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 secondary windings on a 10:1 step-down transformer will have a wire size...
Because less current flowing at high voltage causes less line loss per kilowatt.
Larger than that found in the primary winding.
100 turns.
A.C.


2. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Inductance.
Nearly constant.
Stator windings.


3. 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
Potential transformer.
Full-load - three-phase voltage.
The sum of the two capacitors.


4. 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?
Because less current flowing at high voltage causes less line loss per kilowatt.
It provides good speed control.
Electro-magnetism for their operation.
75 turns.


5. When not connected to a load - the secondary leads of a current transformer should be...
It provides good speed control.
Shunted and taped
800 volts.
Tied together


6. What steps up or steps down AC voltage?
No.6 AWG.
Transformer
60 cycles per second (60 Hertz).
Lower current and higher voltage.


7. The transformer used only to measure voltage is a...
2000 watts
Carotid pulse - which is located in the neck next to the Adam's apple.
5:1
Potential transformer.


8. The property of an electrical circuit that opposes any change in voltage is called...
100 volts.
They should be made by the same manufacturer.
Derive a neutral for grounding purposes.
Capacitance.


9. Three-phase AC underground cables must be provided with overcurrent protection using a...
Disconnect the frame-grounding conductor.
An electrical shock hazard may exist.
75 turns.
Circuit Breaker.


10. 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.
60 cycles per second (60 Hertz).
60 Hertz
5:1.
Hyperventilation.


11. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Transformer
No.6 AWG.
277 volts.
60 cycles per second (60 Hertz).


12. What should the duty rating of a grounding resistor be?
Draw less current.
Inductance.
Continuous.
Check to make sure that the victim is not still in contact with the electricity.


13. Current that changes periodically in direction is...
Continuous.
277 volts.
A device used to store electrical energy.
Alternating current.


14. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
100 volts.
12 to 15 times a minute.
Current that changes constantly in magnitude and periodically in direction.


15. Which of the following does a squirrel cage induction motor have?
12 to 15 times a minute.
A step-up transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Stator windings.


16. What type motor is a wound-rotor induction motor?
They must be installed at least 7 feet above the ground.
1 amp.
A.C.
Isolation transformer.


17. High voltage is used to transmit power over long distances...
Transformers.
Squirrel-cage rotor.
Short-circuited after power has been removed.
Because less current flowing at high voltage causes less line loss per kilowatt.


18. How do you change the direction of a 3-phase AC motor?
At least two phases
Reverse any two-phase leads.
An electromagnet.
Kilovolt ampere (KVA).


19. AC voltage is raised or lowered by means of...
Current changing constantly in magnitude and periodically in direction.
Check to make sure that the victim is not still in contact with the electricity.
Transformers.
Clamp-on ammeter.


20. Not true about AC power?
No.6 AWG.
Disconnect the frame-grounding conductor.
H terminals.
It provides good speed control.


21. At what rate should mouth-to-mouth resuscitation be applied?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The current will read zero.
200 volts AC.
12 to 15 times a minute.


22. The size of a transformer is measured in...
Larger than that found in the primary winding.
The motor rotation is reversed.
60 Hertz
Kilovolt ampere (KVA).


23. 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?
800 volts.
Squirrel-cage rotor.
100 turns.
100 volts.


24. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Potential transformer.
15 feet off the ground.
At the source transformer.
The chest should rise or inflate.


25. Where should grounding resistors be located?
At the source transformer.
2000 watts
Reverse its rotation.
Two speeds


26. A transformer with a 1:1 ratio is usually a (an)...
7 -630 volts.
Lower current and higher voltage
Isolation transformer.
The chest should rise or inflate.


27. 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?
It provides good speed control.
H terminals.
75 turns.
Isolation transformer.


28. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
5:1.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
15 feet off the ground.
75 turns.


29. A wound-rotor induction motor has all the following EXCEPT...
Inductance.
Squirrel-cage rotor.
Isolation transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.


30. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Capacitance.
100 volts.
A step-up transformer.


31. The property of an electric circuit that opposes any change in current is called...
15 feet off the ground.
Inductance.
Hyperventilation.
3 -979 Volts.


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


33. 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...
Shunted and taped
Tied together
Reverse any two-phase leads.
Lower current and higher voltage.


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?
Check to make sure that the victim is not still in contact with the electricity.
Tied together
800 volts.
Continuous.


35. Not a symptom of electrical shock?.
25 feet.
Hyperventilation.
Cut around clothing that has adhered to the burned area.
The chest should rise or inflate.


36. 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...
800 volts.
Draw less current.
At the source transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.


37. The speed of an alternating current - squirrel-cage induction motor is...
Allow for metering voltage and Current.
Nearly constant.
Current that changes constantly in magnitude and periodically in direction.
Second-degree burn.


38. The standard frequency of power supplied by the power company is...
Check to make sure that the victim is not still in contact with the electricity.
100 volts.
Inductance.
60 cycles per second (60 Hertz).


39. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Isolation transformer.
Grounded phase and ground fault devices were not operating.
Transformer
1 amp.


40. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Current that changes constantly in magnitude and periodically in direction.
H terminals.
The capacitors should be discharged.
They must be installed at least 7 feet above the ground.


41. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
The sum of the two capacitors.
60 cycles per second (60 Hertz).
200 volts AC.
25 feet.


42. Compared to the secondary of a loaded - step-down transformer - the primary has...
Inductance.
Grounded phase and ground fault devices were not operating.
Lower current and higher voltage.
200 volts AC.


43. What is a capacitor?
Allow for metering voltage and Current.
Provides single-phase power to smaller loads such as lights - heaters - etc.
A.C.
A device used to store electrical energy.


44. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Full-load - three-phase voltage.
They must be installed at least 7 feet above the ground.
A step-up transformer.
Circuit Breaker.


45. 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?
Allow for metering voltage and Current.
The current will read zero.
60 Hertz
150 turns.


46. Current transformers - or CT's - are used to...
They should be made by the same manufacturer.
Disconnect the frame-grounding conductor.
Capacitance.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.


47. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Squirrel-cage induction motor.
150 turns.
Four times less than that of the secondary.
Transformer


48. Compared to the secondary of a loaded - step-down transformer - the primary has...
The chest should rise or inflate.
The sum of the two capacitors.
It provides good speed control.
Lower current and higher voltage


49. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
They must be installed at least 7 feet above the ground.
Isolation transformer.
Larger than that found in the primary winding.
Two speeds


50. What type of 3-phase AC motor is used most often around a mine?
Kilovolt ampere (KVA).
Squirrel-cage induction motor.
Zero amps.
Derive a neutral for grounding purposes.