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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. Compared to the secondary of a loaded - step-down transformer - the primary has...
100 turns.
Kilovolt ampere (KVA).
The current will read zero.
Lower current and higher voltage.

2. The size of a transformer is measured in...
Current that changes constantly in magnitude and periodically in direction.
Kilovolt ampere (KVA).
Shunted and taped
Cut around clothing that has adhered to the burned area.

3. What type of 3-phase AC motor is used most often around a mine?
Check to make sure that the victim is not still in contact with the electricity.
Squirrel-cage induction motor.
100 volts.
480 volts.

4. What type motor is a wound-rotor induction motor?
A grounding resistor.
A.C.
The motor rotation is reversed.
An electrical shock hazard may exist.

5. A solenoid coil is...
A device used to store electrical energy.
Allow for metering voltage and Current.
An electromagnet.
Full-load - three-phase voltage.

6. Alternating current may be defined as...
75 turns.
480 volts.
Current that changes constantly in magnitude and periodically in direction.
Squirrel-cage induction motor.

7. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
The motor rotation is reversed.
3 -979 Volts.
Short-circuited after power has been removed.

8. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
Isolation transformer.
Clamp-on ammeter.
25 feet.

9. What steps up or steps down AC voltage?
Isolation transformer.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Transformer
At the source transformer.

10. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
At least two phases
Lower current and higher voltage
A.C.

11. The transformer used only to measure voltage is a...
5:1.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Potential transformer.
60 cycles per second (60 Hertz).

12. 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?
3 -979 Volts.
Transformers.
Hyperventilation.
Provides single-phase power to smaller loads such as lights - heaters - etc.

13. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Isolation transformer.
Clamp-on ammeter.
15 feet off the ground.
Larger than that found in the primary winding.

14. If any two-phase wires are reversed on a three-phase motor - the motor will...
Zero amps.
Alternating current.
Cut around clothing that has adhered to the burned area.
Reverse its rotation.

15. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
It provides good speed control.
A grounding resistor.
75 turns.

16. The purpose of a zig-zag transformer is to...
Because less current flowing at high voltage causes less line loss per kilowatt.
Isolation transformer.
Disconnect the frame-grounding conductor.
Derive a neutral for grounding purposes.

17. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Because less current flowing at high voltage causes less line loss per kilowatt.
Transformers.
A device used to store electrical energy.

18. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
X.
1 amp.
Transformers.
100 volts.

19. 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?
200 volts AC.
Derive a neutral for grounding purposes.
A device used to store electrical energy.
15 feet off the ground.

20. 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...
800 volts.
Tied together
X.
Squirrel-cage induction motor.

21. Not a symptom of electrical shock?.
Stator windings.
A device used to store electrical energy.
Hyperventilation.
150 turns.

22. The speed of an alternating current - squirrel-cage induction motor is...
Allow for metering voltage and Current.
480 volts.
Nearly constant.
Draw less current.

23. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
800 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Larger than that found in the primary winding.
100 turns.

24. The primary leads of a single-phase transformer should be connected to the...
H terminals.
Larger than that found in the primary winding.
Cut around clothing that has adhered to the burned area.
Squirrel-cage rotor.

25. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Inductance.
Short-circuited after power has been removed.
It provides good speed control.
Lower current and higher voltage

26. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
An electromagnet.
No.6 AWG.
Carotid pulse - which is located in the neck next to the Adam's apple.
277 volts.

27. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Kilovolt ampere (KVA).
The capacitors should be discharged.
Larger than that found in the primary winding.
The sum of the two capacitors.

28. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Circuit Breaker.
Four times less than that of the secondary.
Disconnect the frame-grounding conductor.
The chest should rise or inflate.

29. A transformer with a 1:1 ratio is usually a (an)...
Lower current and higher voltage.
Isolation transformer.
X.
The current will read zero.

30. High voltage is used to transmit power over long distances...
Reverse its rotation.
Current that changes constantly in magnitude and periodically in direction.
Because less current flowing at high voltage causes less line loss per kilowatt.
The motor rotation is reversed.

31. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
X.
5:1
They must be installed at least 7 feet above the ground.
They should be made by the same manufacturer.

32. Which of the following does a squirrel cage induction motor have?
The capacitors should be discharged.
Stator windings.
A grounding resistor.
75 turns.

33. The primary function of a power transformer is to provide...
Squirrel-cage induction motor.
Current that changes constantly in magnitude and periodically in direction.
At least two phases
Full-load - three-phase voltage.

34. 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.
Inductance.
It provides good speed control.
Two speeds

35. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Carotid pulse - which is located in the neck next to the Adam's apple.
Draw less current.
Current that changes constantly in magnitude and periodically in direction.

36. What is a capacitor?
A.C.
A device used to store electrical energy.
Stator windings.
Reverse any two-phase leads.

37. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Four times less than that of the secondary.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
A.C.
Potential transformer.

38. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
No.6 AWG.
They must be installed at least 7 feet above the ground.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
X.

39. A control power transformer...
Carotid pulse - which is located in the neck next to the Adam's apple.
Larger than that found in the primary winding.
Provides single-phase power to smaller loads such as lights - heaters - etc.
7 -630 volts.

40. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
The motor rotation is reversed.
The current will read zero.
Four times less than that of the secondary.

41. Current that changes periodically in direction is...
Clamp-on ammeter.
Alternating current.
Derive a neutral for grounding purposes.
H terminals.

42. 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?
150 turns.
Capacitance.
A grounding resistor.
Current that changes constantly in magnitude and periodically in direction.

43. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Provides single-phase power to smaller loads such as lights - heaters - etc.
3 -979 Volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
The current will read zero.

44. What is the danger when working around capacitors?
Four times less than that of the secondary.
Reverse any two-phase leads.
An electrical shock hazard may exist.
No.6 AWG.

45. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
480 volts.
Grounded phase and ground fault devices were not operating.
Draw less current.
Short-circuited after power has been removed.

46. 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.
A grounding resistor.
5:1
An electrical shock hazard may exist.
Squirrel-cage induction motor.

47. 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?
Capacitance.
An electrical shock hazard may exist.
75 turns.
60 Hertz

48. 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...
Transformers.
The capacitors should be discharged.
They must be installed at least 7 feet above the ground.
Draw less current.

49. Operating coils - motors - transformers - relays and solenoids depend upon...
Short-circuited after power has been removed.
Hyperventilation.
Circuit Breaker.
Electro-magnetism for their operation.

50. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
The sum of the two capacitors.
Full-load - three-phase voltage.
Draw less current.
Disconnect the frame-grounding conductor.