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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. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Squirrel-cage induction motor.
Grounded phase and ground fault devices were not operating.
Continuous.

2. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Current changing constantly in magnitude and periodically in direction.
60 cycles per second (60 Hertz).
Four times less than that of the secondary.
Larger than that found in the primary winding.

3. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Reverse its rotation.
480 volts.
At least two phases
Derive a neutral for grounding purposes.

4. The secondary windings on a 10:1 step-down transformer will have a wire size...
Electro-magnetism for their operation.
Circuit Breaker.
480 volts.
Larger than that found in the primary winding.

5. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Current that changes constantly in magnitude and periodically in direction.
Transformers.
7 -630 volts.
Alternating current.

6. 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...
Zero amps.
480 volts.
Short-circuited after power has been removed.
Draw less current.

7. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Cut around clothing that has adhered to the burned area.
Larger than that found in the primary winding.
A grounding resistor.

8. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Squirrel-cage induction motor.
Tied together
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

9. 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?
No.6 AWG.
100 turns.
Nearly constant.
Four times less than that of the secondary.

10. The primary leads of a single-phase transformer should be connected to the...
2000 watts
12 to 15 times a minute.
H terminals.
150 turns.

11. Which of the following does a squirrel cage induction motor have?
Four times less than that of the secondary.
Capacitance.
7 -630 volts.
Stator windings.

12. 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.
Electro-magnetism for their operation.
It provides good speed control.
Current that changes constantly in magnitude and periodically in direction.

13. A burn causing a blister is classified as a...
Second-degree burn.
The current will read zero.
Transformer
Circuit Breaker.

14. Where should grounding resistors be located?
Because less current flowing at high voltage causes less line loss per kilowatt.
Kilovolt ampere (KVA).
At the source transformer.
X.

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?
Reverse its rotation.
Squirrel-cage induction motor.
They should be made by the same manufacturer.
200 volts AC.

16. Compared to the secondary of a loaded - step-down transformer - the primary has...
Potential transformer.
Lower current and higher voltage.
Larger than that found in the primary winding.
The chest should rise or inflate.

17. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
They must be installed at least 7 feet above the ground.
7 -630 volts.
Zero amps.

18. The speed of an alternating current - squirrel-cage induction motor is...
Lower current and higher voltage
Nearly constant.
1 amp.
5:1

19. The size of a transformer is measured in...
Kilovolt ampere (KVA).
Circuit Breaker.
2000 watts
Four times less than that of the secondary.

20. All transformers step voltage up or down by...
Tied together
Transformers.
Reverse its rotation.
Inductance.

21. What should the duty rating of a grounding resistor be?
480 volts.
277 volts.
Continuous.
15 feet off the ground.

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

23. At what rate should mouth-to-mouth resuscitation be applied?
The capacitors should be discharged.
12 to 15 times a minute.
Potential transformer.
X.

24. 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...
Circuit Breaker.
Tied together
Hyperventilation.
Squirrel-cage rotor.

25. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
It provides good speed control.
An electrical shock hazard may exist.
Because less current flowing at high voltage causes less line loss per kilowatt.

26. Not an acceptable method for the installations of surface transformers?
Transformer
They must be installed at least 7 feet above the ground.
Zero amps.
Derive a neutral for grounding purposes.

27. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Hyperventilation.
5:1
100 volts.

28. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
150 turns.
Two speeds
Current changing constantly in magnitude and periodically in direction.

29. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Grounded phase and ground fault devices were not operating.
The capacitors should be discharged.
Inductance.
1 amp.

30. The primary function of a power transformer is to provide...
The chest should rise or inflate.
Full-load - three-phase voltage.
A.C.
15 feet off the ground.

31. If any two-phase wires are reversed on a three-phase motor - the motor will...
Allow for metering voltage and Current.
Reverse its rotation.
7 -630 volts.
Transformers.

32. Not a symptom of electrical shock?.
480 volts.
Reverse any two-phase leads.
H terminals.
Hyperventilation.

33. What is a capacitor?
A device used to store electrical energy.
Cut around clothing that has adhered to the burned area.
Four times less than that of the secondary.
Current changing constantly in magnitude and periodically in direction.

34. 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.
Potential transformer.
5:1.
Grounded phase and ground fault devices were not operating.
Current that changes constantly in magnitude and periodically in direction.

35. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Grounded phase and ground fault devices were not operating.
150 turns.
Potential transformer.
Current that changes constantly in magnitude and periodically in direction.

36. What type of 3-phase AC motor is used most often around a mine?
Hyperventilation.
At least two phases
Short-circuited after power has been removed.
Squirrel-cage induction motor.

37. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
They must be installed at least 7 feet above the ground.
Larger than that found in the primary winding.
Continuous.
The motor rotation is reversed.

38. A wound-rotor induction motor has all the following EXCEPT...
H terminals.
Squirrel-cage rotor.
5:1
Larger than that found in the primary winding.

39. A solenoid coil is...
25 feet.
7 -630 volts.
Capacitance.
An electromagnet.

40. Current in an AC circuit may be measured by...
Draw less current.
Reverse its rotation.
Clamp-on ammeter.
60 cycles per second (60 Hertz).

41. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
1 amp.
Alternating current.
Larger than that found in the primary winding.
Zero amps.

42. 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?
7 -630 volts.
They must be installed at least 7 feet above the ground.
15 feet off the ground.
800 volts.

43. 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?
15 feet off the ground.
Reverse any two-phase leads.
Current changing constantly in magnitude and periodically in direction.
3 -979 Volts.

44. Not true about AC power?
Disconnect the frame-grounding conductor.
Four times less than that of the secondary.
480 volts.
It provides good speed control.

45. 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.
800 volts.
Reverse any two-phase leads.
A grounding resistor.
5:1

46. The transformer used only to measure voltage is a...
Second-degree burn.
The current will read zero.
150 turns.
Potential transformer.

47. When not connected to a load - the secondary leads of a current transformer should be...
Short-circuited after power has been removed.
Derive a neutral for grounding purposes.
Shunted and taped
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

48. How should clothing be removed from a burn?
Hyperventilation.
The sum of the two capacitors.
Cut around clothing that has adhered to the burned area.
100 volts.

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?
480 volts.
Squirrel-cage induction motor.
75 turns.
Circuit Breaker.

50. 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...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Inductance.
They must be installed at least 7 feet above the ground.
100 volts.