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. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Transformer
Shunted and taped
Current that changes constantly in magnitude and periodically in direction.
15 feet off the ground.

2. 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.
A device used to store electrical energy.
5:1.
2000 watts
Electro-magnetism for their operation.

3. Where should grounding resistors be located?
100 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
At the source transformer.
Circuit Breaker.

4. 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.
Kilovolt ampere (KVA).
Full-load - three-phase voltage.
A grounding resistor.

5. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
The sum of the two capacitors.
A device used to store electrical energy.
Larger than that found in the primary winding.
A step-up transformer.

6. Three-phase AC underground cables must be provided with overcurrent protection using a...
H terminals.
Provides single-phase power to smaller loads such as lights - heaters - etc.
They must be installed at least 7 feet above the ground.
Circuit Breaker.

7. The property of an electric circuit that opposes any change in current is called...
H terminals.
Inductance.
Clamp-on ammeter.
100 volts.

8. A solenoid coil is...
2000 watts
An electromagnet.
Zero amps.
5:1

9. Not a symptom of electrical shock?.
The motor rotation is reversed.
At the source transformer.
Hyperventilation.
The current will read zero.

10. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
15 feet off the ground.
75 turns.
600 volts.

11. What is the first step to be followed in aiding a victim of electrical shock?
H terminals.
Check to make sure that the victim is not still in contact with the electricity.
Two speeds
5:1

12. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
800 volts.
Two speeds
277 volts.
Grounded phase and ground fault devices were not operating.

13. 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?
800 volts.
Disconnect the frame-grounding conductor.
3 -979 Volts.
Shunted and taped

14. What is the danger when working around capacitors?
An electrical shock hazard may exist.
Second-degree burn.
Tied together
Hyperventilation.

15. Not true about AC power?
An electromagnet.
It provides good speed control.
A device used to store electrical energy.
75 turns.

16. Define alternating current...
Inductance.
Draw less current.
Current changing constantly in magnitude and periodically in direction.
100 turns.

17. The primary leads of a single-phase transformer should be connected to the...
Grounded phase and ground fault devices were not operating.
H terminals.
Inductance.
100 volts.

18. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Inductance.
277 volts.
Nearly constant.
60 Hertz

19. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Cut around clothing that has adhered to the burned area.
480 volts.
No.6 AWG.
A step-up transformer.

20. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Draw less current.
Inductance.
Reverse any two-phase leads.
X.

21. AC voltage is raised or lowered by means of...
Shunted and taped
Transformers.
Clamp-on ammeter.
Potential transformer.

22. The purpose of a zig-zag transformer is to...
Nearly constant.
They must be installed at least 7 feet above the ground.
100 volts.
Derive a neutral for grounding purposes.

23. A burn causing a blister is classified as a...
They must be installed at least 7 feet above the ground.
Second-degree burn.
Clamp-on ammeter.
Reverse any two-phase leads.

24. If any two-phase wires are reversed on a three-phase motor - the motor will...
The chest should rise or inflate.
Larger than that found in the primary winding.
An electrical shock hazard may exist.
Reverse its rotation.

25. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Full-load - three-phase voltage.
200 volts AC.
At least two phases
The capacitors should be discharged.

26. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Full-load - three-phase voltage.
Disconnect the frame-grounding conductor.
Two speeds
Derive a neutral for grounding purposes.

27. All transformers step voltage up or down by...
Nearly constant.
At least two phases
Inductance.
5:1.

28. What type of 3-phase AC motor is used most often around a mine?
100 volts.
Squirrel-cage induction motor.
Tied together
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

29. High voltage is used to transmit power over long distances...
25 feet.
Continuous.
Because less current flowing at high voltage causes less line loss per kilowatt.
They must be installed at least 7 feet above the ground.

30. 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?
H terminals.
Transformers.
Stator windings.
150 turns.

31. Compared to the secondary of a loaded - step-down transformer - the primary has...
H terminals.
Lower current and higher voltage
Allow for metering voltage and Current.
75 turns.

32. The primary function of a power transformer is to provide...
Isolation transformer.
7 -630 volts.
Full-load - three-phase voltage.
Carotid pulse - which is located in the neck next to the Adam's apple.

33. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Because less current flowing at high voltage causes less line loss per kilowatt.
They should be made by the same manufacturer.
The motor rotation is reversed.
60 cycles per second (60 Hertz).

34. 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...
Draw less current.
Hyperventilation.
Cut around clothing that has adhered to the burned area.
Short-circuited after power has been removed.

35. What is a capacitor?
Inductance.
A.C.
A device used to store electrical energy.
Disconnect the frame-grounding conductor.

36. Alternating current may be defined as...
Derive a neutral for grounding purposes.
At least two phases
Grounded phase and ground fault devices were not operating.
Current that changes constantly in magnitude and periodically in direction.

37. The standard frequency of alternating current used at a mine is...
Cut around clothing that has adhered to the burned area.
The chest should rise or inflate.
60 Hertz
480 volts.

38. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Alternating current.
The capacitors should be discharged.
Clamp-on ammeter.
Draw less current.

39. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
Clamp-on ammeter.
Four times less than that of the secondary.
Alternating current.

40. 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.
A device used to store electrical energy.
Transformers.
5:1
Draw less current.

41. The main function of CT's and PT's on a main substation is to...
They should be made by the same manufacturer.
Allow for metering voltage and Current.
Check to make sure that the victim is not still in contact with the electricity.
Short-circuited after power has been removed.

42. The combined capacitance of two capacitors in parallel is...
12 to 15 times a minute.
Squirrel-cage rotor.
Nearly constant.
The sum of the two capacitors.

43. 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?
7 -630 volts.
It provides good speed control.
75 turns.
H terminals.

44. 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...
100 volts.
25 feet.
1 amp.
Electro-magnetism for their operation.

45. The property of an electrical circuit that opposes any change in voltage is called...
Full-load - three-phase voltage.
The sum of the two capacitors.
Current changing constantly in magnitude and periodically in direction.
Capacitance.

46. What should the duty rating of a grounding resistor be?
Two speeds
Kilovolt ampere (KVA).
Continuous.
Lower current and higher voltage.

47. When not connected to a load - the secondary leads of a current transformer should be...
Lower current and higher voltage
Shunted and taped
Transformers.
Inductance.

48. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Derive a neutral for grounding purposes.
Disconnect the frame-grounding conductor.
Draw less current.
2000 watts

49. The transformer used only to measure voltage is a...
200 volts AC.
Potential transformer.
It provides good speed control.
Circuit Breaker.

50. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
No.6 AWG.
1 amp.
An electrical shock hazard may exist.
Carotid pulse - which is located in the neck next to the Adam's apple.