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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. 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.
Transformer
Current changing constantly in magnitude and periodically in direction.
At the source transformer.

2. The property of an electric circuit that opposes any change in current is called...
Inductance.
100 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
At least two phases

3. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Inductance.
Stator windings.
Draw less current.
No.6 AWG.

4. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
Disconnect the frame-grounding conductor.
60 cycles per second (60 Hertz).
Draw less current.

5. Not a symptom of electrical shock?.
Grounded phase and ground fault devices were not operating.
Hyperventilation.
Electro-magnetism for their operation.
The current will read zero.

6. How do you change the direction of a 3-phase AC motor?
Second-degree burn.
Reverse its rotation.
Reverse any two-phase leads.
X.

7. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
5:1.
Draw less current.
277 volts.

8. Current in an AC circuit may be measured by...
Squirrel-cage rotor.
Clamp-on ammeter.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
75 turns.

9. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Lower current and higher voltage
Zero amps.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Nearly constant.

10. The main function of CT's and PT's on a main substation is to...
Reverse its rotation.
1 amp.
Potential transformer.
Allow for metering voltage and Current.

11. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
A.C.
Capacitance.
Four times less than that of the secondary.

12. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Inductance.
A.C.
Squirrel-cage rotor.

13. The transformer used only to measure voltage is a...
Potential transformer.
600 volts.
3 -979 Volts.
100 volts.

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

15. A solenoid coil is...
Inductance.
An electromagnet.
X.
The chest should rise or inflate.

16. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Circuit Breaker.
Inductance.
2000 watts
100 turns.

17. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
100 turns.
Check to make sure that the victim is not still in contact with the electricity.
Draw less current.

18. 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...
Allow for metering voltage and Current.
Tied together
Inductance.
Capacitance.

19. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
3 -979 Volts.
H terminals.
Grounded phase and ground fault devices were not operating.

20. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Four times less than that of the secondary.
The motor rotation is reversed.
Isolation transformer.
Nearly constant.

21. 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.
An electromagnet.
Carotid pulse - which is located in the neck next to the Adam's apple.
5:1
Lower current and higher voltage

22. The primary leads of a single-phase transformer should be connected to the...
Clamp-on ammeter.
H terminals.
No.6 AWG.
Lower current and higher voltage.

23. Compared to the secondary of a loaded - step-down transformer - the primary has...
A grounding resistor.
Lower current and higher voltage
A step-up transformer.
An electromagnet.

24. 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.
75 turns.
At the source transformer.
60 cycles per second (60 Hertz).

25. 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.
200 volts AC.
Grounded phase and ground fault devices were not operating.
Hyperventilation.

26. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The current will read zero.
Potential transformer.
Inductance.
A step-up transformer.

27. The primary function of a power transformer is to provide...
Allow for metering voltage and Current.
Transformers.
Full-load - three-phase voltage.
Continuous.

28. The combined capacitance of two capacitors in parallel is...
Lower current and higher voltage
Nearly constant.
The sum of the two capacitors.
Check to make sure that the victim is not still in contact with the electricity.

29. What is the first step to be followed in aiding a victim of electrical shock?
Current changing constantly in magnitude and periodically in direction.
Check to make sure that the victim is not still in contact with the electricity.
Because less current flowing at high voltage causes less line loss per kilowatt.
Tied together

30. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Reverse its rotation.
Inductance.
Two speeds
X.

31. Current that changes periodically in direction is...
Alternating current.
Circuit Breaker.
Inductance.
The sum of the two capacitors.

32. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
1 amp.
Full-load - three-phase voltage.
No.6 AWG.
Two speeds

33. 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?
1 amp.
No.6 AWG.
It provides good speed control.
75 turns.

34. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
2000 watts
7 -630 volts.
150 turns.

35. The purpose of a zig-zag transformer is to...
75 turns.
75 turns.
They should be made by the same manufacturer.
Derive a neutral for grounding purposes.

36. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
No.6 AWG.
Full-load - three-phase voltage.
60 cycles per second (60 Hertz).

37. If any two-phase wires are reversed on a three-phase motor - the motor will...
Larger than that found in the primary winding.
Reverse its rotation.
A.C.
They should be made by the same manufacturer.

38. The standard frequency of alternating current used at a mine is...
Carotid pulse - which is located in the neck next to the Adam's apple.
The current will read zero.
60 Hertz
Check to make sure that the victim is not still in contact with the electricity.

39. 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...
Draw less current.
A device used to store electrical energy.
Transformers.
An electromagnet.

40. 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.
An electromagnet.
The current will read zero.
75 turns.

41. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
A.C.
The capacitors should be discharged.
Disconnect the frame-grounding conductor.
100 volts.

42. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
75 turns.
150 turns.
Alternating current.

43. Operating coils - motors - transformers - relays and solenoids depend upon...
A.C.
Electro-magnetism for their operation.
Transformer
25 feet.

44. AC voltage is raised or lowered by means of...
Shunted and taped
Transformers.
Alternating current.
An electrical shock hazard may exist.

45. Alternating current may be defined as...
Four times less than that of the secondary.
Potential transformer.
H terminals.
Current that changes constantly in magnitude and periodically in direction.

46. All transformers step voltage up or down by...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Inductance.
No.6 AWG.
Shunted and taped

47. To protect against over-current in a three-phase circuit over-current protection must be provided for...
No.6 AWG.
At least two phases
Inductance.
Kilovolt ampere (KVA).

48. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Cut around clothing that has adhered to the burned area.
Current changing constantly in magnitude and periodically in direction.
7 -630 volts.
They must be installed at least 7 feet above the ground.

49. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
7 -630 volts.
1 amp.
A grounding resistor.
It provides good speed control.

50. A control power transformer...
Continuous.
A grounding resistor.
Circuit Breaker.
Provides single-phase power to smaller loads such as lights - heaters - etc.