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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. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
1 amp.
15 feet off the ground.
Cut around clothing that has adhered to the burned area.
Alternating current.

2. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Two speeds
Full-load - three-phase voltage.
The capacitors should be discharged.
Draw less current.

3. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
600 volts.
Squirrel-cage induction motor.
The capacitors should be discharged.

4. The speed of an alternating current - squirrel-cage induction motor is...
Squirrel-cage rotor.
Nearly constant.
12 to 15 times a minute.
An electrical shock hazard may exist.

5. What steps up or steps down AC voltage?
Cut around clothing that has adhered to the burned area.
Transformer
Alternating current.
Draw less current.

6. High voltage is used to transmit power over long distances...
The sum of the two capacitors.
7 -630 volts.
Squirrel-cage rotor.
Because less current flowing at high voltage causes less line loss per kilowatt.

7. The standard frequency of alternating current used at a mine is...
600 volts.
60 Hertz
Check to make sure that the victim is not still in contact with the electricity.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

8. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Potential transformer.
100 volts.
Capacitance.
2000 watts

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...
Carotid pulse - which is located in the neck next to the Adam's apple.
X.
Tied together
Provides single-phase power to smaller loads such as lights - heaters - etc.

10. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
A step-up transformer.
Grounded phase and ground fault devices were not operating.
1 amp.

11. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Isolation transformer.
25 feet.
2000 watts

12. Three-phase AC underground cables must be provided with overcurrent protection using a...
A device used to store electrical energy.
The chest should rise or inflate.
Draw less current.
Circuit Breaker.

13. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
75 turns.
Because less current flowing at high voltage causes less line loss per kilowatt.
2000 watts

14. 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.
An electromagnet.
Nearly constant.
The chest should rise or inflate.

15. The standard frequency of power supplied by the power company is...
600 volts.
60 cycles per second (60 Hertz).
Shunted and taped
7 -630 volts.

16. Define alternating current...
277 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Current changing constantly in magnitude and periodically in direction.
An electromagnet.

17. What should the duty rating of a grounding resistor be?
Continuous.
75 turns.
At the source transformer.
75 turns.

18. 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.
Carotid pulse - which is located in the neck next to the Adam's apple.
Grounded phase and ground fault devices were not operating.
3 -979 Volts.

19. Not true about AC power?
A step-up transformer.
It provides good speed control.
Draw less current.
12 to 15 times a minute.

20. 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?
It provides good speed control.
12 to 15 times a minute.
The chest should rise or inflate.
100 turns.

21. What is the first step to be followed in aiding a victim of electrical shock?
Check to make sure that the victim is not still in contact with the electricity.
15 feet off the ground.
A device used to store electrical energy.
Alternating current.

22. Current transformers - or CT's - are used to...
480 volts.
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.
25 feet.

23. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
7 -630 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Reverse its rotation.
Electro-magnetism for their operation.

24. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Larger than that found in the primary winding.
A.C.
An electrical shock hazard may exist.

25. Where should grounding resistors be located?
Alternating current.
They must be installed at least 7 feet above the ground.
H terminals.
At the source transformer.

26. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Alternating current.
The capacitors should be discharged.
A device used to store electrical energy.

27. AC voltage is raised or lowered by means of...
No.6 AWG.
Draw less current.
Reverse its rotation.
Transformers.

28. A transformer with a 1:1 ratio is usually a (an)...
60 Hertz
Allow for metering voltage and Current.
A grounding resistor.
Isolation transformer.

29. The purpose of a zig-zag transformer is to...
They should be made by the same manufacturer.
Current changing constantly in magnitude and periodically in direction.
1 amp.
Derive a neutral for grounding purposes.

30. 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.
The sum of the two capacitors.
600 volts.
Transformers.

31. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
5:1.
They should be made by the same manufacturer.
Clamp-on ammeter.

32. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Reverse its rotation.
277 volts.
5:1
Provides single-phase power to smaller loads such as lights - heaters - etc.

33. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
12 to 15 times a minute.
Transformers.
Reverse any two-phase leads.

34. Compared to the secondary of a loaded - step-down transformer - the primary has...
5:1
Full-load - three-phase voltage.
Tied together
Lower current and higher voltage.

35. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Allow for metering voltage and Current.
A grounding resistor.
75 turns.
The current will read zero.

36. What is the danger when working around capacitors?
Current that changes constantly in magnitude and periodically in direction.
Carotid pulse - which is located in the neck next to the Adam's apple.
An electrical shock hazard may exist.
It provides good speed control.

37. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Squirrel-cage rotor.
Full-load - three-phase voltage.
1 amp.
Short-circuited after power has been removed.

38. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Lower current and higher voltage
Four times less than that of the secondary.
A step-up transformer.
At the source transformer.

39. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
200 volts AC.
The motor rotation is reversed.
Electro-magnetism for their operation.
Stator windings.

40. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Provides single-phase power to smaller loads such as lights - heaters - etc.
The chest should rise or inflate.
Hyperventilation.
Because less current flowing at high voltage causes less line loss per kilowatt.

41. 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.
Draw less current.
25 feet.
A.C.
5:1.

42. Which of the following does a squirrel cage induction motor have?
At least two phases
Stator windings.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Capacitance.

43. What is a capacitor?
X.
A grounding resistor.
A device used to store electrical energy.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

44. A control power transformer...
Four times less than that of the secondary.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Nearly constant.

45. The primary leads of a single-phase transformer should be connected to the...
At least two phases
H terminals.
Transformers.
They must be installed at least 7 feet above the ground.

46. 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?
The sum of the two capacitors.
Clamp-on ammeter.
3 -979 Volts.
Tied together

47. The property of an electrical circuit that opposes any change in voltage is called...
800 volts.
3 -979 Volts.
Capacitance.
The capacitors should be discharged.

48. The size of a transformer is measured in...
A step-up transformer.
Short-circuited after power has been removed.
Kilovolt ampere (KVA).
Capacitance.

49. Compared to the secondary of a loaded - step-down transformer - the primary has...
277 volts.
Lower current and higher voltage
Full-load - three-phase voltage.
Shunted and taped

50. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Nearly constant.
25 feet.
No.6 AWG.