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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 following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
Reverse any two-phase leads.
Inductance.
The current will read zero.

2. A burn causing a blister is classified as a...
Alternating current.
Second-degree burn.
The motor rotation is reversed.
Squirrel-cage induction motor.

3. The size of a transformer is measured in...
It provides good speed control.
Kilovolt ampere (KVA).
277 volts.
Circuit Breaker.

4. The secondary windings on a 10:1 step-down transformer will have a wire size...
Derive a neutral for grounding purposes.
25 feet.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Larger than that found in the primary winding.

5. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Allow for metering voltage and Current.
Inductance.
1 amp.

6. If any two-phase wires are reversed on a three-phase motor - the motor will...
Transformers.
Reverse its rotation.
At least two phases
It provides good speed control.

7. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
1 amp.
7 -630 volts.
25 feet.
Disconnect the frame-grounding conductor.

8. 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?
Kilovolt ampere (KVA).
Potential transformer.
5:1
3 -979 Volts.

9. The transformer used only to measure voltage is a...
The current will read zero.
Larger than that found in the primary winding.
Transformers.
Potential transformer.

10. 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.
At least two phases
12 to 15 times a minute.
277 volts.

11. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
The motor rotation is reversed.
Short-circuited after power has been removed.
Provides single-phase power to smaller loads such as lights - heaters - etc.
A grounding resistor.

12. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
60 cycles per second (60 Hertz).
5:1.
Continuous.
No.6 AWG.

13. The purpose of a zig-zag transformer is to...
Full-load - three-phase voltage.
Shunted and taped
Derive a neutral for grounding purposes.
Potential transformer.

14. What is a capacitor?
Provides single-phase power to smaller loads such as lights - heaters - etc.
A device used to store electrical energy.
Clamp-on ammeter.
Four times less than that of the secondary.

15. 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.
Tied together
H terminals.
25 feet.

16. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
7 -630 volts.
Zero amps.
Stator windings.
Nearly constant.

17. What steps up or steps down AC voltage?
Transformer
The motor rotation is reversed.
Current changing constantly in magnitude and periodically in direction.
Check to make sure that the victim is not still in contact with the electricity.

18. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Carotid pulse - which is located in the neck next to the Adam's apple.
Two speeds
Disconnect the frame-grounding conductor.

19. Not true about AC power?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Squirrel-cage induction motor.
It provides good speed control.
Reverse any two-phase leads.

20. 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.
Second-degree burn.
100 turns.
800 volts.

21. 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.
Four times less than that of the secondary.
Squirrel-cage induction motor.
5:1
The chest should rise or inflate.

22. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
A grounding resistor.
100 turns.
An electromagnet.

23. 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?
Larger than that found in the primary winding.
200 volts AC.
Electro-magnetism for their operation.
Transformers.

24. 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?
Circuit Breaker.
The current will read zero.
800 volts.
480 volts.

25. 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?
Reverse its rotation.
150 turns.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Reverse any two-phase leads.

26. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A grounding resistor.
60 Hertz
The motor rotation is reversed.
Check to make sure that the victim is not still in contact with the electricity.

27. Operating coils - motors - transformers - relays and solenoids depend upon...
Tied together
Zero amps.
Electro-magnetism for their operation.
Potential transformer.

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

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29. 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.
75 turns.
Derive a neutral for grounding purposes.
5:1.
7 -630 volts.

30. A transformer with a 1:1 ratio is usually a (an)...
Reverse any two-phase leads.
Isolation transformer.
They must be installed at least 7 feet above the ground.
No.6 AWG.

31. 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?
2000 watts
Check to make sure that the victim is not still in contact with the electricity.
An electromagnet.
100 turns.

32. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
The current will read zero.
Grounded phase and ground fault devices were not operating.
They should be made by the same manufacturer.
800 volts.

33. Compared to the secondary of a loaded - step-down transformer - the primary has...
Tied together
It provides good speed control.
Transformer
Lower current and higher voltage.

34. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Two speeds
A step-up transformer.
The sum of the two capacitors.
Allow for metering voltage and Current.

35. Define alternating current...
Squirrel-cage induction motor.
277 volts.
Current changing constantly in magnitude and periodically in direction.
The sum of the two capacitors.

36. The main function of CT's and PT's on a main substation is to...
25 feet.
Allow for metering voltage and Current.
Lower current and higher voltage
Nearly constant.

37. 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?
600 volts.
5:1
X.
Inductance.

38. 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?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Lower current and higher voltage.
Stator windings.
75 turns.

39. What type of 3-phase AC motor is used most often around a mine?
Transformers.
Squirrel-cage induction motor.
Allow for metering voltage and Current.
200 volts AC.

40. 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...
7 -630 volts.
100 volts.
Zero amps.
150 turns.

41. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
The chest should rise or inflate.
Current that changes constantly in magnitude and periodically in direction.
At least two phases

42. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Second-degree burn.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Alternating current.

43. What type motor is a wound-rotor induction motor?
Alternating current.
A.C.
12 to 15 times a minute.
Grounded phase and ground fault devices were not operating.

44. At what rate should mouth-to-mouth resuscitation be applied?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The motor rotation is reversed.
The capacitors should be discharged.
12 to 15 times a minute.

45. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Disconnect the frame-grounding conductor.
An electrical shock hazard may exist.
Grounded phase and ground fault devices were not operating.
An electromagnet.

46. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
60 Hertz
Continuous.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Full-load - three-phase voltage.

47. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
Reverse its rotation.
5:1.
Four times less than that of the secondary.

48. How do you change the direction of a 3-phase AC motor?
Provides single-phase power to smaller loads such as lights - heaters - etc.
Kilovolt ampere (KVA).
Grounded phase and ground fault devices were not operating.
Reverse any two-phase leads.

49. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Tied together
Draw less current.
An electromagnet.
7 -630 volts.

50. Where should grounding resistors be located?
At the source transformer.
Second-degree burn.
60 Hertz
A.C.