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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 current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
An electrical shock hazard may exist.
1 amp.
X.
Shunted and taped

2. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
X.
3 -979 Volts.
100 volts.
277 volts.

3. The primary leads of a single-phase transformer should be connected to the...
They must be installed at least 7 feet above the ground.
Squirrel-cage rotor.
5:1.
H terminals.

4. Not an acceptable method for the installations of surface transformers?
Draw less current.
They must be installed at least 7 feet above the ground.
Full-load - three-phase voltage.
Check to make sure that the victim is not still in contact with the electricity.

5. Current that changes periodically in direction is...
A grounding resistor.
5:1.
Alternating current.
Inductance.

6. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
A device used to store electrical energy.
60 cycles per second (60 Hertz).
Current that changes constantly in magnitude and periodically in direction.
Four times less than that of the secondary.

7. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
Cut around clothing that has adhered to the burned area.
Larger than that found in the primary winding.
Because less current flowing at high voltage causes less line loss per kilowatt.

8. What should the duty rating of a grounding resistor be?
The capacitors should be discharged.
12 to 15 times a minute.
Kilovolt ampere (KVA).
Continuous.

9. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Grounded phase and ground fault devices were not operating.
Stator windings.
Disconnect the frame-grounding conductor.
Squirrel-cage rotor.

10. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
25 feet.
60 cycles per second (60 Hertz).
A grounding resistor.
The current will read zero.

11. What type motor is a wound-rotor induction motor?
A.C.
Clamp-on ammeter.
3 -979 Volts.
Allow for metering voltage and Current.

12. A transformer with a 1:1 ratio is usually a (an)...
The capacitors should be discharged.
Isolation transformer.
Derive a neutral for grounding purposes.
5:1.

13. The standard frequency of alternating current used at a mine is...
480 volts.
Reverse any two-phase leads.
60 Hertz
Squirrel-cage rotor.

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...
The motor rotation is reversed.
At least two phases
Isolation transformer.
100 volts.

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

16. Current transformers - or CT's - are used to...
15 feet off the ground.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Kilovolt ampere (KVA).
An electromagnet.

17. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Carotid pulse - which is located in the neck next to the Adam's apple.
100 turns.
No.6 AWG.
5:1.

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?
7 -630 volts.
Hyperventilation.
Potential transformer.
75 turns.

19. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
X.
12 to 15 times a minute.
60 cycles per second (60 Hertz).

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?
100 turns.
A step-up transformer.
At least two phases
277 volts.

21. The combined capacitance of two capacitors in parallel is...
Full-load - three-phase voltage.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The sum of the two capacitors.
200 volts AC.

22. All transformers step voltage up or down by...
Two speeds
Draw less current.
They should be made by the same manufacturer.
Inductance.

23. What steps up or steps down AC voltage?
15 feet off the ground.
Transformer
Inductance.
Disconnect the frame-grounding conductor.

24. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
Lower current and higher voltage.
Two speeds
Current changing constantly in magnitude and periodically in direction.

25. The purpose of a zig-zag transformer is to...
Potential transformer.
Inductance.
800 volts.
Derive a neutral for grounding purposes.

26. The main function of CT's and PT's on a main substation is to...
Check to make sure that the victim is not still in contact with the electricity.
Allow for metering voltage and Current.
Four times less than that of the secondary.
Grounded phase and ground fault devices were not operating.

27. Where should grounding resistors be located?
15 feet off the ground.
Draw less current.
12 to 15 times a minute.
At the source transformer.

28. The primary function of a power transformer is to provide...
800 volts.
Full-load - three-phase voltage.
277 volts.
150 turns.

29. To protect against over-current in a three-phase circuit over-current protection must be provided for...
An electromagnet.
Alternating current.
Lower current and higher voltage
At least two phases

30. 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?
A grounding resistor.
75 turns.
Shunted and taped
150 turns.

31. Not a symptom of electrical shock?.
No.6 AWG.
Hyperventilation.
60 cycles per second (60 Hertz).
60 Hertz

32. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
480 volts.
Grounded phase and ground fault devices were not operating.
Because less current flowing at high voltage causes less line loss per kilowatt.

33. Current in an AC circuit may be measured by...
Clamp-on ammeter.
No.6 AWG.
Squirrel-cage rotor.
Carotid pulse - which is located in the neck next to the Adam's apple.

34. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
An electromagnet.
A.C.
Derive a neutral for grounding purposes.

35. 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?
Second-degree burn.
Stator windings.
Full-load - three-phase voltage.
150 turns.

36. 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?
800 volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Lower current and higher voltage
Reverse its rotation.

37. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Stator windings.
Circuit Breaker.
Alternating current.

38. The size of a transformer is measured in...
Squirrel-cage induction motor.
Tied together
Current that changes constantly in magnitude and periodically in direction.
Kilovolt ampere (KVA).

39. What is the danger when working around capacitors?
75 turns.
At the source transformer.
Alternating current.
An electrical shock hazard may exist.

40. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
2000 watts
75 turns.
Full-load - three-phase voltage.

41. 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?
At least two phases
200 volts AC.
Short-circuited after power has been removed.
2000 watts

42. The secondary windings on a 10:1 step-down transformer will have a wire size...
Two speeds
150 turns.
Larger than that found in the primary winding.
Squirrel-cage rotor.

43. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
3 -979 Volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
Cut around clothing that has adhered to the burned area.
Two speeds

44. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
The motor rotation is reversed.
Grounded phase and ground fault devices were not operating.
Transformers.

45. What is a capacitor?
Second-degree burn.
A device used to store electrical energy.
75 turns.
25 feet.

46. Three-phase AC underground cables must be provided with overcurrent protection using a...
277 volts.
Circuit Breaker.
200 volts AC.
Alternating current.

47. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Shunted and taped
The chest should rise or inflate.
Zero amps.
Inductance.

48. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
Transformers.
1 amp.
Two speeds

49. Not true about AC power?
Grounded phase and ground fault devices were not operating.
Transformers.
Larger than that found in the primary winding.
It provides good speed control.

50. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
15 feet off the ground.
Capacitance.
The chest should rise or inflate.