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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. 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.
100 volts.
Larger than that found in the primary winding.
5:1
It provides good speed control.

2. The primary leads of a single-phase transformer should be connected to the...
X.
1 amp.
H terminals.
Potential transformer.

3. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Four times less than that of the secondary.
Alternating current.
Two speeds
The current will read zero.

4. 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?
75 turns.
200 volts AC.
Transformers.
Disconnect the frame-grounding conductor.

5. Define alternating current...
At least two phases
Current that changes constantly in magnitude and periodically in direction.
Zero amps.
Current changing constantly in magnitude and periodically in direction.

6. What type of 3-phase AC motor is used most often around a mine?
Kilovolt ampere (KVA).
Squirrel-cage induction motor.
Current changing constantly in magnitude and periodically in direction.
It provides good speed control.

7. The property of an electrical circuit that opposes any change in voltage is called...
An electromagnet.
Lower current and higher voltage
Capacitance.
A step-up transformer.

8. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Derive a neutral for grounding purposes.
480 volts.
Short-circuited after power has been removed.
Reverse any two-phase leads.

9. The size of a transformer is measured in...
At least two phases
Kilovolt ampere (KVA).
Hyperventilation.
Circuit Breaker.

10. 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?
Transformers.
An electromagnet.
At least two phases
75 turns.

11. The transformer used only to measure voltage is a...
They must be installed at least 7 feet above the ground.
Two speeds
Potential transformer.
An electrical shock hazard may exist.

12. The secondary windings on a 10:1 step-down transformer will have a wire size...
100 turns.
1 amp.
Squirrel-cage induction motor.
Larger than that found in the primary winding.

13. The purpose of a zig-zag transformer is to...
100 volts.
Capacitance.
Derive a neutral for grounding purposes.
Continuous.

14. Current transformers - or CT's - are used to...
Transformer
Allow for metering voltage and Current.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
They must be installed at least 7 feet above the ground.

15. Alternating current may be defined as...
Lower current and higher voltage.
Current that changes constantly in magnitude and periodically in direction.
100 volts.
15 feet off the ground.

16. A solenoid coil is...
200 volts AC.
The sum of the two capacitors.
An electromagnet.
Inductance.

17. 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...
A device used to store electrical energy.
A step-up transformer.
100 volts.
At least two phases

18. A control power transformer...
Shunted and taped
Reverse any two-phase leads.
Potential transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.

19. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
Current changing constantly in magnitude and periodically in direction.
Alternating current.
Carotid pulse - which is located in the neck next to the Adam's apple.

20. The property of an electric circuit that opposes any change in current is called...
Clamp-on ammeter.
7 -630 volts.
277 volts.
Inductance.

21. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Draw less current.
A step-up transformer.
Current changing constantly in magnitude and periodically in direction.
7 -630 volts.

22. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Isolation transformer.
The motor rotation is reversed.
Clamp-on ammeter.
Allow for metering voltage and Current.

23. At what rate should mouth-to-mouth resuscitation be applied?
Check to make sure that the victim is not still in contact with the electricity.
12 to 15 times a minute.
An electrical shock hazard may exist.
Squirrel-cage rotor.

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

25. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
The capacitors should be discharged.
15 feet off the ground.
75 turns.

26. 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 volts.
Short-circuited after power has been removed.
The current will read zero.
100 turns.

27. Compared to the secondary of a loaded - step-down transformer - the primary has...
Hyperventilation.
The motor rotation is reversed.
Lower current and higher voltage
They must be installed at least 7 feet above the ground.

28. 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...
3 -979 Volts.
Draw less current.
Allow for metering voltage and Current.
It provides good speed control.

29. What type motor is a wound-rotor induction motor?
Clamp-on ammeter.
A.C.
1 amp.
Transformer

30. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Draw less current.
Lower current and higher voltage.
Check to make sure that the victim is not still in contact with the electricity.
X.

31. What steps up or steps down AC voltage?
Transformer
Capacitance.
Clamp-on ammeter.
Kilovolt ampere (KVA).

32. Not true about AC power?
An electromagnet.
It provides good speed control.
Full-load - three-phase voltage.
100 turns.

33. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Second-degree burn.
5:1
Four times less than that of the secondary.
It provides good speed control.

34. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Allow for metering voltage and Current.
5:1.
2000 watts
Current that changes constantly in magnitude and periodically in direction.

35. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
A grounding resistor.
They should be made by the same manufacturer.
12 to 15 times a minute.
800 volts.

36. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
25 feet.
1 amp.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
A device used to store electrical energy.

37. 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?
600 volts.
Nearly constant.
Lower current and higher voltage
150 turns.

38. Operating coils - motors - transformers - relays and solenoids depend upon...
Circuit Breaker.
They should be made by the same manufacturer.
Carotid pulse - which is located in the neck next to the Adam's apple.
Electro-magnetism for their operation.

39. What should the duty rating of a grounding resistor be?
75 turns.
Continuous.
Nearly constant.
12 to 15 times a minute.

40. AC voltage is raised or lowered by means of...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
A.C.
Potential transformer.
Transformers.

41. Compared to the secondary of a loaded - step-down transformer - the primary has...
They should be made by the same manufacturer.
They must be installed at least 7 feet above the ground.
Inductance.
Lower current and higher voltage.

42. A transformer with a 1:1 ratio is usually a (an)...
Allow for metering voltage and Current.
Isolation transformer.
The capacitors should be discharged.
Squirrel-cage rotor.

43. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
800 volts.
Short-circuited after power has been removed.
The chest should rise or inflate.
Provides single-phase power to smaller loads such as lights - heaters - etc.

44. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
H terminals.
Inductance.
Draw less current.

45. Three-phase AC underground cables must be provided with overcurrent protection using a...
A grounding resistor.
An electromagnet.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Circuit Breaker.

46. 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?
The motor rotation is reversed.
Lower current and higher voltage.
Zero amps.
800 volts.

47. How should clothing be removed from a burn?
Circuit Breaker.
480 volts.
Cut around clothing that has adhered to the burned area.
Allow for metering voltage and Current.

48. Which of the following does a squirrel cage induction motor have?
Derive a neutral for grounding purposes.
600 volts.
Stator windings.
Continuous.

49. Current in an AC circuit may be measured by...
Reverse its rotation.
Potential transformer.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Clamp-on ammeter.

50. What is the danger when working around capacitors?
Squirrel-cage rotor.
Stator windings.
A device used to store electrical energy.
An electrical shock hazard may exist.