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. 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?
X.
600 volts.
150 turns.
Alternating current.

2. Current in an AC circuit may be measured by...
Grounded phase and ground fault devices were not operating.
Clamp-on ammeter.
Transformer
Potential transformer.

3. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Grounded phase and ground fault devices were not operating.
Circuit Breaker.
277 volts.
Transformer

4. The primary leads of a single-phase transformer should be connected to the...
H terminals.
277 volts.
A grounding resistor.
Draw less current.

5. Compared to the secondary of a loaded - step-down transformer - the primary has...
Capacitance.
Lower current and higher voltage
1 amp.
Lower current and higher voltage.

6. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
5:1.
Carotid pulse - which is located in the neck next to the Adam's apple.
Shunted and taped

7. The main function of CT's and PT's on a main substation is to...
A device used to store electrical energy.
75 turns.
Cut around clothing that has adhered to the burned area.
Allow for metering voltage and Current.

8. 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...
Full-load - three-phase voltage.
Shunted and taped
Disconnect the frame-grounding conductor.
Draw less current.

9. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
The capacitors should be discharged.
15 feet off the ground.
Squirrel-cage induction motor.

10. The speed of an alternating current - squirrel-cage induction motor is...
25 feet.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
A device used to store electrical energy.
Nearly constant.

11. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Inductance.
150 turns.
Reverse any two-phase leads.
A grounding resistor.

12. Compared to the secondary of a loaded - step-down transformer - the primary has...
Grounded phase and ground fault devices were not operating.
Second-degree burn.
Stator windings.
Lower current and higher voltage.

13. A wound-rotor induction motor has all the following EXCEPT...
15 feet off the ground.
Squirrel-cage rotor.
They should be made by the same manufacturer.
Derive a neutral for grounding purposes.

14. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
600 volts.
Nearly constant.
480 volts.
Draw less current.

15. The standard frequency of alternating current used at a mine is...
60 Hertz
Allow for metering voltage and Current.
Nearly constant.
X.

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?
Continuous.
Second-degree burn.
Circuit Breaker.
3 -979 Volts.

17. Not a symptom of electrical shock?.
Draw less current.
Kilovolt ampere (KVA).
Continuous.
Hyperventilation.

18. High voltage is used to transmit power over long distances...
75 turns.
Clamp-on ammeter.
Because less current flowing at high voltage causes less line loss per kilowatt.
Short-circuited after power has been removed.

19. Operating coils - motors - transformers - relays and solenoids depend upon...
Tied together
Electro-magnetism for their operation.
Two speeds
The sum of the two capacitors.

20. All transformers step voltage up or down by...
Inductance.
Stator windings.
Current that changes constantly in magnitude and periodically in direction.
Isolation transformer.

21. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Electro-magnetism for their operation.
75 turns.
1 amp.
Stator windings.

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

23. A control power transformer...
Shunted and taped
25 feet.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Transformers.

24. 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.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
A.C.

25. What type of 3-phase AC motor is used most often around a mine?
A device used to store electrical energy.
Squirrel-cage induction motor.
60 cycles per second (60 Hertz).
Inductance.

26. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Four times less than that of the secondary.
Squirrel-cage induction motor.
15 feet off the ground.
Reverse its rotation.

27. 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...
Draw less current.
Larger than that found in the primary winding.
200 volts AC.
An electromagnet.

28. Which of the following does a squirrel cage induction motor have?
Nearly constant.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Stator windings.
Capacitance.

29. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
At the source transformer.
The motor rotation is reversed.
100 volts.

30. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
100 turns.
Check to make sure that the victim is not still in contact with the electricity.
Continuous.
The capacitors should be discharged.

31. Alternating current may be defined as...
A step-up transformer.
An electromagnet.
7 -630 volts.
Current that changes constantly in magnitude and periodically in direction.

32. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Electro-magnetism for their operation.
Two speeds
At the source transformer.
25 feet.

33. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
1 amp.
60 cycles per second (60 Hertz).
An electromagnet.

34. The purpose of a zig-zag transformer is to...
No.6 AWG.
15 feet off the ground.
Electro-magnetism for their operation.
Derive a neutral for grounding purposes.

35. 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?
75 turns.
Inductance.
Cut around clothing that has adhered to the burned area.
Inductance.

36. The secondary windings on a 10:1 step-down transformer will have a wire size...
Shunted and taped
Larger than that found in the primary winding.
The capacitors should be discharged.
12 to 15 times a minute.

37. Not true about AC power?
They should be made by the same manufacturer.
The capacitors should be discharged.
It provides good speed control.
Grounded phase and ground fault devices were not operating.

38. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Current changing constantly in magnitude and periodically in direction.
They should be made by the same manufacturer.
Check to make sure that the victim is not still in contact with the electricity.
Provides single-phase power to smaller loads such as lights - heaters - etc.

39. If any two-phase wires are reversed on a three-phase motor - the motor will...
Two speeds
It provides good speed control.
Draw less current.
Reverse its rotation.

40. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Squirrel-cage induction motor.
15 feet off the ground.
No.6 AWG.

41. What is the danger when working around capacitors?
Because less current flowing at high voltage causes less line loss per kilowatt.
100 turns.
Check to make sure that the victim is not still in contact with the electricity.
An electrical shock hazard may exist.

42. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
They should be made by the same manufacturer.
Continuous.
Circuit Breaker.

43. 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?
75 turns.
At the source transformer.
Larger than that found in the primary winding.
Shunted and taped

44. 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...
Continuous.
Allow for metering voltage and Current.
Electro-magnetism for their operation.
Tied together

45. 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.
The motor rotation is reversed.
A.C.
Reverse its rotation.

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...
Nearly constant.
7 -630 volts.
100 volts.
A device used to store electrical energy.

47. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Tied together
Isolation transformer.
Potential transformer.

48. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
12 to 15 times a minute.
Squirrel-cage induction motor.
Draw less current.
Grounded phase and ground fault devices were not operating.

49. Current that changes periodically in direction is...
X.
1 amp.
Alternating current.
Current changing constantly in magnitude and periodically in direction.

50. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
The sum of the two capacitors.
Grounded phase and ground fault devices were not operating.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
X.