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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 main function of CT's and PT's on a main substation is to...
Grounded phase and ground fault devices were not operating.
Current that changes constantly in magnitude and periodically in direction.
Allow for metering voltage and Current.
A step-up transformer.

2. 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?
An electrical shock hazard may exist.
Inductance.
They should be made by the same manufacturer.
100 turns.

3. How do you change the direction of a 3-phase AC motor?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Circuit Breaker.
277 volts.
Reverse any two-phase leads.

4. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Nearly constant.
Shunted and taped
Draw less current.
277 volts.

5. When not connected to a load - the secondary leads of a current transformer should be...
Clamp-on ammeter.
Derive a neutral for grounding purposes.
Shunted and taped
Short-circuited after power has been removed.

6. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Transformers.
200 volts AC.
Four times less than that of the secondary.
1 amp.

7. A transformer with a 1:1 ratio is usually a (an)...
Inductance.
Tied together
Isolation transformer.
X.

8. Not an acceptable method for the installations of surface transformers?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
5:1
Allow for metering voltage and Current.
They must be installed at least 7 feet above the ground.

9. Current that changes periodically in direction is...
Potential transformer.
Alternating current.
Reverse any two-phase leads.
Tied together

10. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
The capacitors should be discharged.
Electro-magnetism for their operation.
Short-circuited after power has been removed.

11. Define alternating current...
Kilovolt ampere (KVA).
A.C.
100 turns.
Current changing constantly in magnitude and periodically in direction.

12. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
They should be made by the same manufacturer.
Hyperventilation.
An electrical shock hazard may exist.
The current will read zero.

13. Which of the following does a squirrel cage induction motor have?
60 cycles per second (60 Hertz).
Stator windings.
60 Hertz
No.6 AWG.

14. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Transformer
75 turns.
Lower current and higher voltage.
X.

15. 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.
At least two phases
Stator windings.
Squirrel-cage induction motor.

16. 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?
Circuit Breaker.
100 volts.
150 turns.
3 -979 Volts.

17. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Reverse any two-phase leads.
Circuit Breaker.
The chest should rise or inflate.

18. Three-phase AC underground cables must be provided with overcurrent protection using a...
Nearly constant.
Circuit Breaker.
Lower current and higher voltage
A device used to store electrical energy.

19. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
A.C.
Squirrel-cage induction motor.
Draw less current.

20. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
1 amp.
Four times less than that of the secondary.
Full-load - three-phase voltage.
A grounding resistor.

21. Where should grounding resistors be located?
At the source transformer.
800 volts.
2000 watts
200 volts AC.

22. What type motor is a wound-rotor induction motor?
Squirrel-cage rotor.
12 to 15 times a minute.
A.C.
Two speeds

23. All transformers step voltage up or down by...
Inductance.
The motor rotation is reversed.
Zero amps.
Reverse any two-phase leads.

24. Operating coils - motors - transformers - relays and solenoids depend upon...
Because less current flowing at high voltage causes less line loss per kilowatt.
Electro-magnetism for their operation.
75 turns.
Allow for metering voltage and Current.

25. Current transformers - or CT's - are used to...
25 feet.
Current that changes constantly in magnitude and periodically in direction.
Shunted and taped
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

26. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Tied together
60 cycles per second (60 Hertz).
800 volts.

27. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Transformers.
5:1.
Inductance.
Short-circuited after power has been removed.

28. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
15 feet off the ground.
Tied together
Disconnect the frame-grounding conductor.
Two speeds

29. If any two-phase wires are reversed on a three-phase motor - the motor will...
Carotid pulse - which is located in the neck next to the Adam's apple.
It provides good speed control.
Clamp-on ammeter.
Reverse its rotation.

30. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
7 -630 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
A.C.

31. 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.
800 volts.
Squirrel-cage induction motor.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

32. What is a capacitor?
The chest should rise or inflate.
1 amp.
The capacitors should be discharged.
A device used to store electrical energy.

33. A solenoid coil is...
A grounding resistor.
Squirrel-cage rotor.
An electromagnet.
Shunted and taped

34. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Hyperventilation.
The motor rotation is reversed.
480 volts.
Zero amps.

35. The property of an electric circuit that opposes any change in current is called...
Lower current and higher voltage
60 cycles per second (60 Hertz).
The chest should rise or inflate.
Inductance.

36. The size of a transformer is measured in...
Kilovolt ampere (KVA).
Grounded phase and ground fault devices were not operating.
600 volts.
A grounding resistor.

37. 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...
Potential transformer.
Tied together
100 volts.
Stator windings.

38. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Hyperventilation.
Grounded phase and ground fault devices were not operating.
Short-circuited after power has been removed.
Isolation transformer.

39. 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.
Stator windings.
Tied together
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

40. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
75 turns.
Short-circuited after power has been removed.
Transformers.

41. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
They should be made by the same manufacturer.
Lower current and higher voltage
Hyperventilation.
Kilovolt ampere (KVA).

42. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
Reverse its rotation.
Allow for metering voltage and Current.
A.C.

43. Not true about AC power?
800 volts.
Nearly constant.
Circuit Breaker.
It provides good speed control.

44. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
They should be made by the same manufacturer.
The chest should rise or inflate.
1 amp.
7 -630 volts.

45. 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
Squirrel-cage rotor.
3 -979 Volts.
The chest should rise or inflate.

46. 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?
Current changing constantly in magnitude and periodically in direction.
Stator windings.
800 volts.
1 amp.

47. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Second-degree burn.
Allow for metering voltage and Current.
Four times less than that of the secondary.

48. Alternating current may be defined as...
Draw less current.
Current that changes constantly in magnitude and periodically in direction.
Draw less current.
Continuous.

49. The primary leads of a single-phase transformer should be connected to the...
Larger than that found in the primary winding.
H terminals.
Disconnect the frame-grounding conductor.
200 volts AC.

50. 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.
The motor rotation is reversed.
The chest should rise or inflate.
Cut around clothing that has adhered to the burned area.