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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 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...
7 -630 volts.
Tied together
Clamp-on ammeter.
Shunted and taped

2. Alternating current may be defined as...
Potential transformer.
Current that changes constantly in magnitude and periodically in direction.
Shunted and taped
3 -979 Volts.

3. A transformer with a 1:1 ratio is usually a (an)...
Shunted and taped
A step-up transformer.
Isolation transformer.
Electro-magnetism for their operation.

4. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Inductance.
75 turns.
Short-circuited after power has been removed.
The current will read zero.

5. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Check to make sure that the victim is not still in contact with the electricity.
Tied together
15 feet off the ground.

6. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
Check to make sure that the victim is not still in contact with the electricity.
A step-up transformer.
The current will read zero.

7. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
X.
Capacitance.
A step-up transformer.

8. 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?
Current that changes constantly in magnitude and periodically in direction.
600 volts.
A step-up transformer.
Current changing constantly in magnitude and periodically in direction.

9. 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.
75 turns.
The motor rotation is reversed.
Alternating current.

10. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
Current changing constantly in magnitude and periodically in direction.
2000 watts
No.6 AWG.

11. 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.
Clamp-on ammeter.
A grounding resistor.
5:1
Inductance.

12. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Larger than that found in the primary winding.
Transformer
Grounded phase and ground fault devices were not operating.
2000 watts

13. The transformer used only to measure voltage is a...
60 cycles per second (60 Hertz).
Allow for metering voltage and Current.
Potential transformer.
Continuous.

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

15. The purpose of a zig-zag transformer is to...
Second-degree burn.
100 volts.
Derive a neutral for grounding purposes.
Because less current flowing at high voltage causes less line loss per kilowatt.

16. The main function of CT's and PT's on a main substation is to...
It provides good speed control.
Check to make sure that the victim is not still in contact with the electricity.
Stator windings.
Allow for metering voltage and Current.

17. What steps up or steps down AC voltage?
Draw less current.
277 volts.
75 turns.
Transformer

18. At what rate should mouth-to-mouth resuscitation be applied?
Hyperventilation.
12 to 15 times a minute.
Transformers.
75 turns.

19. The property of an electrical circuit that opposes any change in voltage is called...
1 amp.
480 volts.
Capacitance.
800 volts.

20. AC voltage is raised or lowered by means of...
Two speeds
Transformers.
Electro-magnetism for their operation.
75 turns.

21. If any two-phase wires are reversed on a three-phase motor - the motor will...
Potential transformer.
Reverse any two-phase leads.
Reverse its rotation.
800 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?
60 Hertz
Current changing constantly in magnitude and periodically in direction.
75 turns.
Hyperventilation.

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

24. Where should grounding resistors be located?
At the source transformer.
A.C.
The capacitors should be discharged.
Nearly constant.

25. 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?
3 -979 Volts.
100 turns.
480 volts.
Check to make sure that the victim is not still in contact with the electricity.

26. What is a capacitor?
12 to 15 times a minute.
Capacitance.
A device used to store electrical energy.
They should be made by the same manufacturer.

27. Current transformers - or CT's - are used to...
Capacitance.
5:1.
Transformer
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

28. 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?
H terminals.
75 turns.
The motor rotation is reversed.
Tied together

29. Current that changes periodically in direction is...
Alternating current.
Check to make sure that the victim is not still in contact with the electricity.
Draw less current.
A device used to store electrical energy.

30. The standard frequency of alternating current used at a mine is...
60 cycles per second (60 Hertz).
60 Hertz
The sum of the two capacitors.
Shunted and taped

31. All transformers step voltage up or down by...
Shunted and taped
Inductance.
They must be installed at least 7 feet above the ground.
277 volts.

32. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Disconnect the frame-grounding conductor.
Four times less than that of the secondary.
Lower current and higher voltage.

33. Not true about AC power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The motor rotation is reversed.
Transformers.
It provides good speed control.

34. 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.
H terminals.
277 volts.
Lower current and higher voltage

35. Three-phase AC underground cables must be provided with overcurrent protection using a...
A step-up transformer.
Circuit Breaker.
The capacitors should be discharged.
Clamp-on ammeter.

36. Compared to the secondary of a loaded - step-down transformer - the primary has...
25 feet.
A step-up transformer.
Lower current and higher voltage
Draw less current.

37. The property of an electric circuit that opposes any change in current is called...
Inductance.
Draw less current.
5:1
600 volts.

38. High voltage is used to transmit power over long distances...
800 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
Kilovolt ampere (KVA).
Cut around clothing that has adhered to the burned area.

39. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
1 amp.
X.
Second-degree burn.
Short-circuited after power has been removed.

40. 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?
Circuit Breaker.
200 volts AC.
A step-up transformer.
At least two phases

41. The size of a transformer is measured in...
An electromagnet.
They must be installed at least 7 feet above the ground.
An electrical shock hazard may exist.
Kilovolt ampere (KVA).

42. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Two speeds
Isolation transformer.
A step-up transformer.
75 turns.

43. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Capacitance.
Lower current and higher voltage.
The chest should rise or inflate.
A device used to store electrical energy.

44. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
They should be made by the same manufacturer.
75 turns.
They must be installed at least 7 feet above the ground.
Short-circuited after power has been removed.

45. How do you change the direction of a 3-phase AC motor?
Lower current and higher voltage.
The capacitors should be discharged.
A.C.
Reverse any two-phase leads.

46. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
2000 watts
5:1
Current that changes constantly in magnitude and periodically in direction.
Four times less than that of the secondary.

47. What is the danger when working around capacitors?
An electrical shock hazard may exist.
Tied together
Second-degree burn.
Provides single-phase power to smaller loads such as lights - heaters - etc.

48. 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.
Lower current and higher voltage
Reverse any two-phase leads.
25 feet.
5:1.

49. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
They must be installed at least 7 feet above the ground.
Disconnect the frame-grounding conductor.
Derive a neutral for grounding purposes.

50. A burn causing a blister is classified as a...
Inductance.
Second-degree burn.
X.
1 amp.