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. Not a symptom of electrical shock?.
Inductance.
Hyperventilation.
Disconnect the frame-grounding conductor.
Squirrel-cage induction motor.

2. A control power transformer...
Continuous.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Current changing constantly in magnitude and periodically in direction.
100 turns.

3. 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...
Transformers.
Four times less than that of the secondary.
Zero amps.
Draw less current.

4. What is a capacitor?
Short-circuited after power has been removed.
Current changing constantly in magnitude and periodically in direction.
Hyperventilation.
A device used to store electrical energy.

5. The property of an electric circuit that opposes any change in current is called...
Second-degree burn.
The sum of the two capacitors.
Inductance.
Current that changes constantly in magnitude and periodically in direction.

6. The primary function of a power transformer is to provide...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
75 turns.
A device used to store electrical energy.
Full-load - three-phase voltage.

7. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Capacitance.
They should be made by the same manufacturer.
2000 watts
Shunted and taped

8. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
At least two phases
600 volts.
Lower current and higher voltage.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

9. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
A device used to store electrical energy.
At least two phases
Cut around clothing that has adhered to the burned area.

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...
Current that changes constantly in magnitude and periodically in direction.
Tied together
480 volts.
Short-circuited after power has been removed.

11. Which of the following does a squirrel cage induction motor have?
5:1
1 amp.
Stator windings.
60 Hertz

12. 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?
100 volts.
100 turns.
Electro-magnetism for their operation.
Grounded phase and ground fault devices were not operating.

13. What should the duty rating of a grounding resistor be?
Full-load - three-phase voltage.
A.C.
Squirrel-cage induction motor.
Continuous.

14. The combined capacitance of two capacitors in parallel is...
277 volts.
An electrical shock hazard may exist.
The sum of the two capacitors.
480 volts.

15. The standard frequency of alternating current used at a mine is...
2000 watts
60 Hertz
An electromagnet.
150 turns.

16. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Current that changes constantly in magnitude and periodically in direction.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The motor rotation is reversed.
H terminals.

17. The purpose of a zig-zag transformer is to...
Carotid pulse - which is located in the neck next to the Adam's apple.
Current that changes constantly in magnitude and periodically in direction.
Derive a neutral for grounding purposes.
Provides single-phase power to smaller loads such as lights - heaters - etc.

18. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
The sum of the two capacitors.
Capacitance.
3 -979 Volts.

19. A transformer has 2000 turns in the primary and 500 turns in the secondary. The primary voltage is 3 -200 volts. What is the secondary voltage?
Full-load - three-phase voltage.
At the source transformer.
480 volts.
800 volts.

20. 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...
Shunted and taped
Capacitance.
Short-circuited after power has been removed.
Draw less current.

21. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Squirrel-cage induction motor.
Four times less than that of the secondary.
At least two phases
Continuous.

22. 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.
Continuous.
5:1.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
15 feet off the ground.

23. The primary leads of a single-phase transformer should be connected to the...
H terminals.
3 -979 Volts.
7 -630 volts.
60 Hertz

24. 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.
Kilovolt ampere (KVA).
They must be installed at least 7 feet above the ground.
Transformers.

25. A burn causing a blister is classified as a...
Second-degree burn.
2000 watts
Zero amps.
They must be installed at least 7 feet above the ground.

26. A transformer has 1 -600 turns in the primary and 400 turns in the secondary. The primary voltage is 2 -400 volts. What is the secondary voltage?
The capacitors should be discharged.
Isolation transformer.
600 volts.
Circuit Breaker.

27. Not true about AC power?
An electromagnet.
It provides good speed control.
At the source transformer.
Transformer

28. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Potential transformer.
At least two phases
Disconnect the frame-grounding conductor.
Allow for metering voltage and Current.

29. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Second-degree burn.
X.
15 feet off the ground.
Provides single-phase power to smaller loads such as lights - heaters - etc.

30. The transformer used only to measure voltage is a...
Potential transformer.
Squirrel-cage rotor.
Cut around clothing that has adhered to the burned area.
Stator windings.

31. 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?
At the source transformer.
They must be installed at least 7 feet above the ground.
3 -979 Volts.
Hyperventilation.

32. AC voltage is raised or lowered by means of...
5:1.
2000 watts
Transformers.
5:1

33. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
12 to 15 times a minute.
5:1.
277 volts.
5:1

34. When not connected to a load - the secondary leads of a current transformer should be...
An electrical shock hazard may exist.
Current changing constantly in magnitude and periodically in direction.
Electro-magnetism for their operation.
Shunted and taped

35. What type motor is a wound-rotor induction motor?
A.C.
The capacitors should be discharged.
Larger than that found in the primary winding.
Current that changes constantly in magnitude and periodically in direction.

36. A wound-rotor induction motor has all the following EXCEPT...
An electromagnet.
Squirrel-cage rotor.
Allow for metering voltage and Current.
Four times less than that of the secondary.

37. The standard frequency of power supplied by the power company is...
The current will read zero.
Stator windings.
A grounding resistor.
60 cycles per second (60 Hertz).

38. A transformer with a 1:1 ratio is usually a (an)...
Circuit Breaker.
Isolation transformer.
Full-load - three-phase voltage.
Grounded phase and ground fault devices were not operating.

39. Current that changes periodically in direction is...
800 volts.
The capacitors should be discharged.
Current that changes constantly in magnitude and periodically in direction.
Alternating current.

40. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Provides single-phase power to smaller loads such as lights - heaters - etc.
A grounding resistor.
Current changing constantly in magnitude and periodically in direction.
At the source transformer.

41. At what rate should mouth-to-mouth resuscitation be applied?
5:1
800 volts.
12 to 15 times a minute.
Stator windings.

42. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
A grounding resistor.
5:1
Lower current and higher voltage

43. Where should grounding resistors be located?
Draw less current.
Derive a neutral for grounding purposes.
Full-load - three-phase voltage.
At the source transformer.

44. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Stator windings.
Squirrel-cage rotor.
Short-circuited after power has been removed.

45. What is the first step to be followed in aiding a victim of electrical shock?
Draw less current.
Check to make sure that the victim is not still in contact with the electricity.
Continuous.
Grounded phase and ground fault devices were not operating.

46. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Electro-magnetism for their operation.
Squirrel-cage rotor.
Capacitance.

47. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
They must be installed at least 7 feet above the ground.
7 -630 volts.
No.6 AWG.
25 feet.

48. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
The current will read zero.
277 volts.
Two speeds
The sum of the two capacitors.

49. 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.
They must be installed at least 7 feet above the ground.
Stator windings.
Grounded phase and ground fault devices were not operating.

50. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
800 volts.
It provides good speed control.
Potential transformer.