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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. Where should grounding resistors be located?
At the source transformer.
480 volts.
A grounding resistor.
Transformers.

2. A solenoid coil is...
An electromagnet.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
X.
480 volts.

3. The purpose of a zig-zag transformer is to...
Hyperventilation.
Derive a neutral for grounding purposes.
H terminals.
5:1

4. The speed of an alternating current - squirrel-cage induction motor is...
Carotid pulse - which is located in the neck next to the Adam's apple.
480 volts.
25 feet.
Nearly constant.

5. Operating coils - motors - transformers - relays and solenoids depend upon...
800 volts.
Electro-magnetism for their operation.
Tied together
Kilovolt ampere (KVA).

6. 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.
They must be installed at least 7 feet above the ground.
Larger than that found in the primary winding.
150 turns.

7. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Grounded phase and ground fault devices were not operating.
The motor rotation is reversed.
5:1.
Clamp-on ammeter.

8. 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.
A grounding resistor.
Because less current flowing at high voltage causes less line loss per kilowatt.
Full-load - three-phase voltage.
5:1.

9. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
2000 watts
X.
100 volts.
Clamp-on ammeter.

10. The primary leads of a single-phase transformer should be connected to the...
Current changing constantly in magnitude and periodically in direction.
H terminals.
3 -979 Volts.
Four times less than that of the secondary.

11. AC voltage is raised or lowered by means of...
Inductance.
Current changing constantly in magnitude and periodically in direction.
2000 watts
Transformers.

12. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
100 volts.
Two speeds
H terminals.

13. The main function of CT's and PT's on a main substation is to...
At least two phases
They must be installed at least 7 feet above the ground.
5:1
Allow for metering voltage and Current.

14. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Zero amps.
Provides single-phase power to smaller loads such as lights - heaters - etc.
A grounding resistor.
Larger than that found in the primary winding.

15. Three-phase AC underground cables must be provided with overcurrent protection using a...
An electromagnet.
Kilovolt ampere (KVA).
Circuit Breaker.
The motor rotation is reversed.

16. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
800 volts.
Squirrel-cage induction motor.
X.
7 -630 volts.

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

18. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Stator windings.
1 amp.
Allow for metering voltage and Current.
150 turns.

19. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
5:1.
Check to make sure that the victim is not still in contact with the electricity.
Transformer

20. The primary function of a power transformer is to provide...
Continuous.
Grounded phase and ground fault devices were not operating.
Full-load - three-phase voltage.
Larger than that found in the primary winding.

21. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
Four times less than that of the secondary.
480 volts.
5:1.

22. 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.
Inductance.
Squirrel-cage induction motor.
They should be made by the same manufacturer.

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?
An electromagnet.
Lower current and higher voltage.
100 turns.
Shunted and taped

24. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
7 -630 volts.
480 volts.
Full-load - three-phase voltage.
Tied together

25. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Allow for metering voltage and Current.
15 feet off the ground.
75 turns.
600 volts.

26. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
5:1
Shunted and taped
Hyperventilation.

27. Current transformers - or CT's - are used to...
Current that changes constantly in magnitude and periodically in direction.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Grounded phase and ground fault devices were not operating.
They must be installed at least 7 feet above the ground.

28. 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...
At least two phases
5:1.
A device used to store electrical energy.
Draw less current.

29. 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.
Reverse any two-phase leads.
Squirrel-cage rotor.
5:1
600 volts.

30. What is the danger when working around capacitors?
Capacitance.
A step-up transformer.
An electrical shock hazard may exist.
Derive a neutral for grounding purposes.

31. How do you change the direction of a 3-phase AC motor?
The chest should rise or inflate.
Reverse any two-phase leads.
It provides good speed control.
75 turns.

32. A transformer with a 1:1 ratio is usually a (an)...
Capacitance.
800 volts.
25 feet.
Isolation transformer.

33. The property of an electrical circuit that opposes any change in voltage is called...
15 feet off the ground.
Capacitance.
Clamp-on ammeter.
A step-up transformer.

34. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
600 volts.
5:1.
X.
A step-up transformer.

35. The transformer used only to measure voltage is a...
Potential transformer.
5:1.
A grounding resistor.
60 cycles per second (60 Hertz).

36. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Grounded phase and ground fault devices were not operating.
The chest should rise or inflate.
At least two phases
A device used to store electrical energy.

37. 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?
75 turns.
Capacitance.
H terminals.
They must be installed at least 7 feet above the ground.

38. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
Disconnect the frame-grounding conductor.
It provides good speed control.
Reverse any two-phase leads.

39. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Derive a neutral for grounding purposes.
Short-circuited after power has been removed.
A device used to store electrical energy.
Larger than that found in the primary winding.

40. Which of the following does a squirrel cage induction motor have?
An electromagnet.
The chest should rise or inflate.
Stator windings.
X.

41. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
150 turns.
Four times less than that of the secondary.
Two speeds
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

42. Alternating current may be defined as...
Cut around clothing that has adhered to the burned area.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Current that changes constantly in magnitude and periodically in direction.
Short-circuited after power has been removed.

43. A wound-rotor induction motor has all the following EXCEPT...
75 turns.
An electrical shock hazard may exist.
12 to 15 times a minute.
Squirrel-cage rotor.

44. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Capacitance.
800 volts.
7 -630 volts.

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

46. To protect against over-current in a three-phase circuit over-current protection must be provided for...
3 -979 Volts.
Reverse its rotation.
At least two phases
A.C.

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...
75 turns.
Allow for metering voltage and Current.
2000 watts
100 volts.

48. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Because less current flowing at high voltage causes less line loss per kilowatt.
480 volts.
A device used to store electrical energy.
Disconnect the frame-grounding conductor.

49. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
7 -630 volts.
The current will read zero.
Squirrel-cage induction motor.
Check to make sure that the victim is not still in contact with the electricity.

50. 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.
75 turns.
Continuous.
60 cycles per second (60 Hertz).