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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 steps up or steps down AC voltage?
Second-degree burn.
1 amp.
Transformer
75 turns.

2. The secondary windings on a 10:1 step-down transformer will have a wire size...
They should be made by the same manufacturer.
The capacitors should be discharged.
Larger than that found in the primary winding.
Inductance.

3. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
100 volts.
Four times less than that of the secondary.
12 to 15 times a minute.
They must be installed at least 7 feet above the ground.

4. The size of a transformer is measured in...
60 cycles per second (60 Hertz).
Transformer
Four times less than that of the secondary.
Kilovolt ampere (KVA).

5. Current in an AC circuit may be measured by...
Alternating current.
7 -630 volts.
Clamp-on ammeter.
An electrical shock hazard may exist.

6. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
3 -979 Volts.
Two speeds
At the source transformer.
The capacitors should be discharged.

7. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Grounded phase and ground fault devices were not operating.
Stator windings.
The chest should rise or inflate.

8. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Cut around clothing that has adhered to the burned area.
25 feet.
277 volts.
Potential transformer.

9. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Cut around clothing that has adhered to the burned area.
The capacitors should be discharged.
Grounded phase and ground fault devices were not operating.
Four times less than that of the secondary.

10. Which of the following does a squirrel cage induction motor have?
Current changing constantly in magnitude and periodically in direction.
Because less current flowing at high voltage causes less line loss per kilowatt.
Stator windings.
7 -630 volts.

11. A solenoid coil is...
Four times less than that of the secondary.
An electromagnet.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Circuit Breaker.

12. Compared to the secondary of a loaded - step-down transformer - the primary has...
Disconnect the frame-grounding conductor.
Lower current and higher voltage
Stator windings.
The chest should rise or inflate.

13. What is the first step to be followed in aiding a victim of electrical shock?
277 volts.
Check to make sure that the victim is not still in contact with the electricity.
Kilovolt ampere (KVA).
Isolation transformer.

14. The standard frequency of power supplied by the power company is...
Circuit Breaker.
1 amp.
60 cycles per second (60 Hertz).
A step-up transformer.

15. AC voltage is raised or lowered by means of...
60 Hertz
H terminals.
Transformers.
Grounded phase and ground fault devices were not operating.

16. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Clamp-on ammeter.
Lower current and higher voltage.
Draw less current.
2000 watts

17. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
5:1
The sum of the two capacitors.
Squirrel-cage rotor.

18. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
Tied together
A step-up transformer.
They should be made by the same manufacturer.

19. The property of an electric circuit that opposes any change in current is called...
Inductance.
3 -979 Volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
15 feet off the ground.

20. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Zero amps.
A.C.
They should be made by the same manufacturer.

21. All transformers step voltage up or down by...
A.C.
Inductance.
Zero amps.
Continuous.

22. 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?
X.
100 turns.
Hyperventilation.
Provides single-phase power to smaller loads such as lights - heaters - etc.

23. 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?
Lower current and higher voltage.
3 -979 Volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Disconnect the frame-grounding conductor.

24. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Stator windings.
5:1
H terminals.
The current will read zero.

25. What should the duty rating of a grounding resistor be?
Inductance.
Transformer
H terminals.
Continuous.

26. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Derive a neutral for grounding purposes.
The capacitors should be discharged.
200 volts AC.

27. 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?
800 volts.
Reverse any two-phase leads.
Two speeds
Clamp-on ammeter.

28. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
200 volts AC.
A device used to store electrical energy.
Isolation transformer.
They should be made by the same manufacturer.

29. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
The current will read zero.
Hyperventilation.
7 -630 volts.
Squirrel-cage induction motor.

30. The speed of an alternating current - squirrel-cage induction motor is...
Continuous.
Squirrel-cage rotor.
A step-up transformer.
Nearly constant.

31. Not a symptom of electrical shock?.
Hyperventilation.
Shunted and taped
5:1.
Inductance.

32. 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?
200 volts AC.
The capacitors should be discharged.
Second-degree burn.
75 turns.

33. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Zero amps.
Circuit Breaker.
75 turns.
A grounding resistor.

34. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Nearly constant.
They must be installed at least 7 feet above the ground.
480 volts.
Reverse any two-phase leads.

35. 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...
Tied together
800 volts.
Inductance.
Capacitance.

36. What type motor is a wound-rotor induction motor?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Squirrel-cage rotor.
A.C.
Inductance.

37. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
15 feet off the ground.
Alternating current.
A device used to store electrical energy.

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

39. If any two-phase wires are reversed on a three-phase motor - the motor will...
5:1.
Reverse its rotation.
600 volts.
Squirrel-cage induction motor.

40. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
1 amp.
Full-load - three-phase voltage.
277 volts.
Four times less than that of the secondary.

41. High voltage is used to transmit power over long distances...
75 turns.
Derive a neutral for grounding purposes.
Because less current flowing at high voltage causes less line loss per kilowatt.
60 Hertz

42. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
An electromagnet.
The chest should rise or inflate.
800 volts.
1 amp.

43. 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.
They must be installed at least 7 feet above the ground.
150 turns.
Grounded phase and ground fault devices were not operating.

44. The standard frequency of alternating current used at a mine is...
A grounding resistor.
60 Hertz
Four times less than that of the secondary.
Provides single-phase power to smaller loads such as lights - heaters - etc.

45. Not true about AC power?
277 volts.
It provides good speed control.
Check to make sure that the victim is not still in contact with the electricity.
Transformer

46. The transformer used only to measure voltage is a...
25 feet.
150 turns.
Potential transformer.
75 turns.

47. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Lower current and higher voltage.
They should be made by the same manufacturer.
The motor rotation is reversed.

48. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Full-load - three-phase voltage.
Tied together
Reverse any two-phase leads.
Short-circuited after power has been removed.

49. 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...
At least two phases
100 volts.
They should be made by the same manufacturer.
Two speeds

50. Where should grounding resistors be located?
Second-degree burn.
Continuous.
At the source transformer.
2000 watts