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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. Not an acceptable method for the installations of surface transformers?
150 turns.
They must be installed at least 7 feet above the ground.
Lower current and higher voltage
7 -630 volts.

2. A solenoid coil is...
At least two phases
800 volts.
Squirrel-cage rotor.
An electromagnet.

3. 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?
75 turns.
600 volts.
Reverse its rotation.
Inductance.

4. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
60 cycles per second (60 Hertz).
Reverse any two-phase leads.
15 feet off the ground.
Two speeds

5. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Four times less than that of the secondary.
Reverse any two-phase leads.
Clamp-on ammeter.
480 volts.

6. At what rate should mouth-to-mouth resuscitation be applied?
3 -979 Volts.
12 to 15 times a minute.
15 feet off the ground.
75 turns.

7. What should the duty rating of a grounding resistor be?
The motor rotation is reversed.
Kilovolt ampere (KVA).
Continuous.
Full-load - three-phase voltage.

8. The combined capacitance of two capacitors in parallel is...
Zero amps.
60 cycles per second (60 Hertz).
The sum of the two capacitors.
200 volts AC.

9. The standard frequency of alternating current used at a mine is...
A step-up transformer.
Alternating current.
800 volts.
60 Hertz

10. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Short-circuited after power has been removed.
At least two phases
Provides single-phase power to smaller loads such as lights - heaters - etc.

11. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
Alternating current.
Hyperventilation.
Capacitance.

12. Not true about AC power?
Cut around clothing that has adhered to the burned area.
Clamp-on ammeter.
Grounded phase and ground fault devices were not operating.
It provides good speed control.

13. 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 step-up transformer.
150 turns.
The motor rotation is reversed.
100 volts.

14. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Transformer
The current will read zero.
12 to 15 times a minute.
Squirrel-cage induction motor.

15. 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.
The capacitors should be discharged.
5:1

16. What steps up or steps down AC voltage?
Transformer
Stator windings.
150 turns.
Grounded phase and ground fault devices were not operating.

17. The primary leads of a single-phase transformer should be connected to the...
Check to make sure that the victim is not still in contact with the electricity.
Derive a neutral for grounding purposes.
H terminals.
A grounding resistor.

18. 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...
600 volts.
Alternating current.
Inductance.
Draw less current.

19. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
An electromagnet.
X.
150 turns.
7 -630 volts.

20. How should clothing be removed from a burn?
H terminals.
480 volts.
Inductance.
Cut around clothing that has adhered to the burned area.

21. What is the danger when working around capacitors?
Lower current and higher voltage.
A.C.
An electrical shock hazard may exist.
600 volts.

22. 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?
75 turns.
At least two phases
They should be made by the same manufacturer.
Squirrel-cage rotor.

23. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Clamp-on ammeter.
They should be made by the same manufacturer.
Circuit Breaker.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

24. 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?
A device used to store electrical energy.
Lower current and higher voltage
1 amp.
200 volts AC.

25. 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
Derive a neutral for grounding purposes.
Draw less current.
Disconnect the frame-grounding conductor.

26. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
An electrical shock hazard may exist.
5:1.
100 volts.
The motor rotation is reversed.

27. The purpose of a zig-zag transformer is to...
A grounding resistor.
An electromagnet.
Derive a neutral for grounding purposes.
Carotid pulse - which is located in the neck next to the Adam's apple.

28. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Check to make sure that the victim is not still in contact with the electricity.
Alternating current.
Lower current and higher voltage.
1 amp.

29. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Four times less than that of the secondary.
Electro-magnetism for their operation.
Disconnect the frame-grounding conductor.

30. AC voltage is raised or lowered by means of...
Lower current and higher voltage
An electrical shock hazard may exist.
Transformers.
Current changing constantly in magnitude and periodically in direction.

31. Not a symptom of electrical shock?.
The motor rotation is reversed.
Reverse its rotation.
Draw less current.
Hyperventilation.

32. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Potential transformer.
Transformers.
A device used to store electrical energy.

33. All transformers step voltage up or down by...
Electro-magnetism for their operation.
A step-up transformer.
Inductance.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

34. 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.
At the source transformer.
Isolation transformer.
Short-circuited after power has been removed.

35. 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...
Squirrel-cage rotor.
100 volts.
Hyperventilation.
Squirrel-cage induction motor.

36. 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.
200 volts AC.
A grounding resistor.
5:1.
Grounded phase and ground fault devices were not operating.

37. The transformer used only to measure voltage is a...
Potential transformer.
No.6 AWG.
Because less current flowing at high voltage causes less line loss per kilowatt.
800 volts.

38. The property of an electrical circuit that opposes any change in voltage is called...
Shunted and taped
Capacitance.
X.
Squirrel-cage induction motor.

39. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
H terminals.
A grounding resistor.
800 volts.
1 amp.

40. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Full-load - three-phase voltage.
25 feet.
Two speeds
Grounded phase and ground fault devices were not operating.

41. Current that changes periodically in direction is...
The sum of the two capacitors.
The chest should rise or inflate.
Alternating current.
Current that changes constantly in magnitude and periodically in direction.

42. The primary function of a power transformer is to provide...
The capacitors should be discharged.
No.6 AWG.
Short-circuited after power has been removed.
Full-load - three-phase voltage.

43. How do you change the direction of a 3-phase AC motor?
Cut around clothing that has adhered to the burned area.
Reverse any two-phase leads.
Inductance.
Two speeds

44. A burn causing a blister is classified as a...
Second-degree burn.
600 volts.
Isolation transformer.
Squirrel-cage rotor.

45. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Nearly constant.
100 volts.
Inductance.
Two speeds

46. The main function of CT's and PT's on a main substation is to...
600 volts.
Electro-magnetism for their operation.
Allow for metering voltage and Current.
Disconnect the frame-grounding conductor.

47. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
They must be installed at least 7 feet above the ground.
A step-up transformer.
The chest should rise or inflate.
Stator windings.

48. 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...
The chest should rise or inflate.
Tied together
Carotid pulse - which is located in the neck next to the Adam's apple.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

49. A control power transformer...
5:1.
Current that changes constantly in magnitude and periodically in direction.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Derive a neutral for grounding purposes.

50. 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?
Continuous.
12 to 15 times a minute.
Because less current flowing at high voltage causes less line loss per kilowatt.
75 turns.