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. At what rate should mouth-to-mouth resuscitation be applied?
Nearly constant.
25 feet.
12 to 15 times a minute.
Kilovolt ampere (KVA).


2. If any two-phase wires are reversed on a three-phase motor - the motor will...
Isolation transformer.
Reverse its rotation.
They must be installed at least 7 feet above the ground.
5:1.


3. High voltage is used to transmit power over long distances...
The sum of the two capacitors.
Because less current flowing at high voltage causes less line loss per kilowatt.
Clamp-on ammeter.
800 volts.


4. Current transformers - or CT's - are used to...
Circuit Breaker.
It provides good speed control.
At least two phases
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.


5. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
100 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
5:1.


6. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
60 cycles per second (60 Hertz).
They should be made by the same manufacturer.
7 -630 volts.
Cut around clothing that has adhered to the burned area.


7. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
The sum of the two capacitors.
A grounding resistor.
At the source transformer.


8. 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?
The chest should rise or inflate.
150 turns.
The motor rotation is reversed.
Continuous.


9. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
At the source transformer.
Second-degree burn.
Because less current flowing at high voltage causes less line loss per kilowatt.
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?
Reverse its rotation.
Transformers.
100 turns.
Alternating current.


11. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
They should be made by the same manufacturer.
Current changing constantly in magnitude and periodically in direction.
Electro-magnetism for their operation.


12. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
An electromagnet.
7 -630 volts.
Tied together
The sum of the two capacitors.


13. Compared to the secondary of a loaded - step-down transformer - the primary has...
480 volts.
Potential transformer.
The chest should rise or inflate.
Lower current and higher voltage.


14. Not a symptom of electrical shock?.
Hyperventilation.
15 feet off the ground.
Four times less than that of the secondary.
Lower current and higher voltage.


15. What type of 3-phase AC motor is used most often around a mine?
75 turns.
Draw less current.
No.6 AWG.
Squirrel-cage induction motor.


16. The size of a transformer is measured in...
60 cycles per second (60 Hertz).
Lower current and higher voltage.
Kilovolt ampere (KVA).
Nearly constant.


17. 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.
Draw less current.
At the source transformer.
25 feet.


18. What is the danger when working around capacitors?
Current that changes constantly in magnitude and periodically in direction.
At least two phases
An electrical shock hazard may exist.
The sum of the two capacitors.


19. The main function of CT's and PT's on a main substation is to...
Grounded phase and ground fault devices were not operating.
Current changing constantly in magnitude and periodically in direction.
Allow for metering voltage and Current.
100 volts.


20. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
An electromagnet.
Grounded phase and ground fault devices were not operating.
A grounding resistor.
12 to 15 times a minute.


21. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
7 -630 volts.
Transformers.
277 volts.
At the source transformer.


22. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
The capacitors should be discharged.
X.
H terminals.
Nearly constant.


23. 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.
They should be made by the same manufacturer.
Lower current and higher voltage.
Allow for metering voltage and Current.


24. What type motor is a wound-rotor induction motor?
Disconnect the frame-grounding conductor.
A.C.
Short-circuited after power has been removed.
Circuit Breaker.


25. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
They must be installed at least 7 feet above the ground.
Carotid pulse - which is located in the neck next to the Adam's apple.
15 feet off the ground.


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?
The sum of the two capacitors.
Transformer
75 turns.
150 turns.


27. 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
It provides good speed control.
Electro-magnetism for their operation.
Reverse any two-phase leads.


28. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Clamp-on ammeter.
100 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.


29. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
12 to 15 times a minute.
X.
200 volts AC.


30. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
5:1.
The motor rotation is reversed.
100 turns.
15 feet off the ground.


31. How should clothing be removed from a burn?
75 turns.
Circuit Breaker.
Cut around clothing that has adhered to the burned area.
Provides single-phase power to smaller loads such as lights - heaters - etc.


32. The standard frequency of alternating current used at a mine is...
The current will read zero.
A.C.
60 Hertz
Current that changes constantly in magnitude and periodically in direction.


33. A solenoid coil is...
Hyperventilation.
An electromagnet.
2000 watts
Alternating current.


34. 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?
Because less current flowing at high voltage causes less line loss per kilowatt.
800 volts.
Continuous.
Reverse any two-phase leads.


35. When not connected to a load - the secondary leads of a current transformer should be...
Four times less than that of the secondary.
The sum of the two capacitors.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Shunted and taped


36. What should the duty rating of a grounding resistor be?
H terminals.
Continuous.
3 -979 Volts.
Allow for metering voltage and Current.


37. What is a capacitor?
A device used to store electrical energy.
Derive a neutral for grounding purposes.
It provides good speed control.
75 turns.


38. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
25 feet.
600 volts.
It provides good speed control.


39. 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?
Reverse any two-phase leads.
600 volts.
Allow for metering voltage and Current.
15 feet off the ground.


40. 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.
A device used to store electrical energy.
Stator windings.
Lower current and higher voltage.


41. The speed of an alternating current - squirrel-cage induction motor is...
Lower current and higher voltage.
Shunted and taped
25 feet.
Nearly constant.


42. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
Draw less current.
5:1
12 to 15 times a minute.


43. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Draw less current.
No.6 AWG.
Lower current and higher voltage.
Clamp-on ammeter.


44. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Full-load - three-phase voltage.
Allow for metering voltage and Current.
1 amp.
Kilovolt ampere (KVA).


45. Current that changes periodically in direction is...
Alternating current.
They must be installed at least 7 feet above the ground.
Tied together
Provides single-phase power to smaller loads such as lights - heaters - etc.


46. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Second-degree burn.
Nearly constant.
The chest should rise or inflate.
2000 watts


47. Three-phase AC underground cables must be provided with overcurrent protection using a...
Transformers.
Current changing constantly in magnitude and periodically in direction.
Circuit Breaker.
Grounded phase and ground fault devices were not operating.


48. Not an acceptable method for the installations of surface transformers?
Larger than that found in the primary winding.
They must be installed at least 7 feet above the ground.
2000 watts
Clamp-on ammeter.


49. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Hyperventilation.
At least two phases
Check to make sure that the victim is not still in contact with the electricity.
Continuous.


50. 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...
A device used to store electrical energy.
No.6 AWG.
Second-degree burn.
Draw less current.