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...
The capacitors should be discharged.
Two speeds
5:1
Alternating current.


2. What is the danger when working around capacitors?
They must be installed at least 7 feet above the ground.
It provides good speed control.
An electrical shock hazard may exist.
Tied together


3. What type motor is a wound-rotor induction motor?
600 volts.
Disconnect the frame-grounding conductor.
A.C.
At the source transformer.


4. The speed of an alternating current - squirrel-cage induction motor is...
Four times less than that of the secondary.
Alternating current.
An electrical shock hazard may exist.
Nearly constant.


5. What is the first step to be followed in aiding a victim of electrical shock?
The current will read zero.
Short-circuited after power has been removed.
Check to make sure that the victim is not still in contact with the electricity.
Larger than that found in the primary winding.


6. 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.
150 turns.
Draw less current.
5:1.
Clamp-on ammeter.


7. The purpose of a zig-zag transformer is to...
The capacitors should be discharged.
At the source transformer.
15 feet off the ground.
Derive a neutral for grounding purposes.


8. When not connected to a load - the secondary leads of a current transformer should be...
Zero amps.
The current will read zero.
Grounded phase and ground fault devices were not operating.
Shunted and taped


9. 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?
Shunted and taped
800 volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
3 -979 Volts.


10. What is a capacitor?
A device used to store electrical energy.
3 -979 Volts.
Larger than that found in the primary winding.
X.


11. 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...
Second-degree burn.
Tied together
The chest should rise or inflate.
Zero amps.


12. 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...
200 volts AC.
Capacitance.
100 turns.
Draw less current.


13. Compared to the secondary of a loaded - step-down transformer - the primary has...
75 turns.
Four times less than that of the secondary.
An electromagnet.
Lower current and higher voltage.


14. 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?
5:1
Reverse any two-phase leads.
Alternating current.
600 volts.


15. High voltage is used to transmit power over long distances...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Because less current flowing at high voltage causes less line loss per kilowatt.
It provides good speed control.
They should be made by the same manufacturer.


16. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Zero amps.
A step-up transformer.
Stator windings.
Current that changes constantly in magnitude and periodically in direction.


17. A wound-rotor induction motor has all the following EXCEPT...
The capacitors should be discharged.
Zero amps.
Squirrel-cage rotor.
Lower current and higher voltage.


18. If any two-phase wires are reversed on a three-phase motor - the motor will...
Circuit Breaker.
Reverse its rotation.
Lower current and higher voltage.
25 feet.


19. 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.
A grounding resistor.
Nearly constant.
Squirrel-cage rotor.


20. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
No.6 AWG.
5:1.
Alternating current.
Zero amps.


21. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The motor rotation is reversed.
Check to make sure that the victim is not still in contact with the electricity.
H terminals.
Transformers.


22. Current transformers - or CT's - are used to...
Full-load - three-phase voltage.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
It provides good speed control.


23. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
Draw less current.
Isolation transformer.
Four times less than that of the secondary.


24. 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?
Current that changes constantly in magnitude and periodically in direction.
Squirrel-cage induction motor.
Zero amps.
100 turns.


25. 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?
Zero amps.
H terminals.
800 volts.
Capacitance.


26. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Inductance.
At least two phases
25 feet.
Lower current and higher voltage


27. The primary function of a power transformer is to provide...
The chest should rise or inflate.
Alternating current.
Grounded phase and ground fault devices were not operating.
Full-load - three-phase voltage.


28. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
60 Hertz
X.
The current will read zero.
25 feet.


29. Operating coils - motors - transformers - relays and solenoids depend upon...
7 -630 volts.
Draw less current.
Short-circuited after power has been removed.
Electro-magnetism for their operation.


30. How should clothing be removed from a burn?
Lower current and higher voltage.
Cut around clothing that has adhered to the burned area.
Reverse any two-phase leads.
Transformer


31. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
At least two phases
Provides single-phase power to smaller loads such as lights - heaters - etc.
150 turns.


32. A burn causing a blister is classified as a...
100 turns.
Second-degree burn.
X.
Full-load - three-phase voltage.


33. What type of 3-phase AC motor is used most often around a mine?
Lower current and higher voltage
Four times less than that of the secondary.
Carotid pulse - which is located in the neck next to the Adam's apple.
Squirrel-cage induction motor.


34. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Because less current flowing at high voltage causes less line loss per kilowatt.
15 feet off the ground.
600 volts.
X.


35. 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.
Stator windings.
75 turns.
Lower current and higher voltage.


36. Define alternating current...
200 volts AC.
The sum of the two capacitors.
Allow for metering voltage and Current.
Current changing constantly in magnitude and periodically in direction.


37. The property of an electric circuit that opposes any change in current is called...
Draw less current.
Inductance.
They should be made by the same manufacturer.
15 feet off the ground.


38. Not true about AC power?
Full-load - three-phase voltage.
It provides good speed control.
2000 watts
60 cycles per second (60 Hertz).


39. A solenoid coil is...
Reverse any two-phase leads.
An electromagnet.
H terminals.
Larger than that found in the primary winding.


40. AC voltage is raised or lowered by means of...
Transformers.
75 turns.
5:1.
Capacitance.


41. The main function of CT's and PT's on a main substation is to...
Nearly constant.
Allow for metering voltage and Current.
Draw less current.
12 to 15 times a minute.


42. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
100 volts.
X.
Reverse its rotation.
Inductance.


43. 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?
60 Hertz
Inductance.
75 turns.
A device used to store electrical energy.


44. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Full-load - three-phase voltage.
1 amp.
Short-circuited after power has been removed.
Stator windings.


45. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Circuit Breaker.
Cut around clothing that has adhered to the burned area.
The current will read zero.


46. What should the duty rating of a grounding resistor be?
Transformer
At least two phases
Continuous.
A device used to store electrical energy.


47. 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?
75 turns.
Squirrel-cage rotor.
X.
150 turns.


48. A control power transformer...
Inductance.
Four times less than that of the secondary.
No.6 AWG.
Provides single-phase power to smaller loads such as lights - heaters - etc.


49. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
They must be installed at least 7 feet above the ground.
150 turns.
A grounding resistor.
Capacitance.


50. The secondary windings on a 10:1 step-down transformer will have a wire size...
800 volts.
Larger than that found in the primary winding.
Current changing constantly in magnitude and periodically in direction.
277 volts.