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. What position of a selector switch using a voltmeter would you select to check a 120-volt AC circuit to obtain the most accurate reading?
A device used to store electrical energy.
200 volts AC.
Clamp-on ammeter.
Shunted and taped

2. A transformer with a 1:1 ratio is usually a (an)...
The sum of the two capacitors.
Circuit Breaker.
Isolation transformer.
277 volts.

3. The transformer used only to measure voltage is a...
The sum of the two capacitors.
Potential transformer.
Transformer
Derive a neutral for grounding purposes.

4. A control power transformer...
Second-degree burn.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Reverse its rotation.
Transformers.

5. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
A grounding resistor.
No.6 AWG.
Nearly constant.
The sum of the two capacitors.

6. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Draw less current.
1 amp.
At the source transformer.
Second-degree burn.

7. Compared to the secondary of a loaded - step-down transformer - the primary has...
At least two phases
Lower current and higher voltage
The current will read zero.
Short-circuited after power has been removed.

8. Not a symptom of electrical shock?.
5:1
Transformers.
Hyperventilation.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

9. 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.
Inductance.
Squirrel-cage induction motor.

10. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
Hyperventilation.
Squirrel-cage induction motor.
An electrical shock hazard may exist.

11. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
200 volts AC.
25 feet.
Lower current and higher voltage.
Shunted and taped

12. Which of the following does a squirrel cage induction motor have?
Stator windings.
Potential transformer.
The capacitors should be discharged.
Clamp-on ammeter.

13. Not an acceptable method for the installations of surface transformers?
A.C.
They must be installed at least 7 feet above the ground.
Reverse its rotation.
7 -630 volts.

14. High voltage is used to transmit power over long distances...
7 -630 volts.
100 turns.
5:1.
Because less current flowing at high voltage causes less line loss per kilowatt.

15. What is a capacitor?
Two speeds
A step-up transformer.
Short-circuited after power has been removed.
A device used to store electrical energy.

16. 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?
The sum of the two capacitors.
Allow for metering voltage and Current.
800 volts.
100 turns.

17. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Electro-magnetism for their operation.
Grounded phase and ground fault devices were not operating.
Lower current and higher voltage.

18. 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...
Hyperventilation.
Draw less current.
100 volts.
Short-circuited after power has been removed.

19. 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
At least two phases
Squirrel-cage induction motor.
Alternating current.

20. 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...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Draw less current.
The chest should rise or inflate.
Full-load - three-phase voltage.

21. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Provides single-phase power to smaller loads such as lights - heaters - etc.
Two speeds
A grounding resistor.
7 -630 volts.

22. What is the first step to be followed in aiding a victim of electrical shock?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
An electromagnet.
Grounded phase and ground fault devices were not operating.
Check to make sure that the victim is not still in contact with the electricity.

23. What type motor is a wound-rotor induction motor?
Continuous.
Draw less current.
Potential transformer.
A.C.

24. 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?
At least two phases
Second-degree burn.
3 -979 Volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

25. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
The current will read zero.
Shunted and taped
Electro-magnetism for their operation.

26. The combined capacitance of two capacitors in parallel is...
Grounded phase and ground fault devices were not operating.
The sum of the two capacitors.
600 volts.
1 amp.

27. How do you change the direction of a 3-phase AC motor?
Short-circuited after power has been removed.
3 -979 Volts.
Allow for metering voltage and Current.
Reverse any two-phase leads.

28. The size of a transformer is measured in...
Kilovolt ampere (KVA).
A device used to store electrical energy.
The current will read zero.
Squirrel-cage rotor.

29. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Squirrel-cage rotor.
480 volts.
They must be installed at least 7 feet above the ground.
A step-up transformer.

30. The primary leads of a single-phase transformer should be connected to the...
An electromagnet.
The capacitors should be discharged.
H terminals.
100 turns.

31. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Inductance.
Derive a neutral for grounding purposes.
At least two phases
Clamp-on ammeter.

32. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Transformers.
The motor rotation is reversed.
Shunted and taped
Potential transformer.

33. A burn causing a blister is classified as a...
Kilovolt ampere (KVA).
Circuit Breaker.
150 turns.
Second-degree burn.

34. AC voltage is raised or lowered by means of...
Transformers.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
12 to 15 times a minute.
Short-circuited after power has been removed.

35. Not true about AC power?
It provides good speed control.
Cut around clothing that has adhered to the burned area.
Nearly constant.
60 cycles per second (60 Hertz).

36. A solenoid coil is...
1 amp.
Two speeds
An electromagnet.
2000 watts

37. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
25 feet.
Squirrel-cage induction motor.
Isolation transformer.
The current will read zero.

38. Where should grounding resistors be located?
Check to make sure that the victim is not still in contact with the electricity.
At the source transformer.
25 feet.
Transformers.

39. What type of 3-phase AC motor is used most often around a mine?
Continuous.
Provides single-phase power to smaller loads such as lights - heaters - etc.
A.C.
Squirrel-cage induction motor.

40. What steps up or steps down AC voltage?
H terminals.
3 -979 Volts.
Transformer
5:1.

41. The main function of CT's and PT's on a main substation is to...
Cut around clothing that has adhered to the burned area.
Derive a neutral for grounding purposes.
A grounding resistor.
Allow for metering voltage and Current.

42. Current transformers - or CT's - are used to...
5:1
Kilovolt ampere (KVA).
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Full-load - three-phase voltage.

43. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Allow for metering voltage and Current.
A step-up transformer.
Clamp-on ammeter.
Draw less current.

44. 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.
The current will read zero.
Because less current flowing at high voltage causes less line loss per kilowatt.
Shunted and taped

45. If any two-phase wires are reversed on a three-phase motor - the motor will...
Transformers.
Reverse its rotation.
100 turns.
Lower current and higher voltage

46. Current that changes periodically in direction is...
60 Hertz
Reverse any two-phase leads.
Shunted and taped
Alternating current.

47. 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?
200 volts AC.
75 turns.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Lower current and higher voltage

48. Alternating current may be defined as...
Tied together
5:1.
Current that changes constantly in magnitude and periodically in direction.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

49. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Lower current and higher voltage.
Inductance.
The chest should rise or inflate.
Derive a neutral for grounding purposes.

50. 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.
1 amp.
25 feet.