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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. The size of a transformer is measured in...
They must be installed at least 7 feet above the ground.
Squirrel-cage induction motor.
No.6 AWG.
Kilovolt ampere (KVA).

2. Not true about AC power?
It provides good speed control.
A grounding resistor.
75 turns.
Larger than that found in the primary winding.

3. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
25 feet.
200 volts AC.
Two speeds

4. What is the danger when working around capacitors?
Continuous.
An electrical shock hazard may exist.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
3 -979 Volts.

5. How do you change the direction of a 3-phase AC motor?
75 turns.
Potential transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Reverse any two-phase leads.

6. A transformer with a 1:1 ratio is usually a (an)...
Hyperventilation.
Squirrel-cage induction motor.
A grounding resistor.
Isolation transformer.

7. What is the first step to be followed in aiding a victim of electrical shock?
Shunted and taped
Check to make sure that the victim is not still in contact with the electricity.
At least two phases
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

8. 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?
75 turns.
Transformers.
Inductance.
200 volts AC.

9. The purpose of a zig-zag transformer is to...
Four times less than that of the secondary.
5:1.
Derive a neutral for grounding purposes.
Two speeds

10. Define alternating current...
Circuit Breaker.
277 volts.
Current changing constantly in magnitude and periodically in direction.
Tied together

11. 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.
Continuous.
Lower current and higher voltage
Reverse any two-phase leads.

12. A wound-rotor induction motor has all the following EXCEPT...
75 turns.
Squirrel-cage rotor.
The sum of the two capacitors.
60 cycles per second (60 Hertz).

13. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Draw less current.
X.
The chest should rise or inflate.
Cut around clothing that has adhered to the burned area.

14. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Grounded phase and ground fault devices were not operating.
Transformer
At least two phases
Draw less current.

15. 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?
Check to make sure that the victim is not still in contact with the electricity.
Draw less current.
X.
200 volts AC.

16. 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?
Zero amps.
600 volts.
Disconnect the frame-grounding conductor.
100 turns.

17. 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...
Potential transformer.
Tied together
Squirrel-cage induction motor.
Draw less current.

18. Three-phase AC underground cables must be provided with overcurrent protection using a...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Circuit Breaker.
Electro-magnetism for their operation.
Inductance.

19. 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...
Because less current flowing at high voltage causes less line loss per kilowatt.
Draw less current.
They must be installed at least 7 feet above the ground.
5:1.

20. Compared to the secondary of a loaded - step-down transformer - the primary has...
Check to make sure that the victim is not still in contact with the electricity.
Lower current and higher voltage.
Transformers.
At the source transformer.

21. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Disconnect the frame-grounding conductor.
Second-degree burn.
1 amp.

22. When not connected to a load - the secondary leads of a current transformer should be...
Two speeds
Shunted and taped
150 turns.
Full-load - three-phase voltage.

23. If any two-phase wires are reversed on a three-phase motor - the motor will...
Second-degree burn.
They must be installed at least 7 feet above the ground.
Reverse its rotation.
25 feet.

24. A solenoid coil is...
An electromagnet.
Continuous.
They must be installed at least 7 feet above the ground.
480 volts.

25. The secondary windings on a 10:1 step-down transformer will have a wire size...
60 cycles per second (60 Hertz).
Larger than that found in the primary winding.
Stator windings.
Because less current flowing at high voltage causes less line loss per kilowatt.

26. Operating coils - motors - transformers - relays and solenoids depend upon...
Tied together
Electro-magnetism for their operation.
Squirrel-cage rotor.
Larger than that found in the primary winding.

27. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
480 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
277 volts.
Draw less current.

28. Current that changes periodically in direction is...
The capacitors should be discharged.
Carotid pulse - which is located in the neck next to the Adam's apple.
A step-up transformer.
Alternating current.

29. 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...
Stator windings.
Lower current and higher voltage
25 feet.
Draw less current.

30. The standard frequency of power supplied by the power company is...
Inductance.
The motor rotation is reversed.
Inductance.
60 cycles per second (60 Hertz).

31. 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.
Cut around clothing that has adhered to the burned area.
Grounded phase and ground fault devices were not operating.
5:1.
Inductance.

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

33. What should the duty rating of a grounding resistor be?
Inductance.
Current changing constantly in magnitude and periodically in direction.
75 turns.
Continuous.

34. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
A grounding resistor.
Lower current and higher voltage.
Shunted and taped
No.6 AWG.

35. High voltage is used to transmit power over long distances...
1 amp.
60 cycles per second (60 Hertz).
Current that changes constantly in magnitude and periodically in direction.
Because less current flowing at high voltage causes less line loss per kilowatt.

36. 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...
Disconnect the frame-grounding conductor.
Zero amps.
Cut around clothing that has adhered to the burned area.
100 volts.

37. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Larger than that found in the primary winding.
Squirrel-cage induction motor.
At least two phases
The motor rotation is reversed.

38. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
60 cycles per second (60 Hertz).
X.
The chest should rise or inflate.

39. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
15 feet off the ground.
1 amp.
The sum of the two capacitors.
7 -630 volts.

40. The combined capacitance of two capacitors in parallel is...
2000 watts
The sum of the two capacitors.
25 feet.
60 Hertz

41. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
150 turns.
Alternating current.
Zero amps.

42. The transformer used only to measure voltage is a...
The capacitors should be discharged.
Potential transformer.
H terminals.
The motor rotation is reversed.

43. The property of an electrical circuit that opposes any change in voltage is called...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
5:1.
Capacitance.
Potential transformer.

44. AC voltage is raised or lowered by means of...
Inductance.
Allow for metering voltage and Current.
Transformers.
Capacitance.

45. 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.
800 volts.
The sum of the two capacitors.
Current that changes constantly in magnitude and periodically in direction.

46. 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?
Zero amps.
Draw less current.
800 volts.
480 volts.

47. The primary function of a power transformer is to provide...
It provides good speed control.
Full-load - three-phase voltage.
1 amp.
Kilovolt ampere (KVA).

48. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Clamp-on ammeter.
600 volts.
480 volts.
Potential transformer.

49. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Short-circuited after power has been removed.
A step-up transformer.
The capacitors should be discharged.
Draw less current.

50. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
277 volts.
Two speeds
Potential transformer.
1 amp.