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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
H terminals.
Because less current flowing at high voltage causes less line loss per kilowatt.
480 volts.

2. Define alternating current...
75 turns.
Potential transformer.
Current changing constantly in magnitude and periodically in direction.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

3. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Four times less than that of the secondary.
7 -630 volts.
Squirrel-cage induction motor.
Two speeds

4. Not a symptom of electrical shock?.
Stator windings.
Hyperventilation.
Derive a neutral for grounding purposes.
A step-up transformer.

5. 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?
Draw less current.
800 volts.
5:1
A step-up transformer.

6. A solenoid coil is...
H terminals.
15 feet off the ground.
An electromagnet.
At the source transformer.

7. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
Provides single-phase power to smaller loads such as lights - heaters - etc.
800 volts.
100 volts.

8. The combined capacitance of two capacitors in parallel is...
Second-degree burn.
Squirrel-cage rotor.
75 turns.
The sum of the two capacitors.

9. The property of an electrical circuit that opposes any change in voltage is called...
X.
Four times less than that of the secondary.
A grounding resistor.
Capacitance.

10. 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.
25 feet.
5:1.
Squirrel-cage induction motor.
A.C.

11. Which of the following does a squirrel cage induction motor have?
Second-degree burn.
Stator windings.
100 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.

12. Current transformers - or CT's - are used to...
Continuous.
No.6 AWG.
Reverse any two-phase leads.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

13. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Full-load - three-phase voltage.
Capacitance.
They should be made by the same manufacturer.
No.6 AWG.

14. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
A device used to store electrical energy.
15 feet off the ground.
Squirrel-cage induction motor.

15. Operating coils - motors - transformers - relays and solenoids depend upon...
A device used to store electrical energy.
Electro-magnetism for their operation.
Kilovolt ampere (KVA).
Lower current and higher voltage

16. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
12 to 15 times a minute.
The motor rotation is reversed.
Lower current and higher voltage.

17. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Circuit Breaker.
H terminals.
The motor rotation is reversed.
25 feet.

18. Alternating current may be defined as...
5:1.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Hyperventilation.
Current that changes constantly in magnitude and periodically in direction.

19. A burn causing a blister is classified as a...
X.
Second-degree burn.
100 volts.
Lower current and higher voltage

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...
100 turns.
Nearly constant.
Tied together
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

21. 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?
Disconnect the frame-grounding conductor.
3 -979 Volts.
Draw less current.
Provides single-phase power to smaller loads such as lights - heaters - etc.

22. AC voltage is raised or lowered by means of...
2000 watts
Clamp-on ammeter.
277 volts.
Transformers.

23. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
A.C.
Second-degree burn.
Squirrel-cage rotor.
The capacitors should be discharged.

24. 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?
The current will read zero.
600 volts.
Inductance.
Because less current flowing at high voltage causes less line loss per kilowatt.

25. What is a capacitor?
A device used to store electrical energy.
Electro-magnetism for their operation.
The capacitors should be discharged.
Transformer

26. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Carotid pulse - which is located in the neck next to the Adam's apple.
Because less current flowing at high voltage causes less line loss per kilowatt.
1 amp.
Full-load - three-phase voltage.

27. The primary function of a power transformer is to provide...
277 volts.
Full-load - three-phase voltage.
200 volts AC.
600 volts.

28. The property of an electric circuit that opposes any change in current is called...
Inductance.
Zero amps.
Reverse any two-phase leads.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

29. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
An electromagnet.
Lower current and higher voltage.
Short-circuited after power has been removed.

30. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Inductance.
Circuit Breaker.
A grounding resistor.
Clamp-on ammeter.

31. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Full-load - three-phase voltage.
Transformers.
480 volts.
Stator windings.

32. Three-phase AC underground cables must be provided with overcurrent protection using a...
Hyperventilation.
No.6 AWG.
X.
Circuit Breaker.

33. Where should grounding resistors be located?
Kilovolt ampere (KVA).
At the source transformer.
A grounding resistor.
Derive a neutral for grounding purposes.

34. What is the first step to be followed in aiding a victim of electrical shock?
X.
The chest should rise or inflate.
Allow for metering voltage and Current.
Check to make sure that the victim is not still in contact with the electricity.

35. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Alternating current.
The motor rotation is reversed.
12 to 15 times a minute.
Transformers.

36. Not true about AC power?
It provides good speed control.
Second-degree burn.
Check to make sure that the victim is not still in contact with the electricity.
25 feet.

37. What should the duty rating of a grounding resistor be?
The sum of the two capacitors.
Continuous.
800 volts.
Draw less current.

38. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
1 amp.
Draw less current.
2000 watts
5:1.

39. The speed of an alternating current - squirrel-cage induction motor is...
An electromagnet.
Potential transformer.
2000 watts
Nearly constant.

40. How should clothing be removed from a burn?
Inductance.
A device used to store electrical energy.
800 volts.
Cut around clothing that has adhered to the burned area.

41. What is the danger when working around capacitors?
Because less current flowing at high voltage causes less line loss per kilowatt.
The capacitors should be discharged.
An electrical shock hazard may exist.
Potential transformer.

42. 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?
At the source transformer.
2000 watts
Squirrel-cage induction motor.
150 turns.

43. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
60 cycles per second (60 Hertz).
Provides single-phase power to smaller loads such as lights - heaters - etc.
Hyperventilation.

44. To protect against over-current in a three-phase circuit over-current protection must be provided for...
The current will read zero.
Reverse any two-phase leads.
At least two phases
Full-load - three-phase voltage.

45. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
5:1
Grounded phase and ground fault devices were not operating.
Second-degree burn.
Carotid pulse - which is located in the neck next to the Adam's apple.

46. 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...
Derive a neutral for grounding purposes.
Hyperventilation.
Reverse any two-phase leads.
100 volts.

47. The transformer used only to measure voltage is a...
Potential transformer.
Larger than that found in the primary winding.
75 turns.
Second-degree burn.

48. 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.
5:1
At least two phases
Second-degree burn.
Larger than that found in the primary winding.

49. 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.
Check to make sure that the victim is not still in contact with the electricity.
Allow for metering voltage and Current.
Derive a neutral for grounding purposes.

50. What type of 3-phase AC motor is used most often around a mine?
Electro-magnetism for their operation.
75 turns.
7 -630 volts.
Squirrel-cage induction motor.