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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. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Reverse its rotation.
600 volts.
5:1.

2. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
H terminals.
2000 watts
15 feet off the ground.
Capacitance.

3. How should clothing be removed from a burn?
An electromagnet.
Cut around clothing that has adhered to the burned area.
Electro-magnetism for their operation.
Allow for metering voltage and Current.

4. The primary leads of a single-phase transformer should be connected to the...
H terminals.
2000 watts
60 cycles per second (60 Hertz).
At the source transformer.

5. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Circuit Breaker.
2000 watts
Second-degree burn.
H terminals.

6. All transformers step voltage up or down by...
Squirrel-cage induction motor.
Inductance.
The motor rotation is reversed.
5:1

7. When not connected to a load - the secondary leads of a current transformer should be...
Zero amps.
Four times less than that of the secondary.
Shunted and taped
Grounded phase and ground fault devices were not operating.

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?
Shunted and taped
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Reverse its rotation.
600 volts.

9. Where should grounding resistors be located?
At the source transformer.
3 -979 Volts.
A grounding resistor.
An electromagnet.

10. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
480 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
800 volts.
The chest should rise or inflate.

11. The property of an electric circuit that opposes any change in current is called...
Four times less than that of the secondary.
2000 watts
Zero amps.
Inductance.

12. 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?
800 volts.
No.6 AWG.
Kilovolt ampere (KVA).
Derive a neutral for grounding purposes.

13. What steps up or steps down AC voltage?
Current that changes constantly in magnitude and periodically in direction.
Second-degree burn.
75 turns.
Transformer

14. What should the duty rating of a grounding resistor be?
Continuous.
No.6 AWG.
480 volts.
200 volts AC.

15. 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?
100 turns.
150 turns.
5:1
600 volts.

16. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
100 volts.
Lower current and higher voltage
The current will read zero.

17. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The current will read zero.
Capacitance.
Isolation transformer.
Shunted and taped

18. 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?
Allow for metering voltage and Current.
Circuit Breaker.
100 turns.
It provides good speed control.

19. Which of the following does a squirrel cage induction motor have?
Two speeds
5:1.
Stator windings.
A device used to store electrical energy.

20. A wound-rotor induction motor has all the following EXCEPT...
Potential transformer.
Squirrel-cage rotor.
It provides good speed control.
Circuit Breaker.

21. The combined capacitance of two capacitors in parallel is...
Draw less current.
The motor rotation is reversed.
The sum of the two capacitors.
Alternating current.

22. Three-phase AC underground cables must be provided with overcurrent protection using a...
5:1
Grounded phase and ground fault devices were not operating.
Circuit Breaker.
600 volts.

23. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Allow for metering voltage and Current.
277 volts.
Clamp-on ammeter.
Draw less current.

24. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Reverse any two-phase leads.
Short-circuited after power has been removed.
A step-up transformer.
They should be made by the same manufacturer.

25. 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?
Four times less than that of the secondary.
Check to make sure that the victim is not still in contact with the electricity.
Cut around clothing that has adhered to the burned area.
3 -979 Volts.

26. The primary function of a power transformer is to provide...
Four times less than that of the secondary.
Full-load - three-phase voltage.
75 turns.
Alternating current.

27. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
The capacitors should be discharged.
Four times less than that of the secondary.
Squirrel-cage rotor.
The motor rotation is reversed.

28. 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
100 turns.
Alternating current.
5:1.

29. What is a capacitor?
Allow for metering voltage and Current.
A device used to store electrical energy.
Current changing constantly in magnitude and periodically in direction.
75 turns.

30. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
150 turns.
X.
Transformer

31. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
A.C.
12 to 15 times a minute.
Grounded phase and ground fault devices were not operating.
Reverse its rotation.

32. What type motor is a wound-rotor induction motor?
Draw less current.
Draw less current.
A device used to store electrical energy.
A.C.

33. Not a symptom of electrical shock?.
Current changing constantly in magnitude and periodically in direction.
A step-up transformer.
Hyperventilation.
H terminals.

34. Operating coils - motors - transformers - relays and solenoids depend upon...
7 -630 volts.
Circuit Breaker.
Electro-magnetism for their operation.
The chest should rise or inflate.

35. The purpose of a zig-zag transformer is to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Full-load - three-phase voltage.
Derive a neutral for grounding purposes.
A.C.

36. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
800 volts.
Stator windings.
7 -630 volts.
75 turns.

37. At what rate should mouth-to-mouth resuscitation be applied?
1 amp.
12 to 15 times a minute.
H terminals.
800 volts.

38. 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.
Larger than that found in the primary winding.
Reverse any two-phase leads.
They must be installed at least 7 feet above the ground.
5:1

39. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Capacitance.
1 amp.
60 Hertz

40. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Squirrel-cage rotor.
1 amp.
A step-up transformer.
The chest should rise or inflate.

41. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
They must be installed at least 7 feet above the ground.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Nearly constant.
X.

42. The secondary windings on a 10:1 step-down transformer will have a wire size...
480 volts.
Isolation transformer.
The current will read zero.
Larger than that found in the primary winding.

43. 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.
Capacitance.
Hyperventilation.
Draw less current.
5:1.

44. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Inductance.
800 volts.
Grounded phase and ground fault devices were not operating.

45. If any two-phase wires are reversed on a three-phase motor - the motor will...
H terminals.
An electrical shock hazard may exist.
Draw less current.
Reverse its rotation.

46. The size of a transformer is measured in...
800 volts.
Kilovolt ampere (KVA).
480 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

47. Current in an AC circuit may be measured by...
Clamp-on ammeter.
5:1.
Current that changes constantly in magnitude and periodically in direction.
Larger than that found in the primary winding.

48. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Potential transformer.
No.6 AWG.
Inductance.
25 feet.

49. High voltage is used to transmit power over long distances...
75 turns.
Because less current flowing at high voltage causes less line loss per kilowatt.
1 amp.
The capacitors should be discharged.

50. A solenoid coil is...
They must be installed at least 7 feet above the ground.
480 volts.
Four times less than that of the secondary.
An electromagnet.