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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. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
Check to make sure that the victim is not still in contact with the electricity.
Reverse its rotation.
The motor rotation is reversed.

2. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Kilovolt ampere (KVA).
Two speeds
At least two phases
60 Hertz

3. The standard frequency of power supplied by the power company is...
Short-circuited after power has been removed.
277 volts.
60 cycles per second (60 Hertz).
Cut around clothing that has adhered to the burned area.

4. The standard frequency of alternating current used at a mine is...
The motor rotation is reversed.
60 Hertz
480 volts.
X.

5. What type of 3-phase AC motor is used most often around a mine?
Circuit Breaker.
Squirrel-cage induction motor.
Tied together
Grounded phase and ground fault devices were not operating.

6. What is the danger when working around capacitors?
An electrical shock hazard may exist.
Disconnect the frame-grounding conductor.
The chest should rise or inflate.
Reverse any two-phase leads.

7. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
12 to 15 times a minute.
Current that changes constantly in magnitude and periodically in direction.
No.6 AWG.
A grounding resistor.

8. The secondary windings on a 10:1 step-down transformer will have a wire size...
Two speeds
Larger than that found in the primary winding.
5:1
Reverse any two-phase leads.

9. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
2000 watts
Grounded phase and ground fault devices were not operating.
Squirrel-cage rotor.
Provides single-phase power to smaller loads such as lights - heaters - etc.

10. The speed of an alternating current - squirrel-cage induction motor is...
Larger than that found in the primary winding.
100 volts.
Nearly constant.
Alternating current.

11. A control power transformer...
Tied together
Provides single-phase power to smaller loads such as lights - heaters - etc.
They must be installed at least 7 feet above the ground.
Four times less than that of the secondary.

12. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
H terminals.
12 to 15 times a minute.
The motor rotation is reversed.
A step-up transformer.

13. 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.
Grounded phase and ground fault devices were not operating.
5:1.
Carotid pulse - which is located in the neck next to the Adam's apple.
The capacitors should be discharged.

14. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
They should be made by the same manufacturer.
X.
12 to 15 times a minute.

15. 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.
800 volts.
Current changing constantly in magnitude and periodically in direction.
150 turns.

16. The combined capacitance of two capacitors in parallel is...
The chest should rise or inflate.
200 volts AC.
The sum of the two capacitors.
At the source transformer.

17. 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?
800 volts.
150 turns.
Because less current flowing at high voltage causes less line loss per kilowatt.
1 amp.

18. To protect against over-current in a three-phase circuit over-current protection must be provided for...
It provides good speed control.
Four times less than that of the secondary.
At least two phases
Squirrel-cage rotor.

19. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
The sum of the two capacitors.
Circuit Breaker.
Alternating current.

20. The purpose of a zig-zag transformer is to...
Alternating current.
Derive a neutral for grounding purposes.
The chest should rise or inflate.
At the source transformer.

21. The transformer used only to measure voltage is a...
Disconnect the frame-grounding conductor.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Potential transformer.
15 feet off the ground.

22. The primary function of a power transformer is to provide...
Squirrel-cage rotor.
Full-load - three-phase voltage.
Disconnect the frame-grounding conductor.
Nearly constant.

23. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
Disconnect the frame-grounding conductor.
Stator windings.
480 volts.

24. What is a capacitor?
A device used to store electrical energy.
Second-degree burn.
Lower current and higher voltage.
200 volts AC.

25. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
The chest should rise or inflate.
Draw less current.
The sum of the two capacitors.

26. Where should grounding resistors be located?
Inductance.
Continuous.
At the source transformer.
Clamp-on ammeter.

27. A transformer with a 1:1 ratio is usually a (an)...
The chest should rise or inflate.
Isolation transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.
2000 watts

28. 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?
Because less current flowing at high voltage causes less line loss per kilowatt.
100 turns.
Kilovolt ampere (KVA).
Squirrel-cage rotor.

29. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
A grounding resistor.
Continuous.
They must be installed at least 7 feet above the ground.
1 amp.

30. A burn causing a blister is classified as a...
12 to 15 times a minute.
Second-degree burn.
An electrical shock hazard may exist.
Zero amps.

31. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Draw less current.
277 volts.
Grounded phase and ground fault devices were not operating.
Provides single-phase power to smaller loads such as lights - heaters - etc.

32. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
H terminals.
5:1
X.
Allow for metering voltage and Current.

33. 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.
100 turns.
Nearly constant.
Lower current and higher voltage

34. How do you change the direction of a 3-phase AC motor?
Current changing constantly in magnitude and periodically in direction.
600 volts.
Reverse any two-phase leads.
X.

35. 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.
Draw less current.
An electrical shock hazard may exist.
Zero amps.

36. 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?
Cut around clothing that has adhered to the burned area.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
They must be installed at least 7 feet above the ground.
75 turns.

37. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
100 volts.
Capacitance.
The motor rotation is reversed.
Squirrel-cage rotor.

38. A solenoid coil is...
Draw less current.
An electromagnet.
Cut around clothing that has adhered to the burned area.
Two speeds

39. Not an acceptable method for the installations of surface transformers?
7 -630 volts.
A step-up transformer.
They must be installed at least 7 feet above the ground.
Check to make sure that the victim is not still in contact with the electricity.

40. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
7 -630 volts.
An electrical shock hazard may exist.
25 feet.
The current will read zero.

41. 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.
5:1
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The chest should rise or inflate.
H terminals.

42. Compared to the secondary of a loaded - step-down transformer - the primary has...
Inductance.
Draw less current.
At least two phases
Lower current and higher voltage

43. What steps up or steps down AC voltage?
60 cycles per second (60 Hertz).
Transformers.
1 amp.
Transformer

44. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
Squirrel-cage rotor.
Squirrel-cage induction motor.
277 volts.

45. High voltage is used to transmit power over long distances...
75 turns.
Current that changes constantly in magnitude and periodically in direction.
The sum of the two capacitors.
Because less current flowing at high voltage causes less line loss per kilowatt.

46. 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?
Alternating current.
600 volts.
Current that changes constantly in magnitude and periodically in direction.
Kilovolt ampere (KVA).

47. 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.
A step-up transformer.
At least two phases
An electrical shock hazard may exist.

48. 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.
60 cycles per second (60 Hertz).
100 volts.
1 amp.

49. If any two-phase wires are reversed on a three-phase motor - the motor will...
Transformers.
Cut around clothing that has adhered to the burned area.
No.6 AWG.
Reverse its rotation.

50. Which of the following does a squirrel cage induction motor have?
Stator windings.
7 -630 volts.
Short-circuited after power has been removed.
Two speeds