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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?
Second-degree burn.
They must be installed at least 7 feet above the ground.
2000 watts
1 amp.

2. Current in an AC circuit may be measured by...
Current that changes constantly in magnitude and periodically in direction.
100 turns.
Electro-magnetism for their operation.
Clamp-on ammeter.

3. Not an acceptable method for the installations of surface transformers?
Four times less than that of the secondary.
The sum of the two capacitors.
They must be installed at least 7 feet above the ground.
The current will read zero.

4. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Because less current flowing at high voltage causes less line loss per kilowatt.
Transformer
H terminals.
They should be made by the same manufacturer.

5. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Draw less current.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Shunted and taped
Draw less current.

6. What should the duty rating of a grounding resistor be?
Carotid pulse - which is located in the neck next to the Adam's apple.
A step-up transformer.
Continuous.
Electro-magnetism for their operation.

7. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Larger than that found in the primary winding.
Short-circuited after power has been removed.
Clamp-on ammeter.
Inductance.

8. What type motor is a wound-rotor induction motor?
Second-degree burn.
Carotid pulse - which is located in the neck next to the Adam's apple.
A.C.
60 Hertz

9. When not connected to a load - the secondary leads of a current transformer should be...
2000 watts
Shunted and taped
5:1
Continuous.

10. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
1 amp.
Provides single-phase power to smaller loads such as lights - heaters - etc.
At least two phases
480 volts.

11. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
100 volts.
Electro-magnetism for their operation.
Zero amps.
Draw less current.

12. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Four times less than that of the secondary.
200 volts AC.
Grounded phase and ground fault devices were not operating.
Cut around clothing that has adhered to the burned area.

13. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Current that changes constantly in magnitude and periodically in direction.
It provides good speed control.
Lower current and higher voltage.

14. A transformer with a 1:1 ratio is usually a (an)...
Current changing constantly in magnitude and periodically in direction.
Disconnect the frame-grounding conductor.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Isolation transformer.

15. At what rate should mouth-to-mouth resuscitation be applied?
An electromagnet.
Derive a neutral for grounding purposes.
12 to 15 times a minute.
15 feet off the ground.

16. The main function of CT's and PT's on a main substation is to...
H terminals.
Lower current and higher voltage.
Allow for metering voltage and Current.
60 Hertz

17. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Larger than that found in the primary winding.
It provides good speed control.
277 volts.

18. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
An electrical shock hazard may exist.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The capacitors should be discharged.

19. 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.
Transformer
The motor rotation is reversed.
Grounded phase and ground fault devices were not operating.

20. 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...
Tied together
Reverse its rotation.
Two speeds
At the source transformer.

21. Which of the following does a squirrel cage induction motor have?
X.
Carotid pulse - which is located in the neck next to the Adam's apple.
Stator windings.
Nearly constant.

22. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Carotid pulse - which is located in the neck next to the Adam's apple.
Reverse any two-phase leads.
The chest should rise or inflate.
60 Hertz

23. The size of a transformer is measured in...
A step-up transformer.
Kilovolt ampere (KVA).
The motor rotation is reversed.
Squirrel-cage induction motor.

24. Three-phase AC underground cables must be provided with overcurrent protection using a...
At least two phases
H terminals.
Circuit Breaker.
Draw less current.

25. A control power transformer...
Squirrel-cage induction motor.
Shunted and taped
2000 watts
Provides single-phase power to smaller loads such as lights - heaters - etc.

26. 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.
Lower current and higher voltage.
Full-load - three-phase voltage.
Allow for metering voltage and Current.

27. The standard frequency of alternating current used at a mine is...
Because less current flowing at high voltage causes less line loss per kilowatt.
60 Hertz
Provides single-phase power to smaller loads such as lights - heaters - etc.
A device used to store electrical energy.

28. What steps up or steps down AC voltage?
Squirrel-cage rotor.
12 to 15 times a minute.
Transformer
60 cycles per second (60 Hertz).

29. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
At least two phases
Larger than that found in the primary winding.
The chest should rise or inflate.

30. Compared to the secondary of a loaded - step-down transformer - the primary has...
Inductance.
2000 watts
Lower current and higher voltage
Hyperventilation.

31. 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.
75 turns.
Electro-magnetism for their operation.
Clamp-on ammeter.

32. 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.
75 turns.
Continuous.
5:1
75 turns.

33. 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.
An electrical shock hazard may exist.
100 turns.
277 volts.

34. Current that changes periodically in direction is...
Isolation transformer.
Full-load - three-phase voltage.
5:1
Alternating current.

35. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Transformers.
At least two phases
Short-circuited after power has been removed.

36. What is the first step to be followed in aiding a victim of electrical shock?
Short-circuited after power has been removed.
2000 watts
Check to make sure that the victim is not still in contact with the electricity.
Disconnect the frame-grounding conductor.

37. The property of an electric circuit that opposes any change in current is called...
Transformers.
Inductance.
The capacitors should be discharged.
Electro-magnetism for their operation.

38. Current transformers - or CT's - are used to...
An electromagnet.
Kilovolt ampere (KVA).
Isolation transformer.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

39. 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.
Shunted and taped
They should be made by the same manufacturer.
5:1.
100 volts.

40. AC voltage is raised or lowered by means of...
3 -979 Volts.
Transformers.
Inductance.
Full-load - three-phase voltage.

41. Not a symptom of electrical shock?.
Second-degree burn.
3 -979 Volts.
Hyperventilation.
The chest should rise or inflate.

42. The primary leads of a single-phase transformer should be connected to the...
Full-load - three-phase voltage.
H terminals.
Draw less current.
Continuous.

43. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
Capacitance.
480 volts.
Cut around clothing that has adhered to the burned area.

44. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Reverse its rotation.
Tied together
No.6 AWG.
An electromagnet.

45. 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.
Disconnect the frame-grounding conductor.
The motor rotation is reversed.
No.6 AWG.

46. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Because less current flowing at high voltage causes less line loss per kilowatt.
Continuous.
75 turns.

47. A burn causing a blister is classified as a...
Stator windings.
Second-degree burn.
Grounded phase and ground fault devices were not operating.
Because less current flowing at high voltage causes less line loss per kilowatt.

48. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Reverse its rotation.
At the source transformer.
At least two phases
7 -630 volts.

49. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
Carotid pulse - which is located in the neck next to the Adam's apple.
800 volts.
Nearly constant.

50. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Capacitance.
A step-up transformer.
5:1
Allow for metering voltage and Current.