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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 control power transformer...
A device used to store electrical energy.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Transformer
Provides single-phase power to smaller loads such as lights - heaters - etc.

2. If any two-phase wires are reversed on a three-phase motor - the motor will...
Allow for metering voltage and Current.
Disconnect the frame-grounding conductor.
Reverse its rotation.
60 cycles per second (60 Hertz).

3. What type of 3-phase AC motor is used most often around a mine?
100 turns.
Grounded phase and ground fault devices were not operating.
Squirrel-cage induction motor.
The sum of the two capacitors.

4. 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?
A grounding resistor.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
3 -979 Volts.
60 Hertz

5. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
At least two phases
5:1.
Lower current and higher voltage.

6. Define alternating current...
800 volts.
Current changing constantly in magnitude and periodically in direction.
The current will read zero.
Draw less current.

7. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Reverse any two-phase leads.
They should be made by the same manufacturer.
They must be installed at least 7 feet above the ground.

8. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Circuit Breaker.
Nearly constant.
Provides single-phase power to smaller loads such as lights - heaters - etc.

9. AC voltage is raised or lowered by means of...
Transformers.
A grounding resistor.
Carotid pulse - which is located in the neck next to the Adam's apple.
Capacitance.

10. 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...
Provides single-phase power to smaller loads such as lights - heaters - etc.
480 volts.
Two speeds
Draw less current.

11. 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?
Tied together
480 volts.
75 turns.
Circuit Breaker.

12. 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.
An electrical shock hazard may exist.
15 feet off the ground.
Because less current flowing at high voltage causes less line loss per kilowatt.

13. 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
Provides single-phase power to smaller loads such as lights - heaters - etc.
An electromagnet.
3 -979 Volts.

14. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Second-degree burn.
X.
200 volts AC.

15. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Alternating current.
Zero amps.
A grounding resistor.
Current changing constantly in magnitude and periodically in direction.

16. All transformers step voltage up or down by...
75 turns.
Inductance.
A grounding resistor.
12 to 15 times a minute.

17. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
Lower current and higher voltage
Electro-magnetism for their operation.
Cut around clothing that has adhered to the burned area.

18. At what rate should mouth-to-mouth resuscitation be applied?
An electrical shock hazard may exist.
12 to 15 times a minute.
Electro-magnetism for their operation.
75 turns.

19. Current that changes periodically in direction is...
Alternating current.
Full-load - three-phase voltage.
Electro-magnetism for their operation.
The current will read zero.

20. The transformer used only to measure voltage is a...
Zero amps.
Reverse any two-phase leads.
Potential transformer.
Second-degree burn.

21. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Electro-magnetism for their operation.
Four times less than that of the secondary.
Grounded phase and ground fault devices were not operating.
X.

22. To protect against over-current in a three-phase circuit over-current protection must be provided for...
A grounding resistor.
At least two phases
2000 watts
Stator windings.

23. What is the danger when working around capacitors?
Zero amps.
277 volts.
Cut around clothing that has adhered to the burned area.
An electrical shock hazard may exist.

24. The standard frequency of alternating current used at a mine is...
Lower current and higher voltage.
Check to make sure that the victim is not still in contact with the electricity.
Full-load - three-phase voltage.
60 Hertz

25. 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.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Allow for metering voltage and Current.
Derive a neutral for grounding purposes.

26. 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?
Capacitance.
277 volts.
Disconnect the frame-grounding conductor.
150 turns.

27. The size of a transformer is measured in...
Capacitance.
Kilovolt ampere (KVA).
Shunted and taped
Transformer

28. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
Kilovolt ampere (KVA).
Short-circuited after power has been removed.
Continuous.

29. The main function of CT's and PT's on a main substation is to...
200 volts AC.
Allow for metering voltage and Current.
The motor rotation is reversed.
3 -979 Volts.

30. Current in an AC circuit may be measured by...
600 volts.
Shunted and taped
5:1
Clamp-on ammeter.

31. A transformer with a 1:1 ratio is usually a (an)...
100 turns.
200 volts AC.
The motor rotation is reversed.
Isolation transformer.

32. The most reliable method to use to determine whether or not the heart has stopped is by checking the...

33. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
60 cycles per second (60 Hertz).
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
No.6 AWG.
At the source transformer.

34. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Clamp-on ammeter.
Short-circuited after power has been removed.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The sum of the two capacitors.

35. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Lower current and higher voltage
25 feet.
A grounding resistor.
60 Hertz

36. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Derive a neutral for grounding purposes.
Capacitance.
7 -630 volts.
277 volts.

37. Which of the following does a squirrel cage induction motor have?
A.C.
Stator windings.
Full-load - three-phase voltage.
No.6 AWG.

38. 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?
Derive a neutral for grounding purposes.
Provides single-phase power to smaller loads such as lights - heaters - etc.
An electrical shock hazard may exist.
75 turns.

39. When not connected to a load - the secondary leads of a current transformer should be...
H terminals.
A step-up transformer.
Shunted and taped
Transformers.

40. Compared to the secondary of a loaded - step-down transformer - the primary has...
The chest should rise or inflate.
No.6 AWG.
The sum of the two capacitors.
Lower current and higher voltage

41. The primary leads of a single-phase transformer should be connected to the...
H terminals.
Two speeds
25 feet.
Isolation transformer.

42. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Capacitance.
Circuit Breaker.
480 volts.
The chest should rise or inflate.

43. What type motor is a wound-rotor induction motor?
7 -630 volts.
A.C.
Isolation transformer.
5:1

44. Current transformers - or CT's - are used to...
Inductance.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Reverse its rotation.
150 turns.

45. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Larger than that found in the primary winding.
Derive a neutral for grounding purposes.
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.

46. The purpose of a zig-zag transformer is to...
Lower current and higher voltage.
60 cycles per second (60 Hertz).
Derive a neutral for grounding purposes.
A.C.

47. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Squirrel-cage rotor.
600 volts.
75 turns.
The capacitors should be discharged.

48. Where should grounding resistors be located?
800 volts.
Allow for metering voltage and Current.
Reverse any two-phase leads.
At the source transformer.

49. The secondary windings on a 10:1 step-down transformer will have a wire size...
75 turns.
Larger than that found in the primary winding.
Second-degree burn.
They should be made by the same manufacturer.

50. Not true about AC power?
It provides good speed control.
Isolation transformer.
Electro-magnetism for their operation.
150 turns.