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?
Kilovolt ampere (KVA).
Zero amps.
The capacitors should be discharged.
Squirrel-cage induction motor.

2. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
600 volts.
Reverse its rotation.
Four times less than that of the secondary.
A step-up transformer.

3. Current that changes periodically in direction is...
3 -979 Volts.
Alternating current.
No.6 AWG.
Shunted and taped

4. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Electro-magnetism for their operation.
Short-circuited after power has been removed.
Zero amps.
15 feet off the ground.

5. How do you change the direction of a 3-phase AC motor?
Cut around clothing that has adhered to the burned area.
Inductance.
Reverse any two-phase leads.
Current that changes constantly in magnitude and periodically in direction.

6. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A.C.
3 -979 Volts.
The capacitors should be discharged.
A grounding resistor.

7. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
H terminals.
75 turns.
Alternating current.

8. The standard frequency of power supplied by the power company is...
480 volts.
The chest should rise or inflate.
60 cycles per second (60 Hertz).
Disconnect the frame-grounding conductor.

9. High voltage is used to transmit power over long distances...
600 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Two speeds
Because less current flowing at high voltage causes less line loss per kilowatt.

10. 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...
Tied together
X.
Larger than that found in the primary winding.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

11. What type of 3-phase AC motor is used most often around a mine?
Inductance.
X.
The capacitors should be discharged.
Squirrel-cage induction motor.

12. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Inductance.
X.
H terminals.
Because less current flowing at high voltage causes less line loss per kilowatt.

13. What is a capacitor?
Squirrel-cage rotor.
Lower current and higher voltage
Inductance.
A device used to store electrical energy.

14. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Capacitance.
Short-circuited after power has been removed.
No.6 AWG.
Current changing constantly in magnitude and periodically in direction.

15. Operating coils - motors - transformers - relays and solenoids depend upon...
Derive a neutral for grounding purposes.
2000 watts
Kilovolt ampere (KVA).
Electro-magnetism for their operation.

16. AC voltage is raised or lowered by means of...
Transformers.
No.6 AWG.
200 volts AC.
A.C.

17. A transformer with a 1:1 ratio is usually a (an)...
Two speeds
Isolation transformer.
The motor rotation is reversed.
800 volts.

18. Which of the following does a squirrel cage induction motor have?
5:1
7 -630 volts.
Stator windings.
A device used to store electrical energy.

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

20. The primary leads of a single-phase transformer should be connected to the...
H terminals.
The sum of the two capacitors.
Disconnect the frame-grounding conductor.
Current that changes constantly in magnitude and periodically in direction.

21. 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.
277 volts.
Potential transformer.
An electrical shock hazard may exist.
5:1

22. The property of an electric circuit that opposes any change in current is called...
It provides good speed control.
Isolation transformer.
Inductance.
480 volts.

23. 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.
Capacitance.
Current changing constantly in magnitude and periodically in direction.
An electrical shock hazard may exist.

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...
Draw less current.
Short-circuited after power has been removed.
They must be installed at least 7 feet above the ground.
Zero amps.

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

26. Alternating current may be defined as...
3 -979 Volts.
Second-degree burn.
X.
Current that changes constantly in magnitude and periodically in direction.

27. A solenoid coil is...
60 Hertz
They must be installed at least 7 feet above the ground.
An electromagnet.
75 turns.

28. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Disconnect the frame-grounding conductor.
25 feet.
Stator windings.
12 to 15 times a minute.

29. All transformers step voltage up or down by...
7 -630 volts.
75 turns.
150 turns.
Inductance.

30. If any two-phase wires are reversed on a three-phase motor - the motor will...
An electrical shock hazard may exist.
Reverse its rotation.
100 volts.
200 volts AC.

31. A burn causing a blister is classified as a...
Inductance.
At the source transformer.
Second-degree burn.
15 feet off the ground.

32. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Reverse any two-phase leads.
Derive a neutral for grounding purposes.
60 cycles per second (60 Hertz).

33. The primary function of a power transformer is to provide...
The motor rotation is reversed.
Full-load - three-phase voltage.
A grounding resistor.
Draw less current.

34. The transformer used only to measure voltage is a...
Disconnect the frame-grounding conductor.
Potential transformer.
12 to 15 times a minute.
Squirrel-cage induction motor.

35. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Carotid pulse - which is located in the neck next to the Adam's apple.
At least two phases
The motor rotation is reversed.
200 volts AC.

36. The main function of CT's and PT's on a main substation is to...
Disconnect the frame-grounding conductor.
Allow for metering voltage and Current.
It provides good speed control.
Isolation transformer.

37. A wound-rotor induction motor has all the following EXCEPT...
Short-circuited after power has been removed.
Squirrel-cage rotor.
At the source transformer.
Cut around clothing that has adhered to the burned area.

38. The combined capacitance of two capacitors in parallel is...
3 -979 Volts.
The sum of the two capacitors.
Because less current flowing at high voltage causes less line loss per kilowatt.
150 turns.

39. What type motor is a wound-rotor induction motor?
Larger than that found in the primary winding.
A.C.
Reverse any two-phase leads.
7 -630 volts.

40. 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...
15 feet off the ground.
They should be made by the same manufacturer.
Tied together
100 volts.

41. Not true about AC power?
It provides good speed control.
150 turns.
7 -630 volts.
12 to 15 times a minute.

42. 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?
Transformer
Zero amps.
150 turns.
Disconnect the frame-grounding conductor.

43. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
An electromagnet.
Grounded phase and ground fault devices were not operating.
7 -630 volts.
600 volts.

44. What is the danger when working around capacitors?
Kilovolt ampere (KVA).
A.C.
The current will read zero.
An electrical shock hazard may exist.

45. To protect against over-current in a three-phase circuit over-current protection must be provided for...
75 turns.
A device used to store electrical energy.
At least two phases
1 amp.

46. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Kilovolt ampere (KVA).
Current changing constantly in magnitude and periodically in direction.
A step-up transformer.
Hyperventilation.

47. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
H terminals.
Hyperventilation.
The current will read zero.
100 turns.

48. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Allow for metering voltage and Current.
25 feet.
Disconnect the frame-grounding conductor.
The chest should rise or inflate.

49. Current transformers - or CT's - are used to...
25 feet.
The sum of the two capacitors.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Draw less current.

50. 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.C.
200 volts AC.
The motor rotation is reversed.
7 -630 volts.