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 secondary windings on a 10:1 step-down transformer will have a wire size...
The current will read zero.
Larger than that found in the primary winding.
75 turns.
5:1

2. 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...
100 volts.
Reverse its rotation.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Squirrel-cage induction motor.

3. The size of a transformer is measured in...
H terminals.
Second-degree burn.
Short-circuited after power has been removed.
Kilovolt ampere (KVA).

4. 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.
Allow for metering voltage and Current.
60 cycles per second (60 Hertz).
Because less current flowing at high voltage causes less line loss per kilowatt.
5:1

5. What should the duty rating of a grounding resistor be?
Kilovolt ampere (KVA).
The motor rotation is reversed.
Continuous.
75 turns.

6. What is the first step to be followed in aiding a victim of electrical shock?
Second-degree burn.
Hyperventilation.
Cut around clothing that has adhered to the burned area.
Check to make sure that the victim is not still in contact with the electricity.

7. 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.
Squirrel-cage induction motor.
At least two phases
277 volts.

8. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
7 -630 volts.
Clamp-on ammeter.
The motor rotation is reversed.

9. What is the danger when working around capacitors?
Tied together
100 turns.
Stator windings.
An electrical shock hazard may exist.

10. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
A.C.
15 feet off the ground.
Disconnect the frame-grounding conductor.
60 cycles per second (60 Hertz).

11. The transformer used only to measure voltage is a...
Potential transformer.
600 volts.
It provides good speed control.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

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?
Disconnect the frame-grounding conductor.
An electromagnet.
Kilovolt ampere (KVA).
75 turns.

13. 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.
A.C.
Zero amps.
Current that changes constantly in magnitude and periodically in direction.

14. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
75 turns.
Inductance.
Zero amps.

15. Not a symptom of electrical shock?.
277 volts.
Transformers.
Hyperventilation.
Kilovolt ampere (KVA).

16. 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.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Tied together

17. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Inductance.
They must be installed at least 7 feet above the ground.
Two speeds
25 feet.

18. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
The motor rotation is reversed.
Two speeds
1 amp.
X.

19. 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?
75 turns.
At the source transformer.
150 turns.
Alternating current.

20. 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?
Inductance.
100 turns.
At the source transformer.
The current will read zero.

21. The primary function of a power transformer is to provide...
Larger than that found in the primary winding.
Full-load - three-phase voltage.
1 amp.
Current that changes constantly in magnitude and periodically in direction.

22. 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.
Nearly constant.
5:1.
It provides good speed control.
At the source transformer.

23. What steps up or steps down AC voltage?
600 volts.
15 feet off the ground.
Disconnect the frame-grounding conductor.
Transformer

24. The property of an electrical circuit that opposes any change in voltage is called...
277 volts.
Capacitance.
2000 watts
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

25. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Circuit Breaker.
100 turns.
Four times less than that of the secondary.
Disconnect the frame-grounding conductor.

26. What type motor is a wound-rotor induction motor?
A.C.
Derive a neutral for grounding purposes.
75 turns.
100 turns.

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

28. What is a capacitor?
A device used to store electrical energy.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Inductance.
200 volts AC.

29. Not an acceptable method for the installations of surface transformers?
Draw less current.
They must be installed at least 7 feet above the ground.
480 volts.
Kilovolt ampere (KVA).

30. The property of an electric circuit that opposes any change in current is called...
Nearly constant.
Larger than that found in the primary winding.
Check to make sure that the victim is not still in contact with the electricity.
Inductance.

31. Define alternating current...
1 amp.
Stator windings.
Continuous.
Current changing constantly in magnitude and periodically in direction.

32. When not connected to a load - the secondary leads of a current transformer should be...
An electromagnet.
15 feet off the ground.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Shunted and taped

33. How do you change the direction of a 3-phase AC motor?
Short-circuited after power has been removed.
100 turns.
Reverse any two-phase leads.
It provides good speed control.

34. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
A device used to store electrical energy.
2000 watts

35. The purpose of a zig-zag transformer is to...
Lower current and higher voltage.
Grounded phase and ground fault devices were not operating.
Derive a neutral for grounding purposes.
75 turns.

36. A burn causing a blister is classified as a...
2000 watts
An electrical shock hazard may exist.
Second-degree burn.
7 -630 volts.

37. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Short-circuited after power has been removed.
An electrical shock hazard may exist.
Carotid pulse - which is located in the neck next to the Adam's apple.
A step-up transformer.

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.
60 Hertz
Inductance.
The capacitors should be discharged.

39. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Electro-magnetism for their operation.
Squirrel-cage induction motor.
Four times less than that of the secondary.
75 turns.

40. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
An electromagnet.
2000 watts
Zero amps.
Nearly constant.

41. A solenoid coil is...
The sum of the two capacitors.
An electromagnet.
An electrical shock hazard may exist.
100 turns.

42. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Short-circuited after power has been removed.
Shunted and taped
At the source transformer.
Draw less current.

43. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A grounding resistor.
15 feet off the ground.
At least two phases
800 volts.

44. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
100 turns.
The current will read zero.
Reverse any two-phase leads.
60 Hertz

45. The main function of CT's and PT's on a main substation is to...
Draw less current.
Reverse its rotation.
Allow for metering voltage and Current.
It provides good speed control.

46. Operating coils - motors - transformers - relays and solenoids depend upon...
75 turns.
150 turns.
Electro-magnetism for their operation.
They should be made by the same manufacturer.

47. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
The sum of the two capacitors.
Kilovolt ampere (KVA).
Second-degree burn.
They should be made by the same manufacturer.

48. AC voltage is raised or lowered by means of...
Transformers.
Alternating current.
The motor rotation is reversed.
Kilovolt ampere (KVA).

49. Which of the following does a squirrel cage induction motor have?
Stator windings.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Squirrel-cage induction motor.
Transformer

50. The combined capacitance of two capacitors in parallel is...
The chest should rise or inflate.
Nearly constant.
The sum of the two capacitors.
Four times less than that of the secondary.