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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 burn causing a blister is classified as a...
Tied together
Second-degree burn.
At least two phases
Draw less current.

2. A solenoid coil is...
They must be installed at least 7 feet above the ground.
Nearly constant.
Draw less current.
An electromagnet.

3. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
5:1
Two speeds
Transformer

4. All transformers step voltage up or down by...
Inductance.
Cut around clothing that has adhered to the burned area.
2000 watts
Current changing constantly in magnitude and periodically in direction.

5. A wound-rotor induction motor has all the following EXCEPT...
Clamp-on ammeter.
75 turns.
Squirrel-cage rotor.
Kilovolt ampere (KVA).

6. The property of an electric circuit that opposes any change in current is called...
Inductance.
Disconnect the frame-grounding conductor.
Hyperventilation.
60 Hertz

7. Three-phase AC underground cables must be provided with overcurrent protection using a...
800 volts.
Circuit Breaker.
Four times less than that of the secondary.
Provides single-phase power to smaller loads such as lights - heaters - etc.

8. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
60 Hertz
480 volts.
5:1

9. High voltage is used to transmit power over long distances...
Stator windings.
Because less current flowing at high voltage causes less line loss per kilowatt.
A device used to store electrical energy.
The motor rotation is reversed.

10. 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?
100 turns.
Isolation transformer.
12 to 15 times a minute.
The capacitors should be discharged.

11. Compared to the secondary of a loaded - step-down transformer - the primary has...
They must be installed at least 7 feet above the ground.
An electromagnet.
It provides good speed control.
Lower current and higher voltage

12. 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?
600 volts.
150 turns.
A.C.
100 turns.

13. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Draw less current.
Grounded phase and ground fault devices were not operating.
Larger than that found in the primary winding.
12 to 15 times a minute.

14. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Capacitance.
Stator windings.
277 volts.
Two speeds

15. What is a capacitor?
Provides single-phase power to smaller loads such as lights - heaters - etc.
A device used to store electrical energy.
60 cycles per second (60 Hertz).
Hyperventilation.

16. What should the duty rating of a grounding resistor be?
At the source transformer.
Carotid pulse - which is located in the neck next to the Adam's apple.
Continuous.
Alternating current.

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...
It provides good speed control.
Cut around clothing that has adhered to the burned area.
3 -979 Volts.
Draw less current.

18. The main function of CT's and PT's on a main substation is to...
H terminals.
Squirrel-cage rotor.
Allow for metering voltage and Current.
1 amp.

19. Where should grounding resistors be located?
Potential transformer.
Lower current and higher voltage.
Allow for metering voltage and Current.
At the source transformer.

20. A control power transformer...
1 amp.
Shunted and taped
No.6 AWG.
Provides single-phase power to smaller loads such as lights - heaters - etc.

21. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Full-load - three-phase voltage.
Disconnect the frame-grounding conductor.
Shunted and taped
Short-circuited after power has been removed.

22. 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?
800 volts.
75 turns.
12 to 15 times a minute.
200 volts AC.

23. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
At least two phases
Draw less current.
Electro-magnetism for their operation.
They should be made by the same manufacturer.

24. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
A grounding resistor.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Squirrel-cage induction motor.
The motor rotation is reversed.

25. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
2000 watts
The sum of the two capacitors.
Capacitance.
The capacitors should be discharged.

26. 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?
25 feet.
75 turns.
Reverse any two-phase leads.
Cut around clothing that has adhered to the burned area.

27. 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?
An electrical shock hazard may exist.
200 volts AC.
X.
5:1

28. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Capacitance.
25 feet.
Derive a neutral for grounding purposes.
5:1.

29. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Nearly constant.
Zero amps.
1 amp.
At least two phases

30. The standard frequency of alternating current used at a mine is...
60 Hertz
Kilovolt ampere (KVA).
Zero amps.
Isolation transformer.

31. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
3 -979 Volts.
Current changing constantly in magnitude and periodically in direction.
Second-degree burn.

32. What is the first step to be followed in aiding a victim of electrical shock?
7 -630 volts.
Nearly constant.
Draw less current.
Check to make sure that the victim is not still in contact with the electricity.

33. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Lower current and higher voltage.
1 amp.
12 to 15 times a minute.

34. The speed of an alternating current - squirrel-cage induction motor is...
Two speeds
Squirrel-cage induction motor.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Nearly constant.

35. Which of the following does a squirrel cage induction motor have?
Full-load - three-phase voltage.
Capacitance.
At least two phases
Stator windings.

36. Not a symptom of electrical shock?.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
A grounding resistor.
Hyperventilation.
The chest should rise or inflate.

37. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
A device used to store electrical energy.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
H terminals.

38. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Disconnect the frame-grounding conductor.
75 turns.
15 feet off the ground.
277 volts.

39. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Alternating current.
Reverse any two-phase leads.
They must be installed at least 7 feet above the ground.

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...
At least two phases
Clamp-on ammeter.
Tied together
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

41. The size of a transformer is measured in...
3 -979 Volts.
5:1.
200 volts AC.
Kilovolt ampere (KVA).

42. Operating coils - motors - transformers - relays and solenoids depend upon...
Allow for metering voltage and Current.
Draw less current.
Electro-magnetism for their operation.
No.6 AWG.

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...
Lower current and higher voltage.
Draw less current.
Nearly constant.
800 volts.

44. 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?
A.C.
600 volts.
277 volts.
100 turns.

45. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
800 volts.
60 Hertz
100 turns.
X.

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

47. Compared to the secondary of a loaded - step-down transformer - the primary has...
Hyperventilation.
5:1
Lower current and higher voltage.
75 turns.

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

49. Not true about AC power?
Larger than that found in the primary winding.
It provides good speed control.
Squirrel-cage induction motor.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

50. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Two speeds
Four times less than that of the secondary.
Shunted and taped
Squirrel-cage rotor.