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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. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Inductance.
H terminals.
Current changing constantly in magnitude and periodically in direction.

2. 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...
At the source transformer.
2000 watts
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Draw less current.

3. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Reverse its rotation.
Two speeds
Nearly constant.
Continuous.

4. High voltage is used to transmit power over long distances...
Inductance.
Hyperventilation.
They should be made by the same manufacturer.
Because less current flowing at high voltage causes less line loss per kilowatt.

5. What is the danger when working around capacitors?
A.C.
Squirrel-cage rotor.
Squirrel-cage induction motor.
An electrical shock hazard may exist.

6. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Electro-magnetism for their operation.
480 volts.
Allow for metering voltage and Current.
Short-circuited after power has been removed.

7. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
Transformers.
Second-degree burn.
Isolation transformer.

8. A burn causing a blister is classified as a...
Derive a neutral for grounding purposes.
600 volts.
Second-degree burn.
H terminals.

9. What should the duty rating of a grounding resistor be?
277 volts.
The sum of the two capacitors.
Continuous.
200 volts AC.

10. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
75 turns.
Isolation transformer.
Inductance.

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

12. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
60 cycles per second (60 Hertz).
A step-up transformer.
The capacitors should be discharged.
Because less current flowing at high voltage causes less line loss per kilowatt.

13. 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.
It provides good speed control.
5:1
Isolation transformer.
1 amp.

14. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
An electromagnet.
It provides good speed control.
Reverse its rotation.
No.6 AWG.

15. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Current that changes constantly in magnitude and periodically in direction.
277 volts.
Disconnect the frame-grounding conductor.
H terminals.

16. 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...
Reverse its rotation.
Kilovolt ampere (KVA).
Tied together
15 feet off the ground.

17. A wound-rotor induction motor has all the following EXCEPT...
Capacitance.
Electro-magnetism for their operation.
Squirrel-cage rotor.
150 turns.

18. The purpose of a zig-zag transformer is to...
Full-load - three-phase voltage.
The capacitors should be discharged.
200 volts AC.
Derive a neutral for grounding purposes.

19. If any two-phase wires are reversed on a three-phase motor - the motor will...
At least two phases
Transformer
Reverse its rotation.
Grounded phase and ground fault devices were not operating.

20. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Four times less than that of the secondary.
They must be installed at least 7 feet above the ground.
The chest should rise or inflate.
The current will read zero.

21. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The current will read zero.
Draw less current.
Electro-magnetism for their operation.
480 volts.

22. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
At least two phases
They should be made by the same manufacturer.
Continuous.

23. Operating coils - motors - transformers - relays and solenoids depend upon...
Isolation transformer.
Cut around clothing that has adhered to the burned area.
At the source transformer.
Electro-magnetism for their operation.

24. Not a symptom of electrical shock?.
They must be installed at least 7 feet above the ground.
Hyperventilation.
Draw less current.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

25. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Inductance.
The capacitors should be discharged.

26. 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...
Electro-magnetism for their operation.
2000 watts
Four times less than that of the secondary.
Draw less current.

27. 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?
100 volts.
The current will read zero.
150 turns.
Current changing constantly in magnitude and periodically in direction.

28. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
The current will read zero.
100 turns.
Full-load - three-phase voltage.

29. What type motor is a wound-rotor induction motor?
15 feet off the ground.
A.C.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
150 turns.

30. What is a capacitor?
A device used to store electrical energy.
Transformers.
75 turns.
The sum of the two capacitors.

31. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Nearly constant.
277 volts.
Cut around clothing that has adhered to the burned area.

32. 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...
2000 watts
Hyperventilation.
Derive a neutral for grounding purposes.
100 volts.

33. A control power transformer...
Derive a neutral for grounding purposes.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Draw less current.
A step-up transformer.

34. Current that changes periodically in direction is...
Larger than that found in the primary winding.
800 volts.
Alternating current.
Two speeds

35. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
3 -979 Volts.
The capacitors should be discharged.
15 feet off the ground.
25 feet.

36. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
100 volts.
They should be made by the same manufacturer.
100 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.

37. What type of 3-phase AC motor is used most often around a mine?
Inductance.
Squirrel-cage induction motor.
A device used to store electrical energy.
200 volts AC.

38. 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?
Cut around clothing that has adhered to the burned area.
The chest should rise or inflate.
600 volts.
Reverse its rotation.

39. The standard frequency of alternating current used at a mine is...
A step-up transformer.
The chest should rise or inflate.
5:1.
60 Hertz

40. 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?
The motor rotation is reversed.
Inductance.
Continuous.
100 turns.

41. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Four times less than that of the secondary.
800 volts.
5:1
Grounded phase and ground fault devices were not operating.

42. Compared to the secondary of a loaded - step-down transformer - the primary has...
2000 watts
Shunted and taped
75 turns.
Lower current and higher voltage

43. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Stator windings.
Inductance.
At least two phases
5:1

44. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Cut around clothing that has adhered to the burned area.
They must be installed at least 7 feet above the ground.
Zero amps.
Transformers.

45. 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?
5:1.
Hyperventilation.
Current that changes constantly in magnitude and periodically in direction.
800 volts.

46. 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?
3 -979 Volts.
A step-up transformer.
75 turns.
Potential transformer.

47. All transformers step voltage up or down by...
Kilovolt ampere (KVA).
Inductance.
Electro-magnetism for their operation.
Clamp-on ammeter.

48. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Hyperventilation.
Short-circuited after power has been removed.
75 turns.

49. Three-phase AC underground cables must be provided with overcurrent protection using a...
25 feet.
Check to make sure that the victim is not still in contact with the electricity.
Circuit Breaker.
Electro-magnetism for their operation.

50. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
60 Hertz
60 cycles per second (60 Hertz).
An electrical shock hazard may exist.