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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. 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.
Zero amps.
Kilovolt ampere (KVA).
5:1.

2. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
60 Hertz
277 volts.
Squirrel-cage induction motor.
15 feet off the ground.

3. 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?
Zero amps.
Current changing constantly in magnitude and periodically in direction.
800 volts.
600 volts.

4. At what rate should mouth-to-mouth resuscitation be applied?
Tied together
The current will read zero.
Cut around clothing that has adhered to the burned area.
12 to 15 times a minute.

5. Compared to the secondary of a loaded - step-down transformer - the primary has...
480 volts.
An electrical shock hazard may exist.
Tied together
Lower current and higher voltage.

6. The property of an electrical circuit that opposes any change in voltage is called...
Alternating current.
The motor rotation is reversed.
Lower current and higher voltage.
Capacitance.

7. Where should grounding resistors be located?
They must be installed at least 7 feet above the ground.
Hyperventilation.
480 volts.
At the source transformer.

8. Current transformers - or CT's - are used to...
15 feet off the ground.
Current changing constantly in magnitude and periodically in direction.
An electromagnet.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

9. 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?
200 volts AC.
The chest should rise or inflate.
The current will read zero.
Continuous.

10. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
A grounding resistor.
Short-circuited after power has been removed.
800 volts.
480 volts.

11. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Four times less than that of the secondary.
X.
Continuous.
A device used to store electrical energy.

12. Not an acceptable method for the installations of surface transformers?
15 feet off the ground.
A grounding resistor.
Continuous.
They must be installed at least 7 feet above the ground.

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

14. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Larger than that found in the primary winding.
Draw less current.
7 -630 volts.
At least two phases

15. What is the first step to be followed in aiding a victim of electrical shock?
5:1.
A.C.
277 volts.
Check to make sure that the victim is not still in contact with the electricity.

16. The primary leads of a single-phase transformer should be connected to the...
75 turns.
Inductance.
X.
H terminals.

17. Current in an AC circuit may be measured by...
Allow for metering voltage and Current.
Four times less than that of the secondary.
Clamp-on ammeter.
Larger than that found in the primary winding.

18. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Allow for metering voltage and Current.
Draw less current.
Derive a neutral for grounding purposes.
Two speeds

19. 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...
They must be installed at least 7 feet above the ground.
Larger than that found in the primary winding.
At least two phases
100 volts.

20. The size of a transformer is measured in...
The sum of the two capacitors.
277 volts.
X.
Kilovolt ampere (KVA).

21. 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?
Four times less than that of the secondary.
Transformer
A device used to store electrical energy.
75 turns.

22. 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?
The motor rotation is reversed.
100 turns.
Derive a neutral for grounding purposes.
Grounded phase and ground fault devices were not operating.

23. 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
Zero amps.
Provides single-phase power to smaller loads such as lights - heaters - etc.
An electromagnet.

24. Not a symptom of electrical shock?.
It provides good speed control.
Hyperventilation.
Isolation transformer.
100 volts.

25. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Tied together
They should be made by the same manufacturer.
15 feet off the ground.
600 volts.

26. The standard frequency of alternating current used at a mine is...
Disconnect the frame-grounding conductor.
5:1
60 Hertz
600 volts.

27. The property of an electric circuit that opposes any change in current is called...
15 feet off the ground.
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.
Inductance.

28. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
12 to 15 times a minute.
No.6 AWG.

29. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
At least two phases
Zero amps.
150 turns.

30. The secondary windings on a 10:1 step-down transformer will have a wire size...
Lower current and higher voltage.
Current that changes constantly in magnitude and periodically in direction.
The motor rotation is reversed.
Larger than that found in the primary winding.

31. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Grounded phase and ground fault devices were not operating.
Allow for metering voltage and Current.
Electro-magnetism for their operation.
Disconnect the frame-grounding conductor.

32. All transformers step voltage up or down by...
Inductance.
Grounded phase and ground fault devices were not operating.
Larger than that found in the primary winding.
277 volts.

33. A burn causing a blister is classified as a...
Second-degree burn.
Nearly constant.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
2000 watts

34. Current that changes periodically in direction is...
150 turns.
Alternating current.
Squirrel-cage induction motor.
The chest should rise or inflate.

35. What is the danger when working around capacitors?
100 turns.
The motor rotation is reversed.
A device used to store electrical energy.
An electrical shock hazard may exist.

36. The speed of an alternating current - squirrel-cage induction motor is...
A grounding resistor.
Reverse any two-phase leads.
Nearly constant.
15 feet off the ground.

37. What type of 3-phase AC motor is used most often around a mine?
A step-up transformer.
15 feet off the ground.
Squirrel-cage induction motor.
Two speeds

38. The primary function of a power transformer is to provide...
Zero amps.
H terminals.
75 turns.
Full-load - three-phase voltage.

39. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
An electrical shock hazard may exist.
100 volts.
A step-up transformer.
At least two phases

40. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Reverse its rotation.
No.6 AWG.
800 volts.
The motor rotation is reversed.

41. What type motor is a wound-rotor induction motor?
Hyperventilation.
Transformers.
A.C.
Tied together

42. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Because less current flowing at high voltage causes less line loss per kilowatt.
800 volts.
The current will read zero.
Reverse any two-phase leads.

43. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Electro-magnetism for their operation.
600 volts.
Cut around clothing that has adhered to the burned area.

44. Two 10-hp induction motors are operating on 460 volts AC. One motor is connected by single- phase; the other is connected in three-phase. The three-phase will...
Draw less current.
200 volts AC.
Check to make sure that the victim is not still in contact with the electricity.
5:1.

45. When not connected to a load - the secondary leads of a current transformer should be...
Squirrel-cage rotor.
600 volts.
60 Hertz
Shunted and taped

46. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
Allow for metering voltage and Current.
They should be made by the same manufacturer.
A grounding resistor.

47. Not true about AC power?
It provides good speed control.
Grounded phase and ground fault devices were not operating.
60 cycles per second (60 Hertz).
Because less current flowing at high voltage causes less line loss per kilowatt.

48. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
No.6 AWG.
25 feet.
Circuit Breaker.
277 volts.

49. A transformer with a 1:1 ratio is usually a (an)...
They should be made by the same manufacturer.
Short-circuited after power has been removed.
Isolation transformer.
H terminals.

50. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Grounded phase and ground fault devices were not operating.
600 volts.
Current changing constantly in magnitude and periodically in direction.
2000 watts