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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. Three-phase AC underground cables must be provided with overcurrent protection using a...
Second-degree burn.
Circuit Breaker.
Lower current and higher voltage.
Inductance.

2. 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.
The capacitors should be discharged.
Full-load - three-phase voltage.
Provides single-phase power to smaller loads such as lights - heaters - etc.

3. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Because less current flowing at high voltage causes less line loss per kilowatt.
Nearly constant.
Two speeds
A grounding resistor.

4. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Inductance.
Inductance.
150 turns.

5. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Carotid pulse - which is located in the neck next to the Adam's apple.
Alternating current.
Squirrel-cage rotor.

6. The primary leads of a single-phase transformer should be connected to the...
It provides good speed control.
150 turns.
H terminals.
Lower current and higher voltage

7. A control power transformer...
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.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Shunted and taped

8. What type motor is a wound-rotor induction motor?
5:1.
A.C.
Lower current and higher voltage
Because less current flowing at high voltage causes less line loss per kilowatt.

9. The primary function of a power transformer is to provide...
480 volts.
Potential transformer.
At the source transformer.
Full-load - three-phase voltage.

10. The combined capacitance of two capacitors in parallel is...
Electro-magnetism for their operation.
The sum of the two capacitors.
An electromagnet.
The motor rotation is reversed.

11. 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?
A device used to store electrical energy.
Two speeds
800 volts.
At least two phases

12. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The motor rotation is reversed.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The chest should rise or inflate.
100 turns.

13. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
60 Hertz
Potential transformer.
Check to make sure that the victim is not still in contact with the electricity.
7 -630 volts.

14. 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...
2000 watts
Shunted and taped
100 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

15. What is a capacitor?
15 feet off the ground.
A device used to store electrical energy.
A.C.
600 volts.

16. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
600 volts.
Lower current and higher voltage
Short-circuited after power has been removed.
Inductance.

17. 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.
5:1
Two speeds
Lower current and higher voltage
Squirrel-cage induction motor.

18. To protect against over-current in a three-phase circuit over-current protection must be provided for...
1 amp.
Squirrel-cage rotor.
H terminals.
At least two phases

19. Alternating current may be defined as...
At the source transformer.
Current that changes constantly in magnitude and periodically in direction.
Circuit Breaker.
The motor rotation is reversed.

20. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
A grounding resistor.
An electromagnet.
Disconnect the frame-grounding conductor.

21. The main function of CT's and PT's on a main substation is to...
Disconnect the frame-grounding conductor.
Nearly constant.
Allow for metering voltage and Current.
600 volts.

22. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
150 turns.
600 volts.
Nearly constant.

23. The secondary windings on a 10:1 step-down transformer will have a wire size...
Squirrel-cage induction motor.
Transformers.
Larger than that found in the primary winding.
5:1.

24. The standard frequency of alternating current used at a mine is...
Draw less current.
Transformers.
Shunted and taped
60 Hertz

25. Current transformers - or CT's - are used to...
It provides good speed control.
Nearly constant.
Current changing constantly in magnitude and periodically in direction.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

26. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
2000 watts
200 volts AC.
Continuous.
277 volts.

27. What is the danger when working around capacitors?
A grounding resistor.
An electrical shock hazard may exist.
Potential transformer.
Transformers.

28. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
They must be installed at least 7 feet above the ground.
Transformer

29. Current in an AC circuit may be measured by...
25 feet.
Clamp-on ammeter.
600 volts.
Draw less current.

30. 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.
Four times less than that of the secondary.
At least two phases
A step-up transformer.

31. 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?
Squirrel-cage induction motor.
At the source transformer.
The chest should rise or inflate.
600 volts.

32. What steps up or steps down AC voltage?
12 to 15 times a minute.
75 turns.
Transformer
H terminals.

33. Not true about AC power?
100 volts.
Grounded phase and ground fault devices were not operating.
A grounding resistor.
It provides good speed control.

34. The transformer used only to measure voltage is a...
Draw less current.
60 Hertz
Provides single-phase power to smaller loads such as lights - heaters - etc.
Potential transformer.

35. A transformer with a 1:1 ratio is usually a (an)...
150 turns.
Isolation transformer.
480 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

36. What type of 3-phase AC motor is used most often around a mine?
Four times less than that of the secondary.
Squirrel-cage induction motor.
60 Hertz
A grounding resistor.

37. If any two-phase wires are reversed on a three-phase motor - the motor will...
At least two phases
Reverse its rotation.
7 -630 volts.
Zero amps.

38. Current that changes periodically in direction is...
Shunted and taped
Alternating current.
Second-degree burn.
Lower current and higher voltage.

39. Compared to the secondary of a loaded - step-down transformer - the primary has...
277 volts.
Squirrel-cage rotor.
Second-degree burn.
Lower current and higher voltage.

40. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Draw less current.
A step-up transformer.
A grounding resistor.
Squirrel-cage rotor.

41. The speed of an alternating current - squirrel-cage induction motor is...
1 amp.
12 to 15 times a minute.
Nearly constant.
Transformer

42. What should the duty rating of a grounding resistor be?
Continuous.
Electro-magnetism for their operation.
At the source transformer.
H terminals.

43. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
Potential transformer.
Transformer
Carotid pulse - which is located in the neck next to the Adam's apple.

44. A solenoid coil is...
Cut around clothing that has adhered to the burned area.
Reverse any two-phase leads.
An electromagnet.
5:1

45. The size of a transformer is measured in...
60 Hertz
Transformer
Isolation transformer.
Kilovolt ampere (KVA).

46. Not an acceptable method for the installations of surface transformers?
Squirrel-cage rotor.
Grounded phase and ground fault devices were not operating.
An electromagnet.
They must be installed at least 7 feet above the ground.

47. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
X.
Derive a neutral for grounding purposes.
Clamp-on ammeter.

48. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
A.C.
Four times less than that of the secondary.
No.6 AWG.
Reverse its rotation.

49. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Kilovolt ampere (KVA).
2000 watts
H terminals.
Disconnect the frame-grounding conductor.

50. Not a symptom of electrical shock?.
Hyperventilation.
Four times less than that of the secondary.
277 volts.
Reverse any two-phase leads.