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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 property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
277 volts.
75 turns.
Shunted and taped

2. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Transformer
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
They should be made by the same manufacturer.
Second-degree burn.

3. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Allow for metering voltage and Current.
Two speeds
480 volts.
A.C.

4. Not a symptom of electrical shock?.
Circuit Breaker.
Capacitance.
25 feet.
Hyperventilation.

5. When not connected to a load - the secondary leads of a current transformer should be...
Clamp-on ammeter.
An electromagnet.
Shunted and taped
Larger than that found in the primary winding.

6. 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.
Stator windings.
3 -979 Volts.
Squirrel-cage induction motor.

7. 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...
Allow for metering voltage and Current.
Draw less current.
Transformer
A.C.

8. If any two-phase wires are reversed on a three-phase motor - the motor will...
Current changing constantly in magnitude and periodically in direction.
Reverse its rotation.
Reverse any two-phase leads.
5:1

9. The property of an electric circuit that opposes any change in current is called...
Cut around clothing that has adhered to the burned area.
Inductance.
X.
75 turns.

10. What should the duty rating of a grounding resistor be?
Potential transformer.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
A step-up transformer.
Continuous.

11. 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...
Tied together
H terminals.
Draw less current.
The chest should rise or inflate.

12. 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?
5:1.
An electrical shock hazard may exist.
3 -979 Volts.
277 volts.

13. 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?
The motor rotation is reversed.
75 turns.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
480 volts.

14. Compared to the secondary of a loaded - step-down transformer - the primary has...
Shunted and taped
Full-load - three-phase voltage.
Lower current and higher voltage.
The chest should rise or inflate.

15. What type of 3-phase AC motor is used most often around a mine?
1 amp.
It provides good speed control.
Short-circuited after power has been removed.
Squirrel-cage induction motor.

16. 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.
150 turns.
Grounded phase and ground fault devices were not operating.
Alternating current.

17. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Inductance.
2000 watts
Kilovolt ampere (KVA).
Potential transformer.

18. 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.
Lower current and higher voltage
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
5:1.
2000 watts

19. The secondary windings on a 10:1 step-down transformer will have a wire size...
5:1
The chest should rise or inflate.
Larger than that found in the primary winding.
Four times less than that of the secondary.

20. 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?
Second-degree burn.
Zero amps.
100 turns.
150 turns.

21. Where should grounding resistors be located?
At the source transformer.
Draw less current.
25 feet.
Current that changes constantly in magnitude and periodically in direction.

22. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
Reverse its rotation.
Lower current and higher voltage.
15 feet off the ground.

23. What steps up or steps down AC voltage?
Draw less current.
X.
Isolation transformer.
Transformer

24. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
It provides good speed control.
Reverse any two-phase leads.
1 amp.
12 to 15 times a minute.

25. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Cut around clothing that has adhered to the burned area.
A step-up transformer.
H terminals.
The sum of the two capacitors.

26. Current in an AC circuit may be measured by...
Clamp-on ammeter.
60 cycles per second (60 Hertz).
Isolation transformer.
Tied together

27. All transformers step voltage up or down by...
Check to make sure that the victim is not still in contact with the electricity.
Continuous.
Inductance.
Short-circuited after power has been removed.

28. 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.
7 -630 volts.
Reverse any two-phase leads.
Check to make sure that the victim is not still in contact with the electricity.

29. 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?
Short-circuited after power has been removed.
600 volts.
7 -630 volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.

30. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Transformer
The motor rotation is reversed.
200 volts AC.
The chest should rise or inflate.

31. 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?
An electromagnet.
Tied together
75 turns.
H terminals.

32. What is the danger when working around capacitors?
Isolation transformer.
They should be made by the same manufacturer.
An electrical shock hazard may exist.
Derive a neutral for grounding purposes.

33. The purpose of a zig-zag transformer is to...
Cut around clothing that has adhered to the burned area.
Continuous.
Derive a neutral for grounding purposes.
The capacitors should be discharged.

34. Compared to the secondary of a loaded - step-down transformer - the primary has...
Cut around clothing that has adhered to the burned area.
A step-up transformer.
Lower current and higher voltage
600 volts.

35. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Second-degree burn.
60 cycles per second (60 Hertz).
Capacitance.
No.6 AWG.

36. Which of the following does a squirrel cage induction motor have?
At least two phases
Electro-magnetism for their operation.
60 Hertz
Stator windings.

37. High voltage is used to transmit power over long distances...
Kilovolt ampere (KVA).
Provides single-phase power to smaller loads such as lights - heaters - etc.
Because less current flowing at high voltage causes less line loss per kilowatt.
X.

38. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
An electromagnet.
Full-load - three-phase voltage.
The current will read zero.

39. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
The chest should rise or inflate.
Short-circuited after power has been removed.
Zero amps.
Stator windings.

40. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Because less current flowing at high voltage causes less line loss per kilowatt.
They should be made by the same manufacturer.
A grounding resistor.
100 turns.

41. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Short-circuited after power has been removed.
Grounded phase and ground fault devices were not operating.
An electromagnet.

42. The primary function of a power transformer is to provide...
2000 watts
Carotid pulse - which is located in the neck next to the Adam's apple.
Full-load - three-phase voltage.
The current will read zero.

43. The combined capacitance of two capacitors in parallel is...
Larger than that found in the primary winding.
The sum of the two capacitors.
An electromagnet.
Draw less current.

44. The main function of CT's and PT's on a main substation is to...
Shunted and taped
Squirrel-cage rotor.
Allow for metering voltage and Current.
Squirrel-cage induction motor.

45. 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...
The chest should rise or inflate.
200 volts AC.
Draw less current.
Nearly constant.

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.
3 -979 Volts.
25 feet.
The sum of the two capacitors.

47. Not an acceptable method for the installations of surface transformers?
Carotid pulse - which is located in the neck next to the Adam's apple.
Capacitance.
They must be installed at least 7 feet above the ground.
60 cycles per second (60 Hertz).

48. A control power transformer...
7 -630 volts.
Electro-magnetism for their operation.
Because less current flowing at high voltage causes less line loss per kilowatt.
Provides single-phase power to smaller loads such as lights - heaters - etc.

49. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
X.
A device used to store electrical energy.
The capacitors should be discharged.
Tied together

50. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Electro-magnetism for their operation.
A.C.
Reverse any two-phase leads.