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. What is a capacitor?
100 volts.
A device used to store electrical energy.
Current changing constantly in magnitude and periodically in direction.
1 amp.

2. The combined capacitance of two capacitors in parallel is...
It provides good speed control.
Larger than that found in the primary winding.
The sum of the two capacitors.
Isolation transformer.

3. 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.
5:1.
Current changing constantly in magnitude and periodically in direction.
Potential transformer.

4. 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.
Inductance.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

5. The main function of CT's and PT's on a main substation is to...
Grounded phase and ground fault devices were not operating.
They must be installed at least 7 feet above the ground.
Allow for metering voltage and Current.
60 Hertz

6. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
An electrical shock hazard may exist.
A.C.
X.
Cut around clothing that has adhered to the burned area.

7. 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?
Provides single-phase power to smaller loads such as lights - heaters - etc.
75 turns.
12 to 15 times a minute.
3 -979 Volts.

8. At what rate should mouth-to-mouth resuscitation be applied?
Potential transformer.
12 to 15 times a minute.
1 amp.
They must be installed at least 7 feet above the ground.

9. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
3 -979 Volts.
Hyperventilation.
600 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

10. The property of an electric circuit that opposes any change in current is called...
600 volts.
Inductance.
Circuit Breaker.
H terminals.

11. A transformer with a 1:1 ratio is usually a (an)...
Cut around clothing that has adhered to the burned area.
Kilovolt ampere (KVA).
100 volts.
Isolation transformer.

12. The secondary windings on a 10:1 step-down transformer will have a wire size...
The motor rotation is reversed.
Larger than that found in the primary winding.
The capacitors should be discharged.
5:1.

13. Compared to the secondary of a loaded - step-down transformer - the primary has...
150 turns.
Check to make sure that the victim is not still in contact with the electricity.
Lower current and higher voltage
Circuit Breaker.

14. 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?
3 -979 Volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
Circuit Breaker.
100 turns.

15. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Circuit Breaker.
Two speeds
No.6 AWG.
Transformer

16. Alternating current may be defined as...
7 -630 volts.
Current that changes constantly in magnitude and periodically in direction.
The sum of the two capacitors.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

17. 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...
A.C.
Larger than that found in the primary winding.
2000 watts
100 volts.

18. What should the duty rating of a grounding resistor be?
15 feet off the ground.
Continuous.
Second-degree burn.
Two speeds

19. When not connected to a load - the secondary leads of a current transformer should be...
Derive a neutral for grounding purposes.
They must be installed at least 7 feet above the ground.
Transformer
Shunted and taped

20. Not a symptom of electrical shock?.
5:1
Draw less current.
Hyperventilation.
The capacitors should be discharged.

21. 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?
3 -979 Volts.
H terminals.
Carotid pulse - which is located in the neck next to the Adam's apple.
75 turns.

22. 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...
No.6 AWG.
Grounded phase and ground fault devices were not operating.
Draw less current.
5:1.

23. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Draw less current.
Clamp-on ammeter.
Four times less than that of the secondary.
An electrical shock hazard may exist.

24. Current transformers - or CT's - are used to...
100 turns.
Draw less current.
Two speeds
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

25. Operating coils - motors - transformers - relays and solenoids depend upon...
Nearly constant.
Electro-magnetism for their operation.
Potential transformer.
Full-load - three-phase voltage.

26. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
800 volts.
It provides good speed control.
A device used to store electrical energy.

27. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Draw less current.
Cut around clothing that has adhered to the burned area.
60 cycles per second (60 Hertz).

28. What steps up or steps down AC voltage?
Lower current and higher voltage.
Transformer
Draw less current.
Derive a neutral for grounding purposes.

29. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
3 -979 Volts.
Two speeds
2000 watts
Because less current flowing at high voltage causes less line loss per kilowatt.

30. What type motor is a wound-rotor induction motor?
A.C.
Two speeds
Because less current flowing at high voltage causes less line loss per kilowatt.
Draw less current.

31. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
Inductance.
Squirrel-cage induction motor.
800 volts.

32. 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.
75 turns.
Grounded phase and ground fault devices were not operating.
An electrical shock hazard may exist.

33. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Isolation transformer.
Disconnect the frame-grounding conductor.
600 volts.
They should be made by the same manufacturer.

34. Current that changes periodically in direction is...
60 Hertz
Alternating current.
A step-up transformer.
1 amp.

35. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
Derive a neutral for grounding purposes.
Isolation transformer.
Transformer

36. 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.
Derive a neutral for grounding purposes.
5:1.
Short-circuited after power has been removed.

37. The primary leads of a single-phase transformer should be connected to the...
Provides single-phase power to smaller loads such as lights - heaters - etc.
H terminals.
Inductance.
Cut around clothing that has adhered to the burned area.

38. A control power transformer...
Clamp-on ammeter.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Kilovolt ampere (KVA).
Grounded phase and ground fault devices were not operating.

39. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Lower current and higher voltage.
5:1.
Check to make sure that the victim is not still in contact with the electricity.

40. Where should grounding resistors be located?
Cut around clothing that has adhered to the burned area.
Reverse its rotation.
200 volts AC.
At the source transformer.

41. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Continuous.
Reverse any two-phase leads.
Zero amps.
Transformers.

42. 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.
3 -979 Volts.
No.6 AWG.
H terminals.

43. 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?
100 volts.
Reverse any two-phase leads.
75 turns.
7 -630 volts.

44. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
They should be made by the same manufacturer.
Disconnect the frame-grounding conductor.
Squirrel-cage rotor.
60 cycles per second (60 Hertz).

45. What type of 3-phase AC motor is used most often around a mine?
A.C.
Squirrel-cage induction motor.
Current changing constantly in magnitude and periodically in direction.
277 volts.

46. Define alternating current...
Kilovolt ampere (KVA).
Provides single-phase power to smaller loads such as lights - heaters - etc.
They must be installed at least 7 feet above the ground.
Current changing constantly in magnitude and periodically in direction.

47. A solenoid coil is...
At the source transformer.
Allow for metering voltage and Current.
An electromagnet.
Hyperventilation.

48. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
Four times less than that of the secondary.
Two speeds
Current that changes constantly in magnitude and periodically in direction.

49. The standard frequency of alternating current used at a mine is...
60 Hertz
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
600 volts.
The chest should rise or inflate.

50. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Kilovolt ampere (KVA).
Carotid pulse - which is located in the neck next to the Adam's apple.
Reverse any two-phase leads.