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. If any two-phase wires are reversed on a three-phase motor - the motor will...
Cut around clothing that has adhered to the burned area.
Reverse its rotation.
Zero amps.
The sum of the two capacitors.

2. What is a capacitor?
Transformer
A device used to store electrical energy.
25 feet.
Provides single-phase power to smaller loads such as lights - heaters - etc.

3. Which of the following does a squirrel cage induction motor have?
60 cycles per second (60 Hertz).
Alternating current.
Stator windings.
Kilovolt ampere (KVA).

4. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
They should be made by the same manufacturer.
25 feet.
100 turns.
H terminals.

5. What type motor is a wound-rotor induction motor?
200 volts AC.
100 turns.
A grounding resistor.
A.C.

6. When not connected to a load - the secondary leads of a current transformer should be...
At the source transformer.
Carotid pulse - which is located in the neck next to the Adam's apple.
Shunted and taped
Allow for metering voltage and Current.

7. The property of an electric circuit that opposes any change in current is called...
75 turns.
Inductance.
Capacitance.
600 volts.

8. The standard frequency of power supplied by the power company is...
800 volts.
Reverse its rotation.
75 turns.
60 cycles per second (60 Hertz).

9. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
Transformers.
The capacitors should be discharged.
Disconnect the frame-grounding conductor.

10. A transformer with a 1:1 ratio is usually a (an)...
The current will read zero.
Alternating current.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Isolation transformer.

11. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Squirrel-cage rotor.
Inductance.
12 to 15 times a minute.

12. Define alternating current...
Alternating current.
Two speeds
Isolation transformer.
Current changing constantly in magnitude and periodically in direction.

13. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
The chest should rise or inflate.
200 volts AC.
480 volts.
A grounding resistor.

14. Operating coils - motors - transformers - relays and solenoids depend upon...
The current will read zero.
7 -630 volts.
Grounded phase and ground fault devices were not operating.
Electro-magnetism for their operation.

15. How do you change the direction of a 3-phase AC motor?
At the source transformer.
A step-up transformer.
Tied together
Reverse any two-phase leads.

16. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Inductance.
Draw less current.
At least two phases
An electromagnet.

17. How should clothing be removed from a burn?
Two speeds
A step-up transformer.
Cut around clothing that has adhered to the burned area.
150 turns.

18. Not true about AC power?
60 Hertz
It provides good speed control.
Lower current and higher voltage
75 turns.

19. The combined capacitance of two capacitors in parallel is...
Potential transformer.
Reverse any two-phase leads.
Transformer
The sum of the two capacitors.

20. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Zero amps.
480 volts.
Squirrel-cage induction motor.

21. Current that changes periodically in direction is...
60 cycles per second (60 Hertz).
Alternating current.
Provides single-phase power to smaller loads such as lights - heaters - etc.
The motor rotation is reversed.

22. The speed of an alternating current - squirrel-cage induction motor is...
5:1.
Nearly constant.
The motor rotation is reversed.
Reverse any two-phase leads.

23. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
2000 watts
Draw less current.
75 turns.
150 turns.

24. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Circuit Breaker.
Inductance.
Kilovolt ampere (KVA).

25. 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...
277 volts.
At the source transformer.
Continuous.
Draw less current.

26. 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?
Reverse its rotation.
100 turns.
Transformers.
Draw less current.

27. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Inductance.
A.C.
7 -630 volts.
No.6 AWG.

28. At what rate should mouth-to-mouth resuscitation be applied?
An electrical shock hazard may exist.
12 to 15 times a minute.
Grounded phase and ground fault devices were not operating.
60 Hertz

29. All transformers step voltage up or down by...
25 feet.
Potential transformer.
Inductance.
Check to make sure that the victim is not still in contact with the electricity.

30. What is the danger when working around capacitors?
Alternating current.
1 amp.
An electrical shock hazard may exist.
Full-load - three-phase voltage.

31. What steps up or steps down AC voltage?
Transformer
The chest should rise or inflate.
Inductance.
X.

32. The purpose of a zig-zag transformer is to...
Electro-magnetism for their operation.
Inductance.
The sum of the two capacitors.
Derive a neutral for grounding purposes.

33. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
5:1.
An electrical shock hazard may exist.
25 feet.

34. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Derive a neutral for grounding purposes.
5:1.
Draw less current.

35. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Stator windings.
Current changing constantly in magnitude and periodically in direction.
A step-up transformer.
Larger than that found in the primary winding.

36. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Zero amps.
Provides single-phase power to smaller loads such as lights - heaters - etc.
100 volts.
A grounding resistor.

37. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
100 turns.
Lower current and higher voltage
X.
Short-circuited after power has been removed.

38. What is the first step to be followed in aiding a victim of electrical shock?
Continuous.
Check to make sure that the victim is not still in contact with the electricity.
60 Hertz
Alternating current.

39. 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?
Circuit Breaker.
277 volts.
Lower current and higher voltage
600 volts.

40. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
480 volts.
The chest should rise or inflate.
Hyperventilation.

41. 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...
Draw less current.
277 volts.
It provides good speed control.
60 Hertz

42. 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.
3 -979 Volts.
No.6 AWG.
5:1
The motor rotation is reversed.

43. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Tied together
Continuous.
No.6 AWG.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

44. 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.
150 turns.
Current that changes constantly in magnitude and periodically in direction.
Draw less current.

45. What should the duty rating of a grounding resistor be?
Stator windings.
It provides good speed control.
2000 watts
Continuous.

46. Current transformers - or CT's - are used to...
Isolation transformer.
2000 watts
No.6 AWG.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

47. 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.
Zero amps.
A step-up transformer.
Inductance.

48. A control power transformer...
Isolation transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
15 feet off the ground.
Provides single-phase power to smaller loads such as lights - heaters - etc.

49. What type of 3-phase AC motor is used most often around a mine?
At least two phases
200 volts AC.
Squirrel-cage induction motor.
800 volts.

50. Current in an AC circuit may be measured by...
A step-up transformer.
Clamp-on ammeter.
A grounding resistor.
Reverse its rotation.