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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. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
Disconnect the frame-grounding conductor.
Short-circuited after power has been removed.
Two speeds

2. Define alternating current...
12 to 15 times a minute.
Current changing constantly in magnitude and periodically in direction.
100 turns.
Inductance.

3. Compared to the secondary of a loaded - step-down transformer - the primary has...
Reverse its rotation.
Lower current and higher voltage
X.
Transformer

4. A solenoid coil is...
An electromagnet.
Second-degree burn.
5:1.
5:1

5. A burn causing a blister is classified as a...
Second-degree burn.
Shunted and taped
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Electro-magnetism for their operation.

6. 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
Tied together
Full-load - three-phase voltage.
Circuit Breaker.

7. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
An electromagnet.
25 feet.
Alternating current.
The chest should rise or inflate.

8. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Two speeds
Because less current flowing at high voltage causes less line loss per kilowatt.
They should be made by the same manufacturer.
100 turns.

9. 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.
Short-circuited after power has been removed.
Current that changes constantly in magnitude and periodically in direction.
An electromagnet.

10. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
The motor rotation is reversed.
Reverse its rotation.
It provides good speed control.

11. 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.
Lower current and higher voltage
Circuit Breaker.

12. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
No.6 AWG.
It provides good speed control.
Draw less current.

13. How should clothing be removed from a burn?
Circuit Breaker.
An electromagnet.
Cut around clothing that has adhered to the burned area.
Kilovolt ampere (KVA).

14. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Stator windings.
12 to 15 times a minute.
Two speeds

15. 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...
Derive a neutral for grounding purposes.
Potential transformer.
Draw less current.
600 volts.

16. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
The motor rotation is reversed.
At the source transformer.
75 turns.

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.
At the source transformer.
Electro-magnetism for their operation.
5:1.
600 volts.

18. Operating coils - motors - transformers - relays and solenoids depend upon...
H terminals.
No.6 AWG.
Electro-magnetism for their operation.
Cut around clothing that has adhered to the burned area.

19. 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?
100 turns.
7 -630 volts.
5:1.
25 feet.

20. If any two-phase wires are reversed on a three-phase motor - the motor will...
H terminals.
25 feet.
Reverse its rotation.
Zero amps.

21. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
The capacitors should be discharged.
Zero amps.
They must be installed at least 7 feet above the ground.

22. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Electro-magnetism for their operation.
Isolation transformer.
480 volts.
100 turns.

23. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
No.6 AWG.
Transformer
A.C.

24. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Alternating current.
Two speeds
At the source transformer.
The capacitors should be discharged.

25. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Check to make sure that the victim is not still in contact with the electricity.
A grounding resistor.
A step-up transformer.
Kilovolt ampere (KVA).

26. The speed of an alternating current - squirrel-cage induction motor is...
25 feet.
Nearly constant.
Grounded phase and ground fault devices were not operating.
Kilovolt ampere (KVA).

27. 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...
The chest should rise or inflate.
5:1
100 volts.
Potential transformer.

28. What type of 3-phase AC motor is used most often around a mine?
60 Hertz
Squirrel-cage induction motor.
Transformer
They must be installed at least 7 feet above the ground.

29. The secondary windings on a 10:1 step-down transformer will have a wire size...
Because less current flowing at high voltage causes less line loss per kilowatt.
Capacitance.
The current will read zero.
Larger than that found in the primary winding.

30. The standard frequency of power supplied by the power company is...
Transformer
60 cycles per second (60 Hertz).
They should be made by the same manufacturer.
150 turns.

31. The primary function of a power transformer is to provide...
The sum of the two capacitors.
Full-load - three-phase voltage.
Circuit Breaker.
Provides single-phase power to smaller loads such as lights - heaters - etc.

32. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
150 turns.
Two speeds
A step-up transformer.
3 -979 Volts.

33. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
An electrical shock hazard may exist.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
60 cycles per second (60 Hertz).
Disconnect the frame-grounding conductor.

34. 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.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
60 Hertz
800 volts.

35. The primary leads of a single-phase transformer should be connected to the...
An electromagnet.
5:1.
The current will read zero.
H terminals.

36. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Transformers.
Inductance.
No.6 AWG.
The sum of the two capacitors.

37. Current that changes periodically in direction is...
Alternating current.
277 volts.
Squirrel-cage rotor.
Reverse any two-phase leads.

38. 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?
The motor rotation is reversed.
100 volts.
Squirrel-cage induction motor.
200 volts AC.

39. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Current changing constantly in magnitude and periodically in direction.
Disconnect the frame-grounding conductor.
800 volts.
277 volts.

40. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Draw less current.
Clamp-on ammeter.
Shunted and taped

41. The size of a transformer is measured in...
Draw less current.
H terminals.
Kilovolt ampere (KVA).
At least two phases

42. Not a symptom of electrical shock?.
25 feet.
Isolation transformer.
Hyperventilation.
75 turns.

43. 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.
They should be made by the same manufacturer.
Reverse any two-phase leads.
Check to make sure that the victim is not still in contact with the electricity.

44. Compared to the secondary of a loaded - step-down transformer - the primary has...
Because less current flowing at high voltage causes less line loss per kilowatt.
Lower current and higher voltage.
Four times less than that of the secondary.
The chest should rise or inflate.

45. What should the duty rating of a grounding resistor be?
7 -630 volts.
Squirrel-cage rotor.
Continuous.
Two speeds

46. Three-phase AC underground cables must be provided with overcurrent protection using a...
Cut around clothing that has adhered to the burned area.
Hyperventilation.
Circuit Breaker.
75 turns.

47. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Draw less current.
Four times less than that of the secondary.
5:1.
No.6 AWG.

48. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
They should be made by the same manufacturer.
The current will read zero.
Draw less current.

49. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Allow for metering voltage and Current.
Nearly constant.
Grounded phase and ground fault devices were not operating.

50. What type motor is a wound-rotor induction motor?
They should be made by the same manufacturer.
A.C.
2000 watts
Zero amps.