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

2. Not an acceptable method for the installations of surface transformers?
800 volts.
Cut around clothing that has adhered to the burned area.
Current that changes constantly in magnitude and periodically in direction.
They must be installed at least 7 feet above the ground.

3. What should the duty rating of a grounding resistor be?
Reverse any two-phase leads.
At least two phases
Continuous.
Short-circuited after power has been removed.

4. When not connected to a load - the secondary leads of a current transformer should be...
They must be installed at least 7 feet above the ground.
The current will read zero.
Shunted and taped
Inductance.

5. The speed of an alternating current - squirrel-cage induction motor is...
Draw less current.
200 volts AC.
Grounded phase and ground fault devices were not operating.
Nearly constant.

6. 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.
5:1
Four times less than that of the secondary.
Two speeds

7. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
Because less current flowing at high voltage causes less line loss per kilowatt.
Full-load - three-phase voltage.
At least two phases

8. 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?
Draw less current.
480 volts.
The sum of the two capacitors.
75 turns.

9. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
The motor rotation is reversed.
Potential transformer.
Inductance.

10. The main function of CT's and PT's on a main substation is to...
At least two phases
Derive a neutral for grounding purposes.
Allow for metering voltage and Current.
Zero amps.

11. The standard frequency of power supplied by the power company is...
200 volts AC.
60 cycles per second (60 Hertz).
Isolation transformer.
Stator windings.

12. The standard frequency of alternating current used at a mine is...
It provides good speed control.
600 volts.
60 Hertz
Draw less current.

13. A solenoid coil is...
75 turns.
Disconnect the frame-grounding conductor.
An electromagnet.
No.6 AWG.

14. Current that changes periodically in direction is...
Nearly constant.
Shunted and taped
The chest should rise or inflate.
Alternating current.

15. 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.
Squirrel-cage rotor.
5:1.
Lower current and higher voltage
Shunted and taped

16. How should clothing be removed from a burn?
Squirrel-cage induction motor.
A step-up transformer.
Cut around clothing that has adhered to the burned area.
Short-circuited after power has been removed.

17. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Tied together
75 turns.
A grounding resistor.

18. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
Transformer
Kilovolt ampere (KVA).
Second-degree burn.

19. What is the danger when working around capacitors?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Shunted and taped
An electrical shock hazard may exist.
2000 watts

20. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
7 -630 volts.
A grounding resistor.
Kilovolt ampere (KVA).
Tied together

21. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
The chest should rise or inflate.
They should be made by the same manufacturer.
480 volts.
3 -979 Volts.

22. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Inductance.
Cut around clothing that has adhered to the burned area.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
25 feet.

23. 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?
Carotid pulse - which is located in the neck next to the Adam's apple.
75 turns.
200 volts AC.
Squirrel-cage rotor.

24. The primary function of a power transformer is to provide...
60 cycles per second (60 Hertz).
Full-load - three-phase voltage.
Shunted and taped
An electromagnet.

25. Alternating current may be defined as...
Cut around clothing that has adhered to the burned area.
150 turns.
Four times less than that of the secondary.
Current that changes constantly in magnitude and periodically in direction.

26. AC voltage is raised or lowered by means of...
Inductance.
Derive a neutral for grounding purposes.
Transformers.
At the source transformer.

27. The combined capacitance of two capacitors in parallel is...
75 turns.
The sum of the two capacitors.
Stator windings.
Kilovolt ampere (KVA).

28. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
Capacitance.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
12 to 15 times a minute.

29. What position of a selector switch using a voltmeter would you select to check a 120-volt AC circuit to obtain the most accurate reading?
X.
Check to make sure that the victim is not still in contact with the electricity.
800 volts.
200 volts AC.

30. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Potential transformer.
A step-up transformer.
Stator windings.
Short-circuited after power has been removed.

31. Not a symptom of electrical shock?.
Because less current flowing at high voltage causes less line loss per kilowatt.
Lower current and higher voltage.
Hyperventilation.
Draw less current.

32. A burn causing a blister is classified as a...
Grounded phase and ground fault devices were not operating.
Clamp-on ammeter.
The current will read zero.
Second-degree burn.

33. A wound-rotor induction motor has all the following EXCEPT...
Lower current and higher voltage
Electro-magnetism for their operation.
800 volts.
Squirrel-cage rotor.

34. Compared to the secondary of a loaded - step-down transformer - the primary has...
Draw less current.
Derive a neutral for grounding purposes.
Lower current and higher voltage
Isolation transformer.

35. Current transformers - or CT's - are used to...
Continuous.
Current that changes constantly in magnitude and periodically in direction.
Tied together
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

36. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
The motor rotation is reversed.
2000 watts
75 turns.
Tied together

37. If any two-phase wires are reversed on a three-phase motor - the motor will...
Short-circuited after power has been removed.
200 volts AC.
Reverse its rotation.
Stator windings.

38. 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?
Squirrel-cage induction motor.
Draw less current.
3 -979 Volts.
Reverse any two-phase leads.

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

40. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Reverse its rotation.
Draw less current.
15 feet off the ground.
100 volts.

41. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
A.C.
Lower current and higher voltage
The motor rotation is reversed.

42. 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?
Potential transformer.
They should be made by the same manufacturer.
X.
600 volts.

43. How do you change the direction of a 3-phase AC motor?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Capacitance.
12 to 15 times a minute.
Reverse any two-phase leads.

44. Which of the following does a squirrel cage induction motor have?
It provides good speed control.
Stator windings.
Short-circuited after power has been removed.
Squirrel-cage induction motor.

45. Not true about AC power?
1 amp.
It provides good speed control.
150 turns.
Stator windings.

46. The transformer used only to measure voltage is a...
An electromagnet.
Transformer
Current that changes constantly in magnitude and periodically in direction.
Potential transformer.

47. Three-phase AC underground cables must be provided with overcurrent protection using a...
Clamp-on ammeter.
Circuit Breaker.
Lower current and higher voltage
Alternating current.

48. 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.
277 volts.
Lower current and higher voltage.
Zero amps.

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.
Check to make sure that the victim is not still in contact with the electricity.
7 -630 volts.
Disconnect the frame-grounding conductor.

50. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A grounding resistor.
Tied together
Potential transformer.
A.C.