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AC Theory

Instructions:

Answer 50 questions in 15 minutes.
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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 following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
An electromagnet.
They should be made by the same manufacturer.
75 turns.

2. The standard frequency of alternating current used at a mine is...
It provides good speed control.
Grounded phase and ground fault devices were not operating.
60 Hertz
25 feet.

3. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
A step-up transformer.
2000 watts
Zero amps.

4. What steps up or steps down AC voltage?
3 -979 Volts.
Transformer
600 volts.
Hyperventilation.

5. What type motor is a wound-rotor induction motor?
75 turns.
Nearly constant.
A.C.
150 turns.

6. 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...
Nearly constant.
Carotid pulse - which is located in the neck next to the Adam's apple.
Second-degree burn.
100 volts.

7. Alternating current may be defined as...
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.
Transformer
Potential transformer.

8. When not connected to a load - the secondary leads of a current transformer should be...
2000 watts
Inductance.
Shunted and taped
A device used to store electrical energy.

9. Which of the following does a squirrel cage induction motor have?
Transformer
Isolation transformer.
A grounding resistor.
Stator windings.

10. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Derive a neutral for grounding purposes.
Reverse any two-phase leads.
Four times less than that of the secondary.
A grounding resistor.

11. A transformer with a 1:1 ratio is usually a (an)...
Shunted and taped
Check to make sure that the victim is not still in contact with the electricity.
7 -630 volts.
Isolation transformer.

12. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Stator windings.
3 -979 Volts.
Squirrel-cage induction motor.

13. The size of a transformer is measured in...
They should be made by the same manufacturer.
Cut around clothing that has adhered to the burned area.
Kilovolt ampere (KVA).
A step-up transformer.

14. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Grounded phase and ground fault devices were not operating.
H terminals.
The capacitors should be discharged.

15. 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?
200 volts AC.
480 volts.
Continuous.
3 -979 Volts.

16. All transformers step voltage up or down by...
3 -979 Volts.
Inductance.
5:1.
Isolation transformer.

17. 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.
Derive a neutral for grounding purposes.
Cut around clothing that has adhered to the burned area.
Electro-magnetism for their operation.
5:1.

18. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Inductance.
Capacitance.
7 -630 volts.
The chest should rise or inflate.

19. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Current changing constantly in magnitude and periodically in direction.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Alternating current.

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...
A.C.
Draw less current.
Allow for metering voltage and Current.
Tied together

21. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Provides single-phase power to smaller loads such as lights - heaters - etc.
277 volts.
Transformer
At least two phases

22. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Two speeds
Larger than that found in the primary winding.
The capacitors should be discharged.
Hyperventilation.

23. Operating coils - motors - transformers - relays and solenoids depend upon...
5:1
Electro-magnetism for their operation.
Squirrel-cage rotor.
Hyperventilation.

24. The primary leads of a single-phase transformer should be connected to the...
H terminals.
Four times less than that of the secondary.
Allow for metering voltage and Current.
1 amp.

25. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
Nearly constant.
75 turns.
Squirrel-cage rotor.

26. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Current changing constantly in magnitude and periodically in direction.
800 volts.
The motor rotation is reversed.
Kilovolt ampere (KVA).

27. A solenoid coil is...
At least two phases
An electromagnet.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The motor rotation is reversed.

28. A burn causing a blister is classified as a...
600 volts.
Current that changes constantly in magnitude and periodically in direction.
Second-degree burn.
480 volts.

29. 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?
Inductance.
600 volts.
100 turns.
The motor rotation is reversed.

30. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Circuit Breaker.
H terminals.
Full-load - three-phase voltage.

31. 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.
Cut around clothing that has adhered to the burned area.
277 volts.
5:1
Isolation transformer.

32. Define alternating current...
Two speeds
Continuous.
480 volts.
Current changing constantly in magnitude and periodically in direction.

33. 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?
Draw less current.
800 volts.
Four times less than that of the secondary.
Larger than that found in the primary winding.

34. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Shunted and taped
100 turns.
3 -979 Volts.

35. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Short-circuited after power has been removed.
5:1
Carotid pulse - which is located in the neck next to the Adam's apple.
They must be installed at least 7 feet above the ground.

36. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
A grounding resistor.
Lower current and higher voltage
Second-degree burn.

37. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
75 turns.
Hyperventilation.
Grounded phase and ground fault devices were not operating.

38. The primary function of a power transformer is to provide...
The capacitors should be discharged.
Alternating current.
Draw less current.
Full-load - three-phase voltage.

39. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The sum of the two capacitors.
The current will read zero.
They must be installed at least 7 feet above the ground.
Circuit Breaker.

40. High voltage is used to transmit power over long distances...
At the source transformer.
Four times less than that of the secondary.
Because less current flowing at high voltage causes less line loss per kilowatt.
75 turns.

41. Current that changes periodically in direction is...
Alternating current.
Squirrel-cage induction motor.
Check to make sure that the victim is not still in contact with the electricity.
100 turns.

42. 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?
12 to 15 times a minute.
600 volts.
Two speeds
Squirrel-cage induction motor.

43. Current transformers - or CT's - are used to...
Clamp-on ammeter.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Continuous.
12 to 15 times a minute.

44. A transformer with 3000 turns in the primary winding has a primary voltage of 4 -800 volts and a secondary voltage of 240 volts. How many turns are in the secondary winding?
X.
Cut around clothing that has adhered to the burned area.
100 volts.
150 turns.

45. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Circuit Breaker.
X.
At least two phases
Larger than that found in the primary winding.

46. What is the danger when working around capacitors?
A device used to store electrical energy.
An electrical shock hazard may exist.
25 feet.
60 cycles per second (60 Hertz).

47. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Continuous.
1 amp.
Capacitance.
Transformer

48. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Reverse its rotation.
The capacitors should be discharged.
100 volts.
A step-up transformer.

49. How should clothing be removed from a burn?
Potential transformer.
At the source transformer.
Two speeds
Cut around clothing that has adhered to the burned area.

50. The property of an electric circuit that opposes any change in current is called...
No.6 AWG.
Inductance.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Hyperventilation.

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AC Theory

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