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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. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Reverse any two-phase leads.
5:1.
Two speeds
Capacitance.

2. Operating coils - motors - transformers - relays and solenoids depend upon...
600 volts.
Transformers.
A device used to store electrical energy.
Electro-magnetism for their operation.

3. The size of a transformer is measured in...
Kilovolt ampere (KVA).
They must be installed at least 7 feet above the ground.
Lower current and higher voltage.
Squirrel-cage induction motor.

4. The primary function of a power transformer is to provide...
Larger than that found in the primary winding.
Tied together
A device used to store electrical energy.
Full-load - three-phase voltage.

5. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Continuous.
X.
7 -630 volts.
The sum of the two capacitors.

6. A burn causing a blister is classified as a...
Second-degree burn.
Four times less than that of the secondary.
The sum of the two capacitors.
Disconnect the frame-grounding conductor.

7. 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.
480 volts.
H terminals.
Lower current and higher voltage

8. 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.
Transformers.
The capacitors should be discharged.
The motor rotation is reversed.

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
Capacitance.
A step-up transformer.
Full-load - three-phase voltage.

10. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
Current that changes constantly in magnitude and periodically in direction.
75 turns.
200 volts AC.

11. The standard frequency of power supplied by the power company is...
Reverse any two-phase leads.
Squirrel-cage rotor.
60 cycles per second (60 Hertz).
The chest should rise or inflate.

12. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Clamp-on ammeter.
The current will read zero.

13. 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.
150 turns.
Circuit Breaker.

14. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Reverse its rotation.
Hyperventilation.
No.6 AWG.
Four times less than that of the secondary.

15. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Kilovolt ampere (KVA).
Squirrel-cage induction motor.
Tied together
A step-up transformer.

16. What is the first step to be followed in aiding a victim of electrical shock?
Lower current and higher voltage
They must be installed at least 7 feet above the ground.
Check to make sure that the victim is not still in contact with the electricity.
Reverse its rotation.

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

18. 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
Carotid pulse - which is located in the neck next to the Adam's apple.
800 volts.
60 Hertz

19. Not an acceptable method for the installations of surface transformers?
480 volts.
Clamp-on ammeter.
The sum of the two capacitors.
They must be installed at least 7 feet above the ground.

20. Current that changes periodically in direction is...
Alternating current.
Transformers.
Check to make sure that the victim is not still in contact with the electricity.
Draw less current.

21. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
150 turns.
Check to make sure that the victim is not still in contact with the electricity.
Stator windings.

22. 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...
Hyperventilation.
Draw less current.
12 to 15 times a minute.
Squirrel-cage induction motor.

23. What is a capacitor?
7 -630 volts.
Larger than that found in the primary winding.
Tied together
A device used to store electrical energy.

24. Not true about AC power?
3 -979 Volts.
Allow for metering voltage and Current.
It provides good speed control.
Draw less current.

25. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
Squirrel-cage induction motor.
Derive a neutral for grounding purposes.
5:1.

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?
1 amp.
An electromagnet.
Squirrel-cage induction motor.
75 turns.

27. 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...
Continuous.
200 volts AC.
7 -630 volts.
100 volts.

28. Define alternating current...
Alternating current.
150 turns.
Lower current and higher voltage
Current changing constantly in magnitude and periodically in direction.

29. 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?
480 volts.
150 turns.
Isolation transformer.
2000 watts

30. What is the danger when working around capacitors?
At least two phases
Cut around clothing that has adhered to the burned area.
An electrical shock hazard may exist.
Alternating current.

31. 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
60 Hertz
100 turns.
Inductance.

32. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Hyperventilation.
At least two phases
3 -979 Volts.
They must be installed at least 7 feet above the ground.

33. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A grounding resistor.
100 turns.
277 volts.
X.

34. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Two speeds
7 -630 volts.
Hyperventilation.
1 amp.

35. The combined capacitance of two capacitors in parallel is...
75 turns.
The sum of the two capacitors.
Current that changes constantly in magnitude and periodically in direction.
Larger than that found in the primary winding.

36. Not a symptom of electrical shock?.
Clamp-on ammeter.
Lower current and higher voltage.
Hyperventilation.
Squirrel-cage rotor.

37. The speed of an alternating current - squirrel-cage induction motor is...
Grounded phase and ground fault devices were not operating.
Nearly constant.
Squirrel-cage rotor.
1 amp.

38. 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.
No.6 AWG.
Clamp-on ammeter.
A step-up transformer.

39. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Carotid pulse - which is located in the neck next to the Adam's apple.
An electrical shock hazard may exist.
Because less current flowing at high voltage causes less line loss per kilowatt.
2000 watts

40. The purpose of a zig-zag transformer is to...
75 turns.
Derive a neutral for grounding purposes.
Shunted and taped
277 volts.

41. What steps up or steps down AC voltage?
150 turns.
Draw less current.
Because less current flowing at high voltage causes less line loss per kilowatt.
Transformer

42. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
No.6 AWG.
The chest should rise or inflate.
The capacitors should be discharged.
Grounded phase and ground fault devices were not operating.

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...
Reverse its rotation.
Draw less current.
Derive a neutral for grounding purposes.
X.

44. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
277 volts.
A device used to store electrical energy.
75 turns.
7 -630 volts.

45. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Inductance.
No.6 AWG.
7 -630 volts.

46. When not connected to a load - the secondary leads of a current transformer should be...
Circuit Breaker.
Shunted and taped
Draw less current.
Isolation transformer.

47. The secondary windings on a 10:1 step-down transformer will have a wire size...
Kilovolt ampere (KVA).
Shunted and taped
Larger than that found in the primary winding.
Carotid pulse - which is located in the neck next to the Adam's apple.

48. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Because less current flowing at high voltage causes less line loss per kilowatt.
At the source transformer.
Grounded phase and ground fault devices were not operating.
A grounding resistor.

49. Where should grounding resistors be located?
A device used to store electrical energy.
60 Hertz
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
At the source transformer.

50. A solenoid coil is...
An electromagnet.
Hyperventilation.
15 feet off the ground.
The chest should rise or inflate.