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 you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Reverse any two-phase leads.
The capacitors should be discharged.
Grounded phase and ground fault devices were not operating.
The current will read zero.

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

3. 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?
A device used to store electrical energy.
Draw less current.
75 turns.
7 -630 volts.

4. The size of a transformer is measured in...
They should be made by the same manufacturer.
Derive a neutral for grounding purposes.
480 volts.
Kilovolt ampere (KVA).

5. The purpose of a zig-zag transformer is to...
X.
7 -630 volts.
Disconnect the frame-grounding conductor.
Derive a neutral for grounding purposes.

6. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Nearly constant.
3 -979 Volts.
277 volts.
Four times less than that of the secondary.

7. The property of an electrical circuit that opposes any change in voltage is called...
Squirrel-cage induction motor.
Capacitance.
60 Hertz
Kilovolt ampere (KVA).

8. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Inductance.
Continuous.
A.C.
1 amp.

9. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
15 feet off the ground.
Because less current flowing at high voltage causes less line loss per kilowatt.
Inductance.
Short-circuited after power has been removed.

10. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
5:1
75 turns.
Electro-magnetism for their operation.
Grounded phase and ground fault devices were not operating.

11. What steps up or steps down AC voltage?
Transformer
At least two phases
Circuit Breaker.
Reverse its rotation.

12. To protect against over-current in a three-phase circuit over-current protection must be provided for...
75 turns.
Current that changes constantly in magnitude and periodically in direction.
At least two phases
Capacitance.

13. The primary function of a power transformer is to provide...
At least two phases
Full-load - three-phase voltage.
150 turns.
277 volts.

14. The standard frequency of alternating current used at a mine is...
60 Hertz
Transformers.
The motor rotation is reversed.
Lower current and higher voltage.

15. All transformers step voltage up or down by...
Inductance.
Disconnect the frame-grounding conductor.
Hyperventilation.
A.C.

16. A transformer with a 1:1 ratio is usually a (an)...
Full-load - three-phase voltage.
Isolation transformer.
Stator windings.
Reverse its rotation.

17. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
Lower current and higher voltage
Cut around clothing that has adhered to the burned area.
277 volts.

18. A burn causing a blister is classified as a...
The sum of the two capacitors.
7 -630 volts.
Cut around clothing that has adhered to the burned area.
Second-degree burn.

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

20. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Nearly constant.
A grounding resistor.
An electromagnet.
3 -979 Volts.

21. Operating coils - motors - transformers - relays and solenoids depend upon...
At the source transformer.
Electro-magnetism for their operation.
An electrical shock hazard may exist.
150 turns.

22. What is a capacitor?
Check to make sure that the victim is not still in contact with the electricity.
A device used to store electrical energy.
5:1
Alternating current.

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?
75 turns.
25 feet.
200 volts AC.
Alternating current.

24. 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?
Second-degree burn.
100 turns.
Squirrel-cage induction motor.
An electromagnet.

25. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
H terminals.
No.6 AWG.
Check to make sure that the victim is not still in contact with the electricity.

26. 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...
800 volts.
A step-up transformer.
Tied together
Continuous.

27. What is the danger when working around capacitors?
25 feet.
An electrical shock hazard may exist.
No.6 AWG.
Carotid pulse - which is located in the neck next to the Adam's apple.

28. How do you change the direction of a 3-phase AC motor?
150 turns.
Reverse any two-phase leads.
The chest should rise or inflate.
Zero amps.

29. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
It provides good speed control.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Squirrel-cage induction motor.

30. The main function of CT's and PT's on a main substation is to...
Second-degree burn.
Allow for metering voltage and Current.
The sum of the two capacitors.
Shunted and taped

31. If any two-phase wires are reversed on a three-phase motor - the motor will...
2000 watts
Reverse its rotation.
60 Hertz
Reverse any two-phase leads.

32. What is the first step to be followed in aiding a victim of electrical shock?
100 turns.
Check to make sure that the victim is not still in contact with the electricity.
Clamp-on ammeter.
Electro-magnetism for their operation.

33. Not true about AC power?
Nearly constant.
It provides good speed control.
Derive a neutral for grounding purposes.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

34. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Provides single-phase power to smaller loads such as lights - heaters - etc.
At the source transformer.
2000 watts
Derive a neutral for grounding purposes.

35. 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.
Larger than that found in the primary winding.
An electrical shock hazard may exist.
A grounding resistor.
5:1.

36. The property of an electric circuit that opposes any change in current is called...
No.6 AWG.
Draw less current.
Inductance.
2000 watts

37. When not connected to a load - the secondary leads of a current transformer should be...
Check to make sure that the victim is not still in contact with the electricity.
Draw less current.
Shunted and taped
Allow for metering voltage and Current.

38. Which of the following does a squirrel cage induction motor have?
At least two phases
Stator windings.
Disconnect the frame-grounding conductor.
An electrical shock hazard may exist.

39. What type of 3-phase AC motor is used most often around a mine?
At least two phases
Squirrel-cage induction motor.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Isolation transformer.

40. 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?
150 turns.
Reverse any two-phase leads.
Circuit Breaker.
X.

41. The primary leads of a single-phase transformer should be connected to the...
Current changing constantly in magnitude and periodically in direction.
H terminals.
Stator windings.
Nearly constant.

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.
Clamp-on ammeter.
5:1
An electrical shock hazard may exist.
Tied together

43. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
It provides good speed control.
The capacitors should be discharged.
Isolation transformer.
Disconnect the frame-grounding conductor.

44. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
H terminals.
480 volts.
They should be made by the same manufacturer.
The motor rotation is reversed.

45. Three-phase AC underground cables must be provided with overcurrent protection using a...
A step-up transformer.
The chest should rise or inflate.
Circuit Breaker.
200 volts AC.

46. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
7 -630 volts.
480 volts.
Two speeds
Draw less current.

47. The combined capacitance of two capacitors in parallel is...
Current changing constantly in magnitude and periodically in direction.
X.
The sum of the two capacitors.
Larger than that found in the primary winding.

48. At what rate should mouth-to-mouth resuscitation be applied?
200 volts AC.
Zero amps.
Two speeds
12 to 15 times a minute.

49. High voltage is used to transmit power over long distances...
Carotid pulse - which is located in the neck next to the Adam's apple.
Isolation transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.
5:1

50. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
They must be installed at least 7 feet above the ground.
2000 watts
The current will read zero.