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...
150 turns.
Lower current and higher voltage
Derive a neutral for grounding purposes.
The capacitors should be discharged.


2. What is a capacitor?
Reverse its rotation.
A device used to store electrical energy.
Lower current and higher voltage
150 turns.


3. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
Derive a neutral for grounding purposes.
Draw less current.
100 turns.


4. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The sum of the two capacitors.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Draw less current.
The motor rotation is reversed.


5. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
200 volts AC.
Draw less current.
Four times less than that of the secondary.
The capacitors should be discharged.


6. Current in an AC circuit may be measured by...
They must be installed at least 7 feet above the ground.
Clamp-on ammeter.
Reverse its rotation.
150 turns.


7. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
480 volts.
Stator windings.
Inductance.


8. The secondary windings on a 10:1 step-down transformer will have a wire size...
The chest should rise or inflate.
Short-circuited after power has been removed.
Capacitance.
Larger than that found in the primary winding.


9. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Clamp-on ammeter.
Lower current and higher voltage.
Squirrel-cage induction motor.


10. What steps up or steps down AC voltage?
5:1
Transformer
Inductance.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.


11. 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.
A.C.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Two speeds


12. 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?
Draw less current.
Hyperventilation.
800 volts.
Continuous.


13. Not an acceptable method for the installations of surface transformers?
Draw less current.
They must be installed at least 7 feet above the ground.
1 amp.
Alternating current.


14. Define alternating current...
Draw less current.
Current changing constantly in magnitude and periodically in direction.
100 volts.
3 -979 Volts.


15. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
Inductance.
5:1.
60 Hertz


16. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
60 cycles per second (60 Hertz).
An electromagnet.
277 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.


17. The property of an electrical circuit that opposes any change in voltage is called...
100 turns.
A.C.
They must be installed at least 7 feet above the ground.
Capacitance.


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


19. 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.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The current will read zero.
Potential transformer.


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...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Tied together
200 volts AC.
60 Hertz


21. Which of the following does a squirrel cage induction motor have?
Stator windings.
75 turns.
5:1
Second-degree burn.


22. A solenoid coil is...
X.
277 volts.
480 volts.
An electromagnet.


23. Where should grounding resistors be located?
At the source transformer.
5:1
Transformer
75 turns.


24. 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?
A grounding resistor.
Current that changes constantly in magnitude and periodically in direction.
75 turns.
7 -630 volts.


25. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Current that changes constantly in magnitude and periodically in direction.
Tied together
Transformers.


26. Not a symptom of electrical shock?.
Inductance.
Kilovolt ampere (KVA).
Hyperventilation.
The motor rotation is reversed.


27. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
480 volts.
Isolation transformer.
No.6 AWG.
Disconnect the frame-grounding conductor.


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


29. 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.
15 feet off the ground.
5:1.
H terminals.
1 amp.


30. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Disconnect the frame-grounding conductor.
Reverse its rotation.
150 turns.
2000 watts


31. A control power transformer...
800 volts.
Clamp-on ammeter.
They should be made by the same manufacturer.
Provides single-phase power to smaller loads such as lights - heaters - etc.


32. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
60 Hertz
480 volts.
The chest should rise or inflate.
A grounding resistor.


33. The purpose of a zig-zag transformer is to...
At least two phases
Larger than that found in the primary winding.
Derive a neutral for grounding purposes.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.


34. All transformers step voltage up or down by...
7 -630 volts.
25 feet.
Alternating current.
Inductance.


35. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
60 cycles per second (60 Hertz).
Hyperventilation.
Full-load - three-phase voltage.
Short-circuited after power has been removed.


36. 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
60 cycles per second (60 Hertz).
Hyperventilation.
Grounded phase and ground fault devices were not operating.


37. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
200 volts AC.
100 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
60 cycles per second (60 Hertz).


38. The primary leads of a single-phase transformer should be connected to the...
800 volts.
H terminals.
The sum of the two capacitors.
Nearly constant.


39. The size of a transformer is measured in...
A grounding resistor.
5:1.
Kilovolt ampere (KVA).
Electro-magnetism for their operation.


40. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Transformers.
Transformer
They should be made by the same manufacturer.
X.


41. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
H terminals.
150 turns.
The current will read zero.
X.


42. A wound-rotor induction motor has all the following EXCEPT...
The motor rotation is reversed.
15 feet off the ground.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Squirrel-cage rotor.


43. A burn causing a blister is classified as a...
Second-degree burn.
7 -630 volts.
Kilovolt ampere (KVA).
Continuous.


44. If any two-phase wires are reversed on a three-phase motor - the motor will...
Inductance.
Full-load - three-phase voltage.
Short-circuited after power has been removed.
Reverse its rotation.


45. A transformer with a 1:1 ratio is usually a (an)...
Reverse any two-phase leads.
Kilovolt ampere (KVA).
Isolation transformer.
H terminals.


46. What is the danger when working around capacitors?
Electro-magnetism for their operation.
Circuit Breaker.
Current that changes constantly in magnitude and periodically in direction.
An electrical shock hazard may exist.


47. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Lower current and higher voltage.
The capacitors should be discharged.
At the source transformer.
A.C.


48. When not connected to a load - the secondary leads of a current transformer should be...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
No.6 AWG.
Shunted and taped
An electromagnet.


49. 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...
Potential transformer.
Four times less than that of the secondary.
Current changing constantly in magnitude and periodically in direction.
Draw less current.


50. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Shunted and taped
25 feet.
3 -979 Volts.
Clamp-on ammeter.