacturer.
Continuous.

25. Compared to the secondary of a loaded - step-down transformer - the primary has...
Reverse its rotation.
Allow for metering voltage and Current.
100 turns.
Lower current and higher voltage.

26. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
At the source transformer.
5:1
Carotid pulse - which is located in the neck next to the Adam's apple.
Short-circuited after power has been removed.

27. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
X.
200 volts AC.
3 -979 Volts.

28. The standard frequency of power supplied by the power company is...
The sum of the two capacitors.
Grounded phase and ground fault devices were not operating.
277 volts.
60 cycles per second (60 Hertz).

29. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Capacitance.
A grounding resistor.
It provides good speed control.
480 volts.

30. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
Two speeds
Inductance.
Inductance.

31. 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?
X.
Grounded phase and ground fault devices were not operating.
800 volts.
Nearly constant.

32. 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?
Electro-magnetism for their operation.
600 volts.
Squirrel-cage induction motor.
1 amp.

33. Where should grounding resistors be located?
100 volts.
At least two phases
At the source transformer.
Isolation transformer.

34. 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 motor rotation is reversed.
The chest should rise or inflate.
Tied together

35. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Cut around clothing that has adhered to the burned area.
15 feet off the ground.
800 volts.
7 -630 volts.

36. The primary function of a power transformer is to provide...
Check to make sure that the victim is not still in contact with the electricity.
The motor rotation is reversed.
Full-load - three-phase voltage.
800 volts.

37. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
75 turns.
Grounded phase and ground fault devices were not operating.
Continuous.
The current will read zero.

38. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Isolation transformer.
The sum of the two capacitors.
The capacitors should be discharged.
25 feet.

39. What should the duty rating of a grounding resistor be?
150 turns.
Continuous.
The current will read zero.
Check to make sure that the victim is not still in contact with the electricity.

40. Alternating current may be defined as...
Lower current and higher voltage
15 feet off the ground.
Reverse its rotation.
Current that changes constantly in magnitude and periodically in direction.

41. A control power transformer...
Continuous.
The current will read zero.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Carotid pulse - which is located in the neck next to the Adam's apple.

42. High voltage is used to transmit power over long distances...
They must be installed at least 7 feet above the ground.
Potential transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.
Electro-magnetism for their operation.

43. What steps up or steps down AC voltage?
7 -630 volts.
200 volts AC.
Grounded phase and ground fault devices were not operating.
Transformer

44. Current that changes periodically in direction is...
Grounded phase and ground fault devices were not operating.
Shunted and taped
The capacitors should be discharged.
Alternating current.

45. Not true about AC power?
It provides good speed control.
100 volts.
The current will read zero.
Shunted and taped

46. The combined capacitance of two capacitors in parallel is...
Zero amps.
Stator windings.
Two speeds
The sum of the two capacitors.

47. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Four times less than that of the secondary.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Nearly constant.

48. A solenoid coil is...
An electromagnet.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
It provides good speed control.
Zero amps.

49. Current in an AC circuit may be measured by...
At the source transformer.
Clamp-on ammeter.
Current changing constantly in magnitude and periodically in direction.
Grounded phase and ground fault devices were not operating.

50. 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.
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.
5:1