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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 true about AC power?
The current will read zero.
Transformers.
75 turns.
It provides good speed control.

2. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Draw less current.
The current will read zero.
25 feet.

3. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
12 to 15 times a minute.
Larger than that found in the primary winding.
Tied together
Four times less than that of the secondary.

4. AC voltage is raised or lowered by means of...
Transformers.
Kilovolt ampere (KVA).
100 turns.
Larger than that found in the primary winding.

5. The speed of an alternating current - squirrel-cage induction motor is...
Disconnect the frame-grounding conductor.
Nearly constant.
75 turns.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

6. If any two-phase wires are reversed on a three-phase motor - the motor will...
The chest should rise or inflate.
Potential transformer.
Four times less than that of the secondary.
Reverse its rotation.

7. The transformer used only to measure voltage is a...
600 volts.
Potential transformer.
200 volts AC.
Four times less than that of the secondary.

8. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Potential transformer.
A device used to store electrical energy.
The capacitors should be discharged.

9. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Hyperventilation.
Two speeds
The chest should rise or inflate.
Disconnect the frame-grounding conductor.

10. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
The current will read zero.
600 volts.
480 volts.
25 feet.

11. Current in an AC circuit may be measured by...
Because less current flowing at high voltage causes less line loss per kilowatt.
Tied together
75 turns.
Clamp-on ammeter.

12. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Short-circuited after power has been removed.
75 turns.
Four times less than that of the secondary.
Clamp-on ammeter.

13. Where should grounding resistors be located?
A.C.
800 volts.
At the source transformer.
Kilovolt ampere (KVA).

14. Current transformers - or CT's - are used to...
Current changing constantly in magnitude and periodically in direction.
Electro-magnetism for their operation.
Four times less than that of the secondary.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

15. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
The sum of the two capacitors.
Alternating current.
Lower current and higher voltage.
2000 watts

16. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Transformers.
They should be made by the same manufacturer.
5:1.
Because less current flowing at high voltage causes less line loss per kilowatt.

17. Compared to the secondary of a loaded - step-down transformer - the primary has...
60 cycles per second (60 Hertz).
5:1
100 volts.
Lower current and higher voltage.

18. How do you change the direction of a 3-phase AC motor?
Draw less current.
Reverse any two-phase leads.
The sum of the two capacitors.
Squirrel-cage induction motor.

19. 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?
3 -979 Volts.
The capacitors should be discharged.
277 volts.
Shunted and taped

20. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
7 -630 volts.
Disconnect the frame-grounding conductor.
12 to 15 times a minute.
X.

21. The primary leads of a single-phase transformer should be connected to the...
Continuous.
Inductance.
H terminals.
Current that changes constantly in magnitude and periodically in direction.

22. Not an acceptable method for the installations of surface transformers?
5:1.
The capacitors should be discharged.
75 turns.
They must be installed at least 7 feet above the ground.

23. 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?
Four times less than that of the secondary.
No.6 AWG.
The current will read zero.
75 turns.

24. 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.
25 feet.
Shunted and taped

25. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Second-degree burn.
480 volts.
277 volts.
Cut around clothing that has adhered to the burned area.

26. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Isolation transformer.
Potential transformer.
A step-up transformer.
An electromagnet.

27. 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?
2000 watts
Allow for metering voltage and Current.
75 turns.
Capacitance.

28. A transformer with a 1:1 ratio is usually a (an)...
800 volts.
Check to make sure that the victim is not still in contact with the electricity.
Isolation transformer.
200 volts AC.

29. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Allow for metering voltage and Current.
Hyperventilation.
Shunted and taped

30. 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.
12 to 15 times a minute.
800 volts.
Clamp-on ammeter.

31. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
It provides good speed control.
Draw less current.
The current will read zero.
Derive a neutral for grounding purposes.

32. 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 any two-phase leads.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Tied together
The chest should rise or inflate.

33. Not a symptom of electrical shock?.
The sum of the two capacitors.
5:1
Hyperventilation.
The chest should rise or inflate.

34. Alternating current may be defined as...
The current will read zero.
Tied together
An electrical shock hazard may exist.
Current that changes constantly in magnitude and periodically in direction.

35. The purpose of a zig-zag transformer is to...
An electrical shock hazard may exist.
Derive a neutral for grounding purposes.
A.C.
Nearly constant.

36. 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.
Current changing constantly in magnitude and periodically in direction.
Cut around clothing that has adhered to the burned area.
200 volts AC.

37. 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.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The chest should rise or inflate.
Circuit Breaker.

38. How should clothing be removed from a burn?
It provides good speed control.
Short-circuited after power has been removed.
Cut around clothing that has adhered to the burned area.
Continuous.

39. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Shunted and taped
Short-circuited after power has been removed.
A grounding resistor.
Derive a neutral for grounding purposes.

40. What type motor is a wound-rotor induction motor?
15 feet off the ground.
Check to make sure that the victim is not still in contact with the electricity.
The chest should rise or inflate.
A.C.

41. The main function of CT's and PT's on a main substation is to...
Squirrel-cage rotor.
800 volts.
Allow for metering voltage and Current.
Derive a neutral for grounding purposes.

42. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Reverse its rotation.
Draw less current.
1 amp.
It provides good speed control.

43. 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?
Reverse any two-phase leads.
150 turns.
A grounding resistor.
An electrical shock hazard may exist.

44. Two 10-hp induction motors are operating on 460 volts AC. One motor is connected by single- phase; the other is connected in three-phase. The three-phase will...
1 amp.
Draw less current.
Short-circuited after power has been removed.
No.6 AWG.

45. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
The chest should rise or inflate.
Derive a neutral for grounding purposes.
100 turns.
Grounded phase and ground fault devices were not operating.

46. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
25 feet.
Potential transformer.
Cut around clothing that has adhered to the burned area.

47. The combined capacitance of two capacitors in parallel is...
Squirrel-cage induction motor.
The chest should rise or inflate.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The sum of the two capacitors.

48. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Capacitance.
5:1
7 -630 volts.
Continuous.

49. Current that changes periodically in direction is...
Alternating current.
25 feet.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Circuit Breaker.

50. 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.
1 amp.
A device used to store electrical energy.