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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 type of 3-phase AC motor is used most often around a mine?
Provides single-phase power to smaller loads such as lights - heaters - etc.
Clamp-on ammeter.
Squirrel-cage induction motor.
Reverse its rotation.

2. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
The current will read zero.
Reverse its rotation.
15 feet off the ground.
A device used to store electrical energy.

3. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Alternating current.
277 volts.
Squirrel-cage rotor.
The capacitors should be discharged.

4. What steps up or steps down AC voltage?
Clamp-on ammeter.
25 feet.
60 cycles per second (60 Hertz).
Transformer

5. 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?
600 volts.
7 -630 volts.
Potential transformer.
Inductance.

6. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Electro-magnetism for their operation.
Squirrel-cage rotor.
It provides good speed control.
A grounding resistor.

7. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Four times less than that of the secondary.
Derive a neutral for grounding purposes.
Draw less current.
Provides single-phase power to smaller loads such as lights - heaters - etc.

8. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
No.6 AWG.
Four times less than that of the secondary.
At least two phases

9. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Reverse any two-phase leads.
150 turns.
They should be made by the same manufacturer.
Second-degree burn.

10. Which of the following does a squirrel cage induction motor have?
Stator windings.
Nearly constant.
X.
600 volts.

11. 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 turns.
Nearly constant.
200 volts AC.
100 volts.

12. To protect against over-current in a three-phase circuit over-current protection must be provided for...
An electrical shock hazard may exist.
200 volts AC.
Larger than that found in the primary winding.
At least two phases

13. The standard frequency of power supplied by the power company is...
Reverse any two-phase leads.
60 cycles per second (60 Hertz).
No.6 AWG.
Stator windings.

14. The combined capacitance of two capacitors in parallel is...
Derive a neutral for grounding purposes.
They must be installed at least 7 feet above the ground.
The sum of the two capacitors.
Current that changes constantly in magnitude and periodically in direction.

15. 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...
200 volts AC.
H terminals.
Isolation transformer.
Draw less current.

16. Current that changes periodically in direction is...
No.6 AWG.
Lower current and higher voltage
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Alternating current.

17. What type motor is a wound-rotor induction motor?
A.C.
Isolation transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.
An electromagnet.

18. How do you change the direction of a 3-phase AC motor?
Circuit Breaker.
150 turns.
Reverse any two-phase leads.
Four times less than that of the secondary.

19. The primary leads of a single-phase transformer should be connected to the...
An electromagnet.
H terminals.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Squirrel-cage rotor.

20. How should clothing be removed from a burn?
Provides single-phase power to smaller loads such as lights - heaters - etc.
X.
The motor rotation is reversed.
Cut around clothing that has adhered to the burned area.

21. AC voltage is raised or lowered by means of...
Inductance.
Transformers.
A step-up transformer.
3 -979 Volts.

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

23. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
Kilovolt ampere (KVA).
Squirrel-cage induction motor.
15 feet off the ground.

24. 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...
7 -630 volts.
Draw less current.
75 turns.
Cut around clothing that has adhered to the burned area.

25. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
2000 watts
Grounded phase and ground fault devices were not operating.
Circuit Breaker.
150 turns.

26. What is the first step to be followed in aiding a victim of electrical shock?
Check to make sure that the victim is not still in contact with the electricity.
Four times less than that of the secondary.
They should be made by the same manufacturer.
Stator windings.

27. 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?
Carotid pulse - which is located in the neck next to the Adam's apple.
75 turns.
60 Hertz
Lower current and higher voltage.

28. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
A.C.
Carotid pulse - which is located in the neck next to the Adam's apple.
12 to 15 times a minute.

29. Compared to the secondary of a loaded - step-down transformer - the primary has...
Two speeds
Full-load - three-phase voltage.
Transformer
Lower current and higher voltage.

30. All transformers step voltage up or down by...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
H terminals.
Inductance.
5:1

31. 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?
Short-circuited after power has been removed.
200 volts AC.
60 cycles per second (60 Hertz).
They should be made by the same manufacturer.

32. 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...
60 cycles per second (60 Hertz).
600 volts.
A.C.
Tied together

33. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Derive a neutral for grounding purposes.
Draw less current.
Shunted and taped
Zero amps.

34. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
60 Hertz
Disconnect the frame-grounding conductor.
75 turns.
A device used to store electrical energy.

35. Alternating current may be defined as...
Continuous.
H terminals.
600 volts.
Current that changes constantly in magnitude and periodically in direction.

36. Current transformers - or CT's - are used to...
2000 watts
Second-degree burn.
Grounded phase and ground fault devices were not operating.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

37. 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.
Capacitance.
7 -630 volts.
Full-load - three-phase voltage.
5:1

38. Where should grounding resistors be located?
The capacitors should be discharged.
600 volts.
At the source transformer.
A device used to store electrical energy.

39. The size of a transformer is measured in...
Kilovolt ampere (KVA).
Inductance.
An electromagnet.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

40. What is a capacitor?
A device used to store electrical energy.
800 volts.
H terminals.
Shunted and taped

41. 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?
800 volts.
Check to make sure that the victim is not still in contact with the electricity.
60 cycles per second (60 Hertz).
Draw less current.

42. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Transformers.
75 turns.
Continuous.

43. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Stator windings.
The current will read zero.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
2000 watts

44. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
7 -630 volts.
100 turns.
1 amp.
100 volts.

45. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
A.C.
Cut around clothing that has adhered to the burned area.
Full-load - three-phase voltage.

46. The transformer used only to measure voltage is a...
800 volts.
Transformer
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Potential transformer.

47. The property of an electric circuit that opposes any change in current is called...
Clamp-on ammeter.
The motor rotation is reversed.
Inductance.
The current will read zero.

48. A burn causing a blister is classified as a...
Second-degree burn.
Two speeds
An electrical shock hazard may exist.
Current changing constantly in magnitude and periodically in direction.

49. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Continuous.
Two speeds
No.6 AWG.
Reverse any two-phase leads.

50. A wound-rotor induction motor has all the following EXCEPT...
Clamp-on ammeter.
Lower current and higher voltage.
Stator windings.
Squirrel-cage rotor.