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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 current on the primary side of a step-down transformer with a 4:1 ratio will be...
The motor rotation is reversed.
150 turns.
5:1
Four times less than that of the secondary.

2. Current transformers - or CT's - are used to...
The capacitors should be discharged.
Second-degree burn.
60 cycles per second (60 Hertz).
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

3. 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?
Squirrel-cage induction motor.
800 volts.
Continuous.
Clamp-on ammeter.

4. 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...
A.C.
Potential transformer.
Draw less current.
Squirrel-cage induction motor.

5. If any two-phase wires are reversed on a three-phase motor - the motor will...
Electro-magnetism for their operation.
The chest should rise or inflate.
Inductance.
Reverse its rotation.

6. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Continuous.
25 feet.
Disconnect the frame-grounding conductor.
Full-load - three-phase voltage.

7. AC voltage is raised or lowered by means of...
Lower current and higher voltage.
Transformer
A grounding resistor.
Transformers.

8. What is the danger when working around capacitors?
Current that changes constantly in magnitude and periodically in direction.
The capacitors should be discharged.
Potential transformer.
An electrical shock hazard may exist.

9. The purpose of a zig-zag transformer is to...
15 feet off the ground.
Zero amps.
Derive a neutral for grounding purposes.
It provides good speed control.

10. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
A grounding resistor.
X.
Squirrel-cage induction motor.
Cut around clothing that has adhered to the burned area.

11. What steps up or steps down AC voltage?
No.6 AWG.
480 volts.
The chest should rise or inflate.
Transformer

12. 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?
A step-up transformer.
Squirrel-cage rotor.
Inductance.
75 turns.

13. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
It provides good speed control.
The capacitors should be discharged.
Draw less current.
5:1

14. A burn causing a blister is classified as a...
X.
5:1
Potential transformer.
Second-degree burn.

15. The main function of CT's and PT's on a main substation is to...
800 volts.
Nearly constant.
15 feet off the ground.
Allow for metering voltage and Current.

16. 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?
800 volts.
No.6 AWG.
3 -979 Volts.
Short-circuited after power has been removed.

17. The primary function of a power transformer is to provide...
Larger than that found in the primary winding.
Transformer
Full-load - three-phase voltage.
Cut around clothing that has adhered to the burned area.

18. The standard frequency of power supplied by the power company is...
No.6 AWG.
60 cycles per second (60 Hertz).
Derive a neutral for grounding purposes.
It provides good speed control.

19. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Potential transformer.
A grounding resistor.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Transformers.

20. Alternating current may be defined as...
Disconnect the frame-grounding conductor.
Current that changes constantly in magnitude and periodically in direction.
Capacitance.
Shunted and taped

21. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Reverse its rotation.
Current that changes constantly in magnitude and periodically in direction.
2000 watts

22. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
A.C.
Short-circuited after power has been removed.
They should be made by the same manufacturer.
Hyperventilation.

23. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
Stator windings.
Isolation transformer.
A grounding resistor.

24. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
150 turns.
5:1.
Zero amps.
A step-up transformer.

25. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Hyperventilation.
Potential transformer.
Derive a neutral for grounding purposes.

26. At what rate should mouth-to-mouth resuscitation be applied?
Current that changes constantly in magnitude and periodically in direction.
12 to 15 times a minute.
An electromagnet.
The current will read zero.

27. What should the duty rating of a grounding resistor be?
Continuous.
60 cycles per second (60 Hertz).
Clamp-on ammeter.
Electro-magnetism for their operation.

28. Compared to the secondary of a loaded - step-down transformer - the primary has...
Larger than that found in the primary winding.
Lower current and higher voltage.
At least two phases
150 turns.

29. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Short-circuited after power has been removed.
Allow for metering voltage and Current.
The current will read zero.
200 volts AC.

30. 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.
An electromagnet.
Lower current and higher voltage.
Inductance.

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

32. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
The sum of the two capacitors.
2000 watts
An electrical shock hazard may exist.
60 cycles per second (60 Hertz).

33. A solenoid coil is...
An electromagnet.
Reverse its rotation.
It provides good speed control.
277 volts.

34. How should clothing be removed from a burn?
Check to make sure that the victim is not still in contact with the electricity.
Draw less current.
60 cycles per second (60 Hertz).
Cut around clothing that has adhered to the burned area.

35. Current in an AC circuit may be measured by...
Clamp-on ammeter.
The chest should rise or inflate.
Capacitance.
Lower current and higher voltage.

36. 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.
Isolation transformer.
Reverse any two-phase leads.
Larger than that found in the primary winding.
5:1

37. The transformer used only to measure voltage is a...
15 feet off the ground.
The chest should rise or inflate.
Potential transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.

38. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
75 turns.
25 feet.
Short-circuited after power has been removed.

39. Three-phase AC underground cables must be provided with overcurrent protection using a...
3 -979 Volts.
Circuit Breaker.
Continuous.
800 volts.

40. The property of an electrical circuit that opposes any change in voltage is called...
Squirrel-cage induction motor.
Capacitance.
The chest should rise or inflate.
5:1

41. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
60 cycles per second (60 Hertz).
100 turns.
An electromagnet.

42. The secondary windings on a 10:1 step-down transformer will have a wire size...
60 Hertz
Derive a neutral for grounding purposes.
Larger than that found in the primary winding.
Lower current and higher voltage.

43. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Grounded phase and ground fault devices were not operating.
Squirrel-cage rotor.
2000 watts
Lower current and higher voltage.

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

45. 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.
X.
Alternating current.
2000 watts
5:1.

46. What is the first step to be followed in aiding a victim of electrical shock?
3 -979 Volts.
Short-circuited after power has been removed.
Check to make sure that the victim is not still in contact with the electricity.
Inductance.

47. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
The sum of the two capacitors.
60 Hertz
Short-circuited after power has been removed.
They should be made by the same manufacturer.

48. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Second-degree burn.
Capacitance.

49. Which of the following does a squirrel cage induction motor have?
Current changing constantly in magnitude and periodically in direction.
3 -979 Volts.
Stator windings.
75 turns.

50. A control power transformer...
Current that changes constantly in magnitude and periodically in direction.
Lower current and higher voltage.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Nearly constant.