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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. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
Reverse any two-phase leads.
15 feet off the ground.
Isolation transformer.

2. How should clothing be removed from a burn?
Continuous.
Cut around clothing that has adhered to the burned area.
Second-degree burn.
Short-circuited after power has been removed.

3. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
100 turns.
Reverse any two-phase leads.
The chest should rise or inflate.
Lower current and higher voltage

4. 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.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Two speeds
277 volts.

5. The property of an electric circuit that opposes any change in current is called...
H terminals.
Circuit Breaker.
Inductance.
60 cycles per second (60 Hertz).

6. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Draw less current.
Zero amps.
100 volts.
The current will read zero.

7. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
A grounding resistor.
An electrical shock hazard may exist.
An electromagnet.

8. Compared to the secondary of a loaded - step-down transformer - the primary has...
A device used to store electrical energy.
Lower current and higher voltage.
Larger than that found in the primary winding.
15 feet off the ground.

9. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
The motor rotation is reversed.
Two speeds
Because less current flowing at high voltage causes less line loss per kilowatt.

10. What should the duty rating of a grounding resistor be?
Continuous.
A.C.
Shunted and taped
800 volts.

11. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
75 turns.
Second-degree burn.
60 cycles per second (60 Hertz).

12. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Because less current flowing at high voltage causes less line loss per kilowatt.
Disconnect the frame-grounding conductor.
Squirrel-cage rotor.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

13. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
They must be installed at least 7 feet above the ground.
The current will read zero.
H terminals.
75 turns.

14. How do you change the direction of a 3-phase AC motor?
277 volts.
Reverse any two-phase leads.
Continuous.
100 volts.

15. 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.
12 to 15 times a minute.
5:1
Derive a neutral for grounding purposes.

16. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Hyperventilation.
Zero amps.
277 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

17. AC voltage is raised or lowered by means of...
Carotid pulse - which is located in the neck next to the Adam's apple.
The sum of the two capacitors.
At the source transformer.
Transformers.

18. When not connected to a load - the secondary leads of a current transformer should be...
Transformer
12 to 15 times a minute.
600 volts.
Shunted and taped

19. The speed of an alternating current - squirrel-cage induction motor is...
At the source transformer.
An electrical shock hazard may exist.
At least two phases
Nearly constant.

20. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Full-load - three-phase voltage.
A grounding resistor.
Provides single-phase power to smaller loads such as lights - heaters - etc.
100 volts.

21. At what rate should mouth-to-mouth resuscitation be applied?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
An electromagnet.
12 to 15 times a minute.
100 volts.

22. 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?
75 turns.
Full-load - three-phase voltage.
2000 watts
A device used to store electrical energy.

23. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
Current changing constantly in magnitude and periodically in direction.
480 volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.

24. Current in an AC circuit may be measured by...
Inductance.
Because less current flowing at high voltage causes less line loss per kilowatt.
Clamp-on ammeter.
Circuit Breaker.

25. 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...
60 Hertz
An electrical shock hazard may exist.
Tied together
Capacitance.

26. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Cut around clothing that has adhered to the burned area.
The capacitors should be discharged.
Isolation transformer.

27. Not a symptom of electrical shock?.
Electro-magnetism for their operation.
Larger than that found in the primary winding.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Hyperventilation.

28. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Inductance.
Grounded phase and ground fault devices were not operating.
Shunted and taped
60 cycles per second (60 Hertz).

29. 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...
100 volts.
Draw less current.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Squirrel-cage rotor.

30. A burn causing a blister is classified as a...
A grounding resistor.
Second-degree burn.
Disconnect the frame-grounding conductor.
7 -630 volts.

31. 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.
Transformer
5:1
Reverse any two-phase leads.
Inductance.

32. Which of the following does a squirrel cage induction motor have?
Continuous.
The sum of the two capacitors.
The chest should rise or inflate.
Stator windings.

33. The main function of CT's and PT's on a main substation is to...
Transformer
Allow for metering voltage and Current.
Lower current and higher voltage.
Nearly constant.

34. What is the danger when working around capacitors?
Nearly constant.
A.C.
An electrical shock hazard may exist.
Zero amps.

35. The standard frequency of alternating current used at a mine is...
Larger than that found in the primary winding.
Because less current flowing at high voltage causes less line loss per kilowatt.
3 -979 Volts.
60 Hertz

36. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Zero amps.
The capacitors should be discharged.
No.6 AWG.
75 turns.

37. To protect against over-current in a three-phase circuit over-current protection must be provided for...
25 feet.
Carotid pulse - which is located in the neck next to the Adam's apple.
At the source transformer.
At least two phases

38. What is a capacitor?
The motor rotation is reversed.
A device used to store electrical energy.
A grounding resistor.
Circuit Breaker.

39. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The sum of the two capacitors.
The motor rotation is reversed.
A step-up transformer.
X.

40. What steps up or steps down AC voltage?
Lower current and higher voltage.
Transformer
Draw less current.
Cut around clothing that has adhered to the burned area.

41. 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.
At least two phases
1 amp.
It provides good speed control.

42. Where should grounding resistors be located?
25 feet.
At the source transformer.
Larger than that found in the primary winding.
60 cycles per second (60 Hertz).

43. The transformer used only to measure voltage is a...
Isolation transformer.
480 volts.
Potential transformer.
Derive a neutral for grounding purposes.

44. All transformers step voltage up or down by...
The sum of the two capacitors.
Inductance.
60 cycles per second (60 Hertz).
Nearly constant.

45. 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?
5:1.
Stator windings.
150 turns.
Zero amps.

46. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Grounded phase and ground fault devices were not operating.
Lower current and higher voltage
Isolation transformer.

47. 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?
600 volts.
A.C.
277 volts.
Two speeds

48. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
Electro-magnetism for their operation.
Current that changes constantly in magnitude and periodically in direction.
200 volts AC.

49. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Potential transformer.
Electro-magnetism for their operation.
Two speeds
Grounded phase and ground fault devices were not operating.

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