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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. Current in an AC circuit may be measured by...
A step-up transformer.
75 turns.
Clamp-on ammeter.
The motor rotation is reversed.

2. The standard frequency of power supplied by the power company is...
Zero amps.
60 cycles per second (60 Hertz).
Alternating current.
Second-degree burn.

3. Where should grounding resistors be located?
At the source transformer.
Check to make sure that the victim is not still in contact with the electricity.
Because less current flowing at high voltage causes less line loss per kilowatt.
Electro-magnetism for their operation.

4. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The capacitors should be discharged.
Disconnect the frame-grounding conductor.
Short-circuited after power has been removed.
The motor rotation is reversed.

5. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Two speeds
Reverse any two-phase leads.
A grounding resistor.
Tied together

6. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
The chest should rise or inflate.
2000 watts
100 turns.
No.6 AWG.

7. A wound-rotor induction motor has all the following EXCEPT...
100 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Squirrel-cage rotor.
480 volts.

8. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Check to make sure that the victim is not still in contact with the electricity.
They should be made by the same manufacturer.
Zero amps.

9. 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?
480 volts.
150 turns.
Alternating current.
25 feet.

10. What type motor is a wound-rotor induction motor?
600 volts.
100 turns.
Inductance.
A.C.

11. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
100 turns.
No.6 AWG.
Current changing constantly in magnitude and periodically in direction.
150 turns.

12. 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 electrical shock hazard may exist.
H terminals.
75 turns.
The sum of the two capacitors.

13. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
Squirrel-cage rotor.
277 volts.
Alternating current.

14. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Second-degree burn.
A step-up transformer.
600 volts.
The current will read zero.

15. 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.
Squirrel-cage rotor.
H terminals.
An electromagnet.

16. High voltage is used to transmit power over long distances...
Reverse any two-phase leads.
200 volts AC.
600 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.

17. Not an acceptable method for the installations of surface transformers?
25 feet.
The motor rotation is reversed.
At least two phases
They must be installed at least 7 feet above the ground.

18. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Squirrel-cage induction motor.
Because less current flowing at high voltage causes less line loss per kilowatt.
The capacitors should be discharged.
Draw less current.

19. All transformers step voltage up or down by...
Inductance.
A grounding resistor.
Lower current and higher voltage
Two speeds

20. 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.
800 volts.
480 volts.
Draw less current.

21. 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...
Draw less current.
Inductance.
Continuous.
X.

22. Not true about AC power?
A step-up transformer.
It provides good speed control.
The sum of the two capacitors.
At least two phases

23. What is the danger when working around capacitors?
At least two phases
5:1
At the source transformer.
An electrical shock hazard may exist.

24. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Squirrel-cage rotor.
25 feet.
Zero amps.
Stator windings.

25. 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?
Squirrel-cage rotor.
480 volts.
Draw less current.
800 volts.

26. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
5:1.
Lower current and higher voltage.
Squirrel-cage rotor.
The chest should rise or inflate.

27. The property of an electric circuit that opposes any change in current is called...
100 volts.
H terminals.
Inductance.
It provides good speed control.

28. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Check to make sure that the victim is not still in contact with the electricity.
At least two phases
Grounded phase and ground fault devices were not operating.
Allow for metering voltage and Current.

29. The combined capacitance of two capacitors in parallel is...
5:1
60 Hertz
600 volts.
The sum of the two capacitors.

30. 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?
Isolation transformer.
Draw less current.
100 turns.
3 -979 Volts.

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

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32. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Reverse any two-phase leads.
X.
Disconnect the frame-grounding conductor.
Two speeds

33. Current that changes periodically in direction is...
Alternating current.
H terminals.
Short-circuited after power has been removed.
Kilovolt ampere (KVA).

34. The primary function of a power transformer is to provide...
Inductance.
5:1
150 turns.
Full-load - three-phase voltage.

35. At what rate should mouth-to-mouth resuscitation be applied?
Zero amps.
They must be installed at least 7 feet above the ground.
Squirrel-cage induction motor.
12 to 15 times a minute.

36. What steps up or steps down AC voltage?
No.6 AWG.
Transformer
Zero amps.
Carotid pulse - which is located in the neck next to the Adam's apple.

37. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
1 amp.
Draw less current.
Squirrel-cage rotor.

38. 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.
Grounded phase and ground fault devices were not operating.
Squirrel-cage rotor.
Circuit Breaker.

39. 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...
12 to 15 times a minute.
Isolation transformer.
Draw less current.
100 volts.

40. The standard frequency of alternating current used at a mine is...
60 Hertz
75 turns.
At least two phases
2000 watts

41. Not a symptom of electrical shock?.
60 cycles per second (60 Hertz).
1 amp.
100 turns.
Hyperventilation.

42. The speed of an alternating current - squirrel-cage induction motor is...
They must be installed at least 7 feet above the ground.
25 feet.
Squirrel-cage rotor.
Nearly constant.

43. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Current changing constantly in magnitude and periodically in direction.
The capacitors should be discharged.
7 -630 volts.
2000 watts

44. 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
The chest should rise or inflate.
At least two phases
Cut around clothing that has adhered to the burned area.

45. Operating coils - motors - transformers - relays and solenoids depend upon...
Lower current and higher voltage.
Electro-magnetism for their operation.
Continuous.
Derive a neutral for grounding purposes.

46. The size of a transformer is measured in...
5:1.
Kilovolt ampere (KVA).
3 -979 Volts.
Capacitance.

47. 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.
7 -630 volts.
Clamp-on ammeter.
Draw less current.

48. 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.
Nearly constant.
5:1
Current that changes constantly in magnitude and periodically in direction.
2000 watts

49. 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?
75 turns.
No.6 AWG.
Continuous.
60 Hertz

50. The main function of CT's and PT's on a main substation is to...
Inductance.
Allow for metering voltage and Current.
Squirrel-cage induction motor.
Clamp-on ammeter.