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. All transformers step voltage up or down by...
Squirrel-cage induction motor.
277 volts.
Inductance.
200 volts AC.

2. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Shunted and taped
Short-circuited after power has been removed.
Larger than that found in the primary winding.
The motor rotation is reversed.

3. The size of a transformer is measured in...
Kilovolt ampere (KVA).
100 turns.
600 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.

4. 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?
Hyperventilation.
Reverse any two-phase leads.
200 volts AC.
At the source transformer.

5. Compared to the secondary of a loaded - step-down transformer - the primary has...
The motor rotation is reversed.
Lower current and higher voltage.
Transformer
Grounded phase and ground fault devices were not operating.

6. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Draw less current.
A grounding resistor.
3 -979 Volts.
Circuit Breaker.

7. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Zero amps.
They should be made by the same manufacturer.
Full-load - three-phase voltage.
Lower current and higher voltage.

8. What steps up or steps down AC voltage?
The motor rotation is reversed.
Transformer
5:1.
Squirrel-cage induction motor.

9. The transformer used only to measure voltage is a...
277 volts.
100 volts.
Lower current and higher voltage
Potential transformer.

10. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
Squirrel-cage induction motor.
5:1
They should be made by the same manufacturer.

11. A control power transformer...
Disconnect the frame-grounding conductor.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Second-degree burn.
At least two phases

12. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Carotid pulse - which is located in the neck next to the Adam's apple.
2000 watts
Draw less current.
800 volts.

13. AC voltage is raised or lowered by means of...
The chest should rise or inflate.
They should be made by the same manufacturer.
Transformers.
Derive a neutral for grounding purposes.

14. Not true about AC power?
Four times less than that of the secondary.
Tied together
Current changing constantly in magnitude and periodically in direction.
It provides good speed control.

15. 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.
5:1.
Tied together
Check to make sure that the victim is not still in contact with the electricity.

16. What type of 3-phase AC motor is used most often around a mine?
Carotid pulse - which is located in the neck next to the Adam's apple.
Larger than that found in the primary winding.
Four times less than that of the secondary.
Squirrel-cage induction motor.

17. When not connected to a load - the secondary leads of a current transformer should be...
Allow for metering voltage and Current.
They must be installed at least 7 feet above the ground.
Shunted and taped
Grounded phase and ground fault devices were not operating.

18. 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?
2000 watts
60 cycles per second (60 Hertz).
The sum of the two capacitors.
75 turns.

19. Current in an AC circuit may be measured by...
Stator windings.
Clamp-on ammeter.
Tied together
60 Hertz

20. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Draw less current.
Four times less than that of the secondary.
Lower current and higher voltage
Grounded phase and ground fault devices were not operating.

21. Not a symptom of electrical shock?.
Inductance.
At the source transformer.
480 volts.
Hyperventilation.

22. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
A device used to store electrical energy.
Transformer
12 to 15 times a minute.

23. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Full-load - three-phase voltage.
Alternating current.
Current that changes constantly in magnitude and periodically in direction.
No.6 AWG.

24. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Transformers.
Derive a neutral for grounding purposes.
Current that changes constantly in magnitude and periodically in direction.
Zero amps.

25. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The current will read zero.
The motor rotation is reversed.
Inductance.
Four times less than that of the secondary.

26. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
Squirrel-cage induction motor.
Inductance.
5:1.

27. Three-phase AC underground cables must be provided with overcurrent protection using a...
Current that changes constantly in magnitude and periodically in direction.
Squirrel-cage rotor.
The motor rotation is reversed.
Circuit Breaker.

28. What should the duty rating of a grounding resistor be?
Continuous.
The sum of the two capacitors.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Grounded phase and ground fault devices were not operating.

29. Where should grounding resistors be located?
5:1.
At the source transformer.
Hyperventilation.
Capacitance.

30. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
2000 watts
X.
Derive a neutral for grounding purposes.

31. A solenoid coil is...
At least two phases
An electromagnet.
Carotid pulse - which is located in the neck next to the Adam's apple.
75 turns.

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...
5:1
Draw less current.
7 -630 volts.
No.6 AWG.

33. 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.
277 volts.
Circuit Breaker.
Because less current flowing at high voltage causes less line loss per kilowatt.

34. The primary leads of a single-phase transformer should be connected to the...
Zero amps.
Reverse any two-phase leads.
H terminals.
Inductance.

35. 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.
Nearly constant.
600 volts.
Lower current and higher voltage.

36. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Larger than that found in the primary winding.
The sum of the two capacitors.
Kilovolt ampere (KVA).
Two speeds

37. The combined capacitance of two capacitors in parallel is...
277 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
No.6 AWG.
The sum of the two capacitors.

38. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Continuous.
Four times less than that of the secondary.
Circuit Breaker.
They should be made by the same manufacturer.

39. The property of an electrical circuit that opposes any change in voltage is called...
100 turns.
Nearly constant.
No.6 AWG.
Capacitance.

40. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
15 feet off the ground.
Potential transformer.
Transformer

41. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Lower current and higher voltage
A step-up transformer.
Disconnect the frame-grounding conductor.
Continuous.

42. The primary function of a power transformer is to provide...
Current changing constantly in magnitude and periodically in direction.
Because less current flowing at high voltage causes less line loss per kilowatt.
Kilovolt ampere (KVA).
Full-load - three-phase voltage.

43. The purpose of a zig-zag transformer is to...
Draw less current.
Reverse any two-phase leads.
Derive a neutral for grounding purposes.
Check to make sure that the victim is not still in contact with the electricity.

44. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Potential transformer.
An electromagnet.
Stator windings.

45. The property of an electric circuit that opposes any change in current is called...
Inductance.
Tied together
277 volts.
No.6 AWG.

46. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Potential transformer.
H terminals.
Reverse any two-phase leads.

47. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Continuous.
1 amp.
Full-load - three-phase voltage.
They should be made by the same manufacturer.

48. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
The capacitors should be discharged.
Current that changes constantly in magnitude and periodically in direction.
100 turns.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

49. If any two-phase wires are reversed on a three-phase motor - the motor will...
100 volts.
Current changing constantly in magnitude and periodically in direction.
An electrical shock hazard may exist.
Reverse its rotation.

50. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
Reverse any two-phase leads.
Current that changes constantly in magnitude and periodically in direction.
Current changing constantly in magnitude and periodically in direction.