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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. 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
150 turns.
X.
At the source transformer.

2. 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?
800 volts.
Stator windings.
Inductance.
3 -979 Volts.

3. What is the first step to be followed in aiding a victim of electrical shock?
Check to make sure that the victim is not still in contact with the electricity.
Isolation transformer.
200 volts AC.
X.

4. The property of an electric circuit that opposes any change in current is called...
Kilovolt ampere (KVA).
Reverse its rotation.
Current that changes constantly in magnitude and periodically in direction.
Inductance.

5. 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?
100 turns.
5:1
600 volts.
Squirrel-cage induction motor.

6. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
A.C.
Cut around clothing that has adhered to the burned area.
200 volts AC.

7. All transformers step voltage up or down by...
Second-degree burn.
A step-up transformer.
Inductance.
Electro-magnetism for their operation.

8. 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.
60 Hertz
Potential transformer.

9. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Draw less current.
200 volts AC.
Allow for metering voltage and Current.
A step-up transformer.

10. A burn causing a blister is classified as a...
Reverse its rotation.
Second-degree burn.
Alternating current.
Squirrel-cage induction motor.

11. The speed of an alternating current - squirrel-cage induction motor is...
No.6 AWG.
Short-circuited after power has been removed.
Nearly constant.
Because less current flowing at high voltage causes less line loss per kilowatt.

12. Current that changes periodically in direction is...
Draw less current.
Transformers.
2000 watts
Alternating current.

13. Where should grounding resistors be located?
7 -630 volts.
At the source transformer.
Check to make sure that the victim is not still in contact with the electricity.
An electromagnet.

14. The primary leads of a single-phase transformer should be connected to the...
A device used to store electrical energy.
The current will read zero.
H terminals.
Cut around clothing that has adhered to the burned area.

15. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
X.
The sum of the two capacitors.
The chest should rise or inflate.

16. The main function of CT's and PT's on a main substation is to...
The capacitors should be discharged.
12 to 15 times a minute.
Kilovolt ampere (KVA).
Allow for metering voltage and Current.

17. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
A device used to store electrical energy.
The capacitors should be discharged.
Potential transformer.
60 cycles per second (60 Hertz).

18. To protect against over-current in a three-phase circuit over-current protection must be provided for...
3 -979 Volts.
At least two phases
5:1.
Carotid pulse - which is located in the neck next to the Adam's apple.

19. The purpose of a zig-zag transformer is to...
75 turns.
Two speeds
Derive a neutral for grounding purposes.
No.6 AWG.

20. 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?
A.C.
150 turns.
X.
The motor rotation is reversed.

21. How should clothing be removed from a burn?
The current will read zero.
200 volts AC.
Cut around clothing that has adhered to the burned area.
Isolation transformer.

22. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Inductance.
H terminals.
2000 watts
3 -979 Volts.

23. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Inductance.
The chest should rise or inflate.
Current that changes constantly in magnitude and periodically in direction.
Four times less than that of the secondary.

24. If any two-phase wires are reversed on a three-phase motor - the motor will...
Hyperventilation.
Reverse its rotation.
Squirrel-cage rotor.
Four times less than that of the secondary.

25. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
60 Hertz
Tied together
Because less current flowing at high voltage causes less line loss per kilowatt.
The motor rotation is reversed.

26. How do you change the direction of a 3-phase AC motor?
Squirrel-cage rotor.
480 volts.
Reverse any two-phase leads.
Squirrel-cage induction motor.

27. A solenoid coil is...
5:1
H terminals.
An electromagnet.
Squirrel-cage rotor.

28. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
Inductance.
Circuit Breaker.
The current will read zero.

29. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Nearly constant.
150 turns.
X.

30. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
The chest should rise or inflate.
They must be installed at least 7 feet above the ground.
An electromagnet.

31. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
At least two phases
60 cycles per second (60 Hertz).
Disconnect the frame-grounding conductor.
100 turns.

32. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
A.C.
It provides good speed control.
Full-load - three-phase voltage.
15 feet off the ground.

33. What is a capacitor?
They must be installed at least 7 feet above the ground.
A device used to store electrical energy.
They should be made by the same manufacturer.
Provides single-phase power to smaller loads such as lights - heaters - etc.

34. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
75 turns.
25 feet.
A grounding resistor.
75 turns.

35. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
The motor rotation is reversed.
They should be made by the same manufacturer.
Zero amps.
2000 watts

36. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
12 to 15 times a minute.
The capacitors should be discharged.
Two speeds
Carotid pulse - which is located in the neck next to the Adam's apple.

37. The primary function of a power transformer is to provide...
100 volts.
Cut around clothing that has adhered to the burned area.
Full-load - three-phase voltage.
Continuous.

38. What type motor is a wound-rotor induction motor?
Tied together
Kilovolt ampere (KVA).
480 volts.
A.C.

39. Which of the following does a squirrel cage induction motor have?
The chest should rise or inflate.
Carotid pulse - which is located in the neck next to the Adam's apple.
Lower current and higher voltage
Stator windings.

40. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
A.C.
Continuous.
Transformer

41. Compared to the secondary of a loaded - step-down transformer - the primary has...
25 feet.
Because less current flowing at high voltage causes less line loss per kilowatt.
Lower current and higher voltage
Inductance.

42. The transformer used only to measure voltage is a...
Reverse any two-phase leads.
Potential transformer.
Check to make sure that the victim is not still in contact with the electricity.
An electromagnet.

43. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Cut around clothing that has adhered to the burned area.
Draw less current.
Zero amps.
A device used to store electrical energy.

44. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Check to make sure that the victim is not still in contact with the electricity.
Draw less current.
480 volts.
A.C.

45. Under fault conditions - the grounding resistor in a high voltage circuit limits the voltage drop in the grounding circuit external to the resistor to not more than...
Inductance.
100 volts.
Lower current and higher voltage.
Lower current and higher voltage

46. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
277 volts.
Four times less than that of the secondary.
Hyperventilation.
Stator windings.

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

48. What is the danger when working around capacitors?
H terminals.
Derive a neutral for grounding purposes.
150 turns.
An electrical shock hazard may exist.

49. The combined capacitance of two capacitors in parallel is...
Second-degree burn.
The sum of the two capacitors.
An electromagnet.
Because less current flowing at high voltage causes less line loss per kilowatt.

50. 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?
Reverse any two-phase leads.
Inductance.
800 volts.
Reverse its rotation.