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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. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
277 volts.
7 -630 volts.
Transformers.
Current changing constantly in magnitude and periodically in direction.

2. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
150 turns.
1 amp.
No.6 AWG.
Shunted and taped

3. 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?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
3 -979 Volts.
12 to 15 times a minute.
Nearly constant.

4. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
75 turns.
60 cycles per second (60 Hertz).
Short-circuited after power has been removed.
800 volts.

5. Current in an AC circuit may be measured by...
Electro-magnetism for their operation.
5:1.
Clamp-on ammeter.
Lower current and higher voltage.

6. Not a symptom of electrical shock?.
Hyperventilation.
A.C.
Nearly constant.
277 volts.

7. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Electro-magnetism for their operation.
X.
Squirrel-cage rotor.
Two speeds

8. High voltage is used to transmit power over long distances...
An electromagnet.
At least two phases
Capacitance.
Because less current flowing at high voltage causes less line loss per kilowatt.

9. 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...
7 -630 volts.
At the source transformer.
Tied together
480 volts.

10. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Squirrel-cage rotor.
Disconnect the frame-grounding conductor.
A.C.
Four times less than that of the secondary.

11. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Grounded phase and ground fault devices were not operating.
7 -630 volts.
X.
No.6 AWG.

12. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Inductance.
2000 watts
The current will read zero.
100 turns.

13. 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?
The sum of the two capacitors.
100 turns.
The capacitors should be discharged.
800 volts.

14. 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.
25 feet.
Nearly constant.
5:1
Lower current and higher voltage.

15. 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.
Lower current and higher voltage
X.
Current that changes constantly in magnitude and periodically in direction.

16. The secondary windings on a 10:1 step-down transformer will have a wire size...
7 -630 volts.
Larger than that found in the primary winding.
The sum of the two capacitors.
Inductance.

17. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Alternating current.
200 volts AC.
5:1

18. Define alternating current...
Zero amps.
Current changing constantly in magnitude and periodically in direction.
Second-degree burn.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

19. The property of an electrical circuit that opposes any change in voltage is called...
Inductance.
Squirrel-cage rotor.
Capacitance.
1 amp.

20. Alternating current may be defined as...
5:1
Inductance.
Current that changes constantly in magnitude and periodically in direction.
Shunted and taped

21. Current that changes periodically in direction is...
Alternating current.
200 volts AC.
Squirrel-cage induction motor.
Zero amps.

22. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
600 volts.
800 volts.
Check to make sure that the victim is not still in contact with the electricity.

23. 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.
Circuit Breaker.
Shunted and taped
The motor rotation is reversed.
5:1.

24. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
12 to 15 times a minute.
A grounding resistor.
Disconnect the frame-grounding conductor.
Reverse any two-phase leads.

25. What is the danger when working around capacitors?
An electrical shock hazard may exist.
A step-up transformer.
Full-load - three-phase voltage.
It provides good speed control.

26. All transformers step voltage up or down by...
Check to make sure that the victim is not still in contact with the electricity.
Inductance.
Tied together
The motor rotation is reversed.

27. How should clothing be removed from a burn?
Alternating current.
5:1
Continuous.
Cut around clothing that has adhered to the burned area.

28. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Stator windings.
H terminals.
600 volts.

29. The transformer used only to measure voltage is a...
Reverse its rotation.
75 turns.
Potential transformer.
12 to 15 times a minute.

30. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
277 volts.
They should be made by the same manufacturer.
200 volts AC.
It provides good speed control.

31. The combined capacitance of two capacitors in parallel is...
A step-up transformer.
Clamp-on ammeter.
Current changing constantly in magnitude and periodically in direction.
The sum of the two capacitors.

32. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Larger than that found in the primary winding.
A grounding resistor.
Disconnect the frame-grounding conductor.

33. The property of an electric circuit that opposes any change in current is called...
It provides good speed control.
12 to 15 times a minute.
Inductance.
Electro-magnetism for their operation.

34. AC voltage is raised or lowered by means of...
Transformers.
Draw less current.
60 cycles per second (60 Hertz).
Hyperventilation.

35. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Transformer
Isolation transformer.
150 turns.

36. The standard frequency of alternating current used at a mine is...
Allow for metering voltage and Current.
60 Hertz
X.
No.6 AWG.

37. Operating coils - motors - transformers - relays and solenoids depend upon...
Lower current and higher voltage
600 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
Electro-magnetism for their operation.

38. The size of a transformer is measured in...
Short-circuited after power has been removed.
Shunted and taped
Kilovolt ampere (KVA).
Cut around clothing that has adhered to the burned area.

39. Compared to the secondary of a loaded - step-down transformer - the primary has...
Capacitance.
The current will read zero.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Lower current and higher voltage.

40. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Because less current flowing at high voltage causes less line loss per kilowatt.
Transformers.
Larger than that found in the primary winding.
They should be made by the same manufacturer.

41. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Four times less than that of the secondary.
Nearly constant.
At least two phases
Kilovolt ampere (KVA).

42. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
100 volts.
Lower current and higher voltage.
Zero amps.
Grounded phase and ground fault devices were not operating.

43. 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?
Shunted and taped
75 turns.
No.6 AWG.
Isolation transformer.

44. A control power transformer...
Transformer
Provides single-phase power to smaller loads such as lights - heaters - etc.
Inductance.
Disconnect the frame-grounding conductor.

45. A solenoid coil is...
5:1
An electromagnet.
60 cycles per second (60 Hertz).
Alternating current.

46. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Clamp-on ammeter.
An electromagnet.
1 amp.
A.C.

47. What steps up or steps down AC voltage?
150 turns.
Current changing constantly in magnitude and periodically in direction.
Inductance.
Transformer

48. The purpose of a zig-zag transformer is to...
100 volts.
H terminals.
Derive a neutral for grounding purposes.
Two speeds

49. 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...
100 volts.
60 Hertz
Continuous.
Derive a neutral for grounding purposes.

50. The standard frequency of power supplied by the power company is...
Circuit Breaker.
60 cycles per second (60 Hertz).
Clamp-on ammeter.
A grounding resistor.