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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. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
Shunted and taped
Potential transformer.
200 volts AC.

2. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
The motor rotation is reversed.
Potential transformer.
Four times less than that of the secondary.
200 volts AC.

3. A wound-rotor induction motor has all the following EXCEPT...
Nearly constant.
Electro-magnetism for their operation.
Squirrel-cage rotor.
Provides single-phase power to smaller loads such as lights - heaters - etc.

4. What type motor is a wound-rotor induction motor?
Draw less current.
A.C.
Stator windings.
480 volts.

5. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Shunted and taped
7 -630 volts.
At least two phases
Grounded phase and ground fault devices were not operating.

6. Where should grounding resistors be located?
Second-degree burn.
600 volts.
At the source transformer.
The current will read zero.

7. Alternating current may be defined as...
The current will read zero.
Current that changes constantly in magnitude and periodically in direction.
X.
25 feet.

8. The primary function of a power transformer is to provide...
600 volts.
5:1.
Full-load - three-phase voltage.
Electro-magnetism for their operation.

9. 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?
H terminals.
100 turns.
The sum of the two capacitors.
Larger than that found in the primary winding.

10. What is the first step to be followed in aiding a victim of electrical shock?
Derive a neutral for grounding purposes.
Check to make sure that the victim is not still in contact with the electricity.
12 to 15 times a minute.
Lower current and higher voltage

11. Compared to the secondary of a loaded - step-down transformer - the primary has...
25 feet.
Hyperventilation.
The motor rotation is reversed.
Lower current and higher voltage.

12. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
600 volts.
Transformers.
The chest should rise or inflate.
At least two phases

13. When not connected to a load - the secondary leads of a current transformer should be...
Larger than that found in the primary winding.
Transformers.
Current that changes constantly in magnitude and periodically in direction.
Shunted and taped

14. Current that changes periodically in direction is...
They should be made by the same manufacturer.
Alternating current.
Electro-magnetism for their operation.
600 volts.

15. The combined capacitance of two capacitors in parallel is...
Potential transformer.
Isolation transformer.
Nearly constant.
The sum of the two capacitors.

16. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Inductance.
A device used to store electrical energy.
Short-circuited after power has been removed.
Check to make sure that the victim is not still in contact with the electricity.

17. The property of an electric circuit that opposes any change in current is called...
Transformers.
At the source transformer.
Hyperventilation.
Inductance.

18. 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.
An electrical shock hazard may exist.
X.
Kilovolt ampere (KVA).

19. Not true about AC power?
It provides good speed control.
Inductance.
Four times less than that of the secondary.
15 feet off the ground.

20. 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?
3 -979 Volts.
15 feet off the ground.
A grounding resistor.
800 volts.

21. 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...
Reverse its rotation.
Tied together
Provides single-phase power to smaller loads such as lights - heaters - etc.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

22. Operating coils - motors - transformers - relays and solenoids depend upon...
Current that changes constantly in magnitude and periodically in direction.
Four times less than that of the secondary.
Electro-magnetism for their operation.
Current changing constantly in magnitude and periodically in direction.

23. A burn causing a blister is classified as a...
Second-degree burn.
25 feet.
Check to make sure that the victim is not still in contact with the electricity.
60 Hertz

24. What should the duty rating of a grounding resistor be?
Lower current and higher voltage
Continuous.
The capacitors should be discharged.
Inductance.

25. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
100 turns.
X.
60 cycles per second (60 Hertz).
Lower current and higher voltage.

26. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
The chest should rise or inflate.
Disconnect the frame-grounding conductor.
Squirrel-cage rotor.
Hyperventilation.

27. Compared to the secondary of a loaded - step-down transformer - the primary has...
Because less current flowing at high voltage causes less line loss per kilowatt.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
600 volts.
Lower current and higher voltage

28. Which of the following does a squirrel cage induction motor have?
Provides single-phase power to smaller loads such as lights - heaters - etc.
At least two phases
Stator windings.
The chest should rise or inflate.

29. 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?
Squirrel-cage rotor.
75 turns.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
At the source transformer.

30. Current transformers - or CT's - are used to...
A grounding resistor.
The motor rotation is reversed.
Draw less current.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

31. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Zero amps.
2000 watts
H terminals.
Second-degree burn.

32. 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...
Draw less current.
100 volts.
Two speeds
Provides single-phase power to smaller loads such as lights - heaters - etc.

33. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Draw less current.
They must be installed at least 7 feet above the ground.
Zero amps.
X.

34. The size of a transformer is measured in...
100 turns.
They should be made by the same manufacturer.
Kilovolt ampere (KVA).
The chest should rise or inflate.

35. 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?
100 turns.
The current will read zero.
Clamp-on ammeter.
200 volts AC.

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
The motor rotation is reversed.
Lower current and higher voltage.
1 amp.

37. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
No.6 AWG.
Inductance.
Current changing constantly in magnitude and periodically in direction.

38. The transformer used only to measure voltage is a...
150 turns.
Potential transformer.
25 feet.
The current will read zero.

39. Not a symptom of electrical shock?.
Inductance.
Hyperventilation.
60 Hertz
Draw less current.

40. The secondary windings on a 10:1 step-down transformer will have a wire size...
Hyperventilation.
Larger than that found in the primary winding.
Alternating current.
Stator windings.

41. Three-phase AC underground cables must be provided with overcurrent protection using a...
Clamp-on ammeter.
Disconnect the frame-grounding conductor.
600 volts.
Circuit Breaker.

42. A solenoid coil is...
Potential transformer.
An electromagnet.
Larger than that found in the primary winding.
75 turns.

43. What is a capacitor?
Potential transformer.
7 -630 volts.
It provides good speed control.
A device used to store electrical energy.

44. What type of 3-phase AC motor is used most often around a mine?
Clamp-on ammeter.
Squirrel-cage induction motor.
100 turns.
Short-circuited after power has been removed.

45. 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.
It provides good speed control.
Kilovolt ampere (KVA).
Cut around clothing that has adhered to the burned area.

46. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
No.6 AWG.
Shunted and taped
Continuous.

47. 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...
Transformers.
100 volts.
1 amp.
An electrical shock hazard may exist.

48. If any two-phase wires are reversed on a three-phase motor - the motor will...
5:1
1 amp.
Reverse its rotation.
100 volts.

49. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
The chest should rise or inflate.
75 turns.
Full-load - three-phase voltage.

50. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
A step-up transformer.
Two speeds
800 volts.
Potential transformer.