Test your basic knowledge |

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 property of an electrical circuit that opposes any change in voltage is called...
Full-load - three-phase voltage.
200 volts AC.
Capacitance.
Tied together

2. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
200 volts AC.
Clamp-on ammeter.
Transformer

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

Warning: Invalid argument supplied for foreach() in /var/www/html/basicversity.com/show_quiz.php on line 183

4. Which of the following does a squirrel cage induction motor have?
Stator windings.
75 turns.
Alternating current.
Two speeds

5. 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?
Because less current flowing at high voltage causes less line loss per kilowatt.
The capacitors should be discharged.
100 turns.
Capacitance.

6. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Nearly constant.
The chest should rise or inflate.
An electrical shock hazard may exist.
They should be made by the same manufacturer.

7. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
Reverse its rotation.
Full-load - three-phase voltage.
Inductance.

8. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Four times less than that of the secondary.
A.C.
Cut around clothing that has adhered to the burned area.

9. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
Larger than that found in the primary winding.
5:1.
100 volts.

10. What type motor is a wound-rotor induction motor?
A.C.
Potential transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
480 volts.

11. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
277 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Draw less current.

12. 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.
5:1
12 to 15 times a minute.
It provides good speed control.
5:1.

13. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Second-degree burn.
Shunted and taped
Zero amps.
7 -630 volts.

14. High voltage is used to transmit power over long distances...
Inductance.
Because less current flowing at high voltage causes less line loss per kilowatt.
100 volts.
Derive a neutral for grounding purposes.

15. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Allow for metering voltage and Current.
7 -630 volts.
Lower current and higher voltage
1 amp.

16. The property of an electric circuit that opposes any change in current is called...
Nearly constant.
Squirrel-cage rotor.
Inductance.
60 Hertz

17. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
They should be made by the same manufacturer.
No.6 AWG.
480 volts.

18. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The motor rotation is reversed.
1 amp.
A step-up transformer.
Cut around clothing that has adhered to the burned area.

19. The primary leads of a single-phase transformer should be connected to the...
At the source transformer.
H terminals.
Tied together
3 -979 Volts.

20. The combined capacitance of two capacitors in parallel is...
Zero amps.
Disconnect the frame-grounding conductor.
The sum of the two capacitors.
Capacitance.

21. Not an acceptable method for the installations of surface transformers?
60 cycles per second (60 Hertz).
The chest should rise or inflate.
They must be installed at least 7 feet above the ground.
At the source transformer.

22. The primary function of a power transformer is to provide...
75 turns.
Full-load - three-phase voltage.
Potential transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.

23. At what rate should mouth-to-mouth resuscitation be applied?
60 cycles per second (60 Hertz).
75 turns.
Check to make sure that the victim is not still in contact with the electricity.
12 to 15 times a minute.

24. AC voltage is raised or lowered by means of...
X.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Transformers.
Larger than that found in the primary winding.

25. Current in an AC circuit may be measured by...
Clamp-on ammeter.
75 turns.
3 -979 Volts.
150 turns.

26. A transformer with a 1:1 ratio is usually a (an)...
200 volts AC.
Four times less than that of the secondary.
Isolation transformer.
Disconnect the frame-grounding conductor.

27. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Check to make sure that the victim is not still in contact with the electricity.
15 feet off the ground.
Transformers.
Lower current and higher voltage.

28. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
100 turns.
Alternating current.
Two speeds
25 feet.

29. 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.
Circuit Breaker.
60 Hertz
Current changing constantly in magnitude and periodically in direction.

30. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
Zero amps.
277 volts.
7 -630 volts.

31. What is the first step to be followed in aiding a victim of electrical shock?
60 Hertz
Check to make sure that the victim is not still in contact with the electricity.
150 turns.
A.C.

32. 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?
Disconnect the frame-grounding conductor.
150 turns.
75 turns.
Provides single-phase power to smaller loads such as lights - heaters - etc.

33. 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.
Circuit Breaker.
An electrical shock hazard may exist.
The motor rotation is reversed.

34. The size of a transformer is measured in...
Draw less current.
Carotid pulse - which is located in the neck next to the Adam's apple.
Continuous.
Kilovolt ampere (KVA).

35. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Draw less current.
The current will read zero.
Because less current flowing at high voltage causes less line loss per kilowatt.
Draw less current.

36. Not a symptom of electrical shock?.
Hyperventilation.
The capacitors should be discharged.
Capacitance.
12 to 15 times a minute.

37. If any two-phase wires are reversed on a three-phase motor - the motor will...
Because less current flowing at high voltage causes less line loss per kilowatt.
Reverse its rotation.
600 volts.
Circuit Breaker.

38. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
Current changing constantly in magnitude and periodically in direction.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
7 -630 volts.

39. 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.
Lower current and higher voltage.
5:1
Allow for metering voltage and Current.
The sum of the two capacitors.

40. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
X.
Stator windings.
The capacitors should be discharged.
Circuit Breaker.

41. What is a capacitor?
5:1.
25 feet.
75 turns.
A device used to store electrical energy.

42. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
277 volts.
No.6 AWG.
Carotid pulse - which is located in the neck next to the Adam's apple.
Transformer

43. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
The chest should rise or inflate.
An electromagnet.
Circuit Breaker.

44. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
H terminals.
Allow for metering voltage and Current.
5:1.

45. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Cut around clothing that has adhered to the burned area.
600 volts.
A grounding resistor.
Second-degree burn.

46. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
An electromagnet.
Four times less than that of the secondary.
60 cycles per second (60 Hertz).

47. What should the duty rating of a grounding resistor be?
600 volts.
It provides good speed control.
Nearly constant.
Continuous.

48. 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...
Alternating current.
Draw less current.
Cut around clothing that has adhered to the burned area.
Hyperventilation.

49. The standard frequency of alternating current used at a mine is...
Allow for metering voltage and Current.
At the source transformer.
60 Hertz
X.

50. All transformers step voltage up or down by...
Four times less than that of the secondary.
Inductance.
They should be made by the same manufacturer.
Second-degree burn.