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 the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Inductance.
Disconnect the frame-grounding conductor.
Zero amps.
No.6 AWG.

2. Three-phase AC underground cables must be provided with overcurrent protection using a...
Carotid pulse - which is located in the neck next to the Adam's apple.
Circuit Breaker.
100 volts.
Tied together

3. Not true about AC power?
It provides good speed control.
Kilovolt ampere (KVA).
Circuit Breaker.
15 feet off the ground.

4. The secondary windings on a 10:1 step-down transformer will have a wire size...
At least two phases
The motor rotation is reversed.
Four times less than that of the secondary.
Larger than that found in the primary winding.

5. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Grounded phase and ground fault devices were not operating.
Potential transformer.
A grounding resistor.
No.6 AWG.

6. A wound-rotor induction motor has all the following EXCEPT...
277 volts.
200 volts AC.
Squirrel-cage rotor.
A.C.

7. The primary function of a power transformer is to provide...
Lower current and higher voltage
Full-load - three-phase voltage.
Draw less current.
Disconnect the frame-grounding conductor.

8. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
3 -979 Volts.
Clamp-on ammeter.

9. The size of a transformer is measured in...
100 turns.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Second-degree burn.
Kilovolt ampere (KVA).

10. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
1 amp.
200 volts AC.
2000 watts

11. What is the danger when working around capacitors?
An electrical shock hazard may exist.
A step-up transformer.
Four times less than that of the secondary.
Clamp-on ammeter.

12. The standard frequency of alternating current used at a mine is...
Electro-magnetism for their operation.
150 turns.
60 Hertz
A step-up transformer.

13. A burn causing a blister is classified as a...
Second-degree burn.
15 feet off the ground.
2000 watts
X.

14. What is a capacitor?
Cut around clothing that has adhered to the burned area.
A device used to store electrical energy.
7 -630 volts.
Lower current and higher voltage

15. What type motor is a wound-rotor induction motor?
An electromagnet.
Electro-magnetism for their operation.
A.C.
A grounding resistor.

16. What is the first step to be followed in aiding a victim of electrical shock?
Current that changes constantly in magnitude and periodically in direction.
A.C.
Check to make sure that the victim is not still in contact with the electricity.
The current will read zero.

17. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
Isolation transformer.
Full-load - three-phase voltage.
25 feet.

18. 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?
Tied together
Cut around clothing that has adhered to the burned area.
600 volts.
Transformer

19. Compared to the secondary of a loaded - step-down transformer - the primary has...
Squirrel-cage induction motor.
Lower current and higher voltage.
25 feet.
7 -630 volts.

20. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Isolation transformer.
2000 watts
Electro-magnetism for their operation.
Four times less than that of the secondary.

21. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
100 turns.
At the source transformer.
They should be made by the same manufacturer.
Stator windings.

22. How do you change the direction of a 3-phase AC motor?
7 -630 volts.
Kilovolt ampere (KVA).
75 turns.
Reverse any two-phase leads.

23. 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?
200 volts AC.
Because less current flowing at high voltage causes less line loss per kilowatt.
Current that changes constantly in magnitude and periodically in direction.
Transformers.

24. 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...
Circuit Breaker.
The capacitors should be discharged.
75 turns.
Draw less current.

25. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
An electrical shock hazard may exist.
800 volts.
Alternating current.

26. 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?
25 feet.
75 turns.
At the source transformer.
H terminals.

27. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
It provides good speed control.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Inductance.
No.6 AWG.

28. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Circuit Breaker.
Transformers.
Electro-magnetism for their operation.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

29. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
480 volts.
No.6 AWG.
An electrical shock hazard may exist.

30. Current that changes periodically in direction is...
Second-degree burn.
25 feet.
5:1.
Alternating current.

31. How should clothing be removed from a burn?
Alternating current.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Cut around clothing that has adhered to the burned area.
Short-circuited after power has been removed.

32. 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...
Transformers.
800 volts.
H terminals.
Draw less current.

33. To protect against over-current in a three-phase circuit over-current protection must be provided for...
The chest should rise or inflate.
At least two phases
Carotid pulse - which is located in the neck next to the Adam's apple.
15 feet off the ground.

34. The purpose of a zig-zag transformer is to...
Clamp-on ammeter.
The motor rotation is reversed.
Derive a neutral for grounding purposes.
12 to 15 times a minute.

35. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
7 -630 volts.
Current changing constantly in magnitude and periodically in direction.
600 volts.

36. Current transformers - or CT's - are used to...
Two speeds
Derive a neutral for grounding purposes.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Larger than that found in the primary winding.

37. What steps up or steps down AC voltage?
An electrical shock hazard may exist.
Transformer
Zero amps.
X.

38. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
The sum of the two capacitors.
At the source transformer.
277 volts.
Continuous.

39. 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.
600 volts.
Reverse its rotation.
60 cycles per second (60 Hertz).

40. Not a symptom of electrical shock?.
Draw less current.
Hyperventilation.
Inductance.
5:1.

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

42. 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?
100 turns.
Because less current flowing at high voltage causes less line loss per kilowatt.
Draw less current.
7 -630 volts.

43. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Because less current flowing at high voltage causes less line loss per kilowatt.
Reverse any two-phase leads.
Current that changes constantly in magnitude and periodically in direction.
Two speeds

44. The property of an electric circuit that opposes any change in current is called...
60 Hertz
Allow for metering voltage and Current.
Inductance.
Alternating current.

45. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Draw less current.
Zero amps.
Four times less than that of the secondary.
At least two phases

46. Where should grounding resistors be located?
Inductance.
Transformer
Transformers.
At the source transformer.

47. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Potential transformer.
25 feet.
Short-circuited after power has been removed.
Grounded phase and ground fault devices were not operating.

48. The transformer used only to measure voltage is a...
They must be installed at least 7 feet above the ground.
Short-circuited after power has been removed.
15 feet off the ground.
Potential transformer.

49. Which of the following does a squirrel cage induction motor have?
Stator windings.
7 -630 volts.
5:1
Squirrel-cage induction motor.

50. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
A step-up transformer.
Check to make sure that the victim is not still in contact with the electricity.
Lower current and higher voltage.
The chest should rise or inflate.