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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. 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...
At the source transformer.
Draw less current.
5:1
Nearly constant.

2. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
200 volts AC.
X.
Squirrel-cage rotor.
600 volts.

3. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Four times less than that of the secondary.
The motor rotation is reversed.
150 turns.
5:1

4. The secondary windings on a 10:1 step-down transformer will have a wire size...
12 to 15 times a minute.
A device used to store electrical energy.
Larger than that found in the primary winding.
An electromagnet.

5. The standard frequency of alternating current used at a mine is...
At least two phases
60 Hertz
60 cycles per second (60 Hertz).
Lower current and higher voltage.

6. How do you change the direction of a 3-phase AC motor?
2000 watts
7 -630 volts.
Reverse any two-phase leads.
No.6 AWG.

7. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Current changing constantly in magnitude and periodically in direction.
They should be made by the same manufacturer.
A step-up transformer.
800 volts.

8. Not a symptom of electrical shock?.
They should be made by the same manufacturer.
Inductance.
Hyperventilation.
Cut around clothing that has adhered to the burned area.

9. 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?
At least two phases
Draw less current.
600 volts.
150 turns.

10. A solenoid coil is...
H terminals.
Two speeds
An electromagnet.
480 volts.

11. Not an acceptable method for the installations of surface transformers?
Clamp-on ammeter.
Draw less current.
They must be installed at least 7 feet above the ground.
5:1

12. A wound-rotor induction motor has all the following EXCEPT...
X.
Squirrel-cage rotor.
60 cycles per second (60 Hertz).
At least two phases

13. Define alternating current...
Full-load - three-phase voltage.
The motor rotation is reversed.
5:1
Current changing constantly in magnitude and periodically in direction.

14. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Draw less current.
Two speeds
Inductance.
An electromagnet.

15. 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...
1 amp.
At the source transformer.
100 volts.
Shunted and taped

16. 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.
They should be made by the same manufacturer.
Inductance.
At least two phases

17. A transformer with a 1:1 ratio is usually a (an)...
Larger than that found in the primary winding.
Nearly constant.
Isolation transformer.
X.

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

19. Current in an AC circuit may be measured by...
Draw less current.
100 volts.
At the source transformer.
Clamp-on ammeter.

20. 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?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
A.C.
200 volts AC.
75 turns.

21. The primary function of a power transformer is to provide...
Second-degree burn.
A device used to store electrical energy.
Allow for metering voltage and Current.
Full-load - three-phase voltage.

22. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Full-load - three-phase voltage.
A.C.
Capacitance.

23. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
277 volts.
75 turns.
H terminals.

24. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Full-load - three-phase voltage.
The current will read zero.
25 feet.
100 volts.

25. At what rate should mouth-to-mouth resuscitation be applied?
Isolation transformer.
12 to 15 times a minute.
Full-load - three-phase voltage.
480 volts.

26. What is the first step to be followed in aiding a victim of electrical shock?
800 volts.
Draw less current.
Check to make sure that the victim is not still in contact with the electricity.
Grounded phase and ground fault devices were not operating.

27. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Capacitance.
Two speeds
Disconnect the frame-grounding conductor.
25 feet.

28. The property of an electric circuit that opposes any change in current is called...
Transformer
Circuit Breaker.
Inductance.
Full-load - three-phase voltage.

29. How should clothing be removed from a burn?
They should be made by the same manufacturer.
Cut around clothing that has adhered to the burned area.
The sum of the two capacitors.
Inductance.

30. What type motor is a wound-rotor induction motor?
Isolation transformer.
Inductance.
A.C.
Disconnect the frame-grounding conductor.

31. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
277 volts.
12 to 15 times a minute.
3 -979 Volts.
Tied together

32. Compared to the secondary of a loaded - step-down transformer - the primary has...
12 to 15 times a minute.
Lower current and higher voltage
X.
Electro-magnetism for their operation.

33. What is a capacitor?
Alternating current.
Zero amps.
A device used to store electrical energy.
480 volts.

34. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
The chest should rise or inflate.
Two speeds
Lower current and higher voltage.
Zero amps.

35. Which of the following does a squirrel cage induction motor have?
Stator windings.
Shunted and taped
Potential transformer.
Four times less than that of the secondary.

36. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Reverse its rotation.
The chest should rise or inflate.
Zero amps.
2000 watts

37. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
A step-up transformer.
At the source transformer.
A.C.

38. High voltage is used to transmit power over long distances...
No.6 AWG.
Because less current flowing at high voltage causes less line loss per kilowatt.
Current changing constantly in magnitude and periodically in direction.
They must be installed at least 7 feet above the ground.

39. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Larger than that found in the primary winding.
The current will read zero.
Check to make sure that the victim is not still in contact with the electricity.
At least two phases

40. Where should grounding resistors be located?
Stator windings.
A.C.
At the source transformer.
An electrical shock hazard may exist.

41. 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?
3 -979 Volts.
The motor rotation is reversed.
480 volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.

42. 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?
They should be made by the same manufacturer.
3 -979 Volts.
A device used to store electrical energy.
100 turns.

43. 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?
75 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.
60 cycles per second (60 Hertz).
H terminals.

44. Current transformers - or CT's - are used to...
Larger than that found in the primary winding.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Kilovolt ampere (KVA).
The sum of the two capacitors.

45. 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.
The chest should rise or inflate.
At the source transformer.
The current will read zero.

46. A burn causing a blister is classified as a...
Carotid pulse - which is located in the neck next to the Adam's apple.
Lower current and higher voltage
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Second-degree burn.

47. 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.
Tied together
5:1.
At the source transformer.
The sum of the two capacitors.

48. 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?
25 feet.
75 turns.
100 turns.
800 volts.

49. 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 cycles per second (60 Hertz).
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
25 feet.
Tied together

50. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Transformers.
Tied together
H terminals.