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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. 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.
Larger than that found in the primary winding.
Electro-magnetism for their operation.
Provides single-phase power to smaller loads such as lights - heaters - etc.

2. The property of an electric circuit that opposes any change in current is called...
Inductance.
Isolation transformer.
Circuit Breaker.
Check to make sure that the victim is not still in contact with the electricity.

3. Which of the following does a squirrel cage induction motor have?
Stator windings.
Grounded phase and ground fault devices were not operating.
12 to 15 times a minute.
At least two phases

4. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
3 -979 Volts.
Potential transformer.
A grounding resistor.

5. 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?
Inductance.
75 turns.
Shunted and taped
Cut around clothing that has adhered to the burned area.

6. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
H terminals.
150 turns.
100 volts.
They should be made by the same manufacturer.

7. What should the duty rating of a grounding resistor be?
Continuous.
Reverse its rotation.
An electromagnet.
Alternating current.

8. The size of a transformer is measured in...
480 volts.
Kilovolt ampere (KVA).
An electrical shock hazard may exist.
No.6 AWG.

9. The standard frequency of alternating current used at a mine is...
60 Hertz
Squirrel-cage induction motor.
75 turns.
5:1.

10. 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.
Grounded phase and ground fault devices were not operating.
X.

11. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
A step-up transformer.
Lower current and higher voltage
The current will read zero.
H terminals.

12. The transformer used only to measure voltage is a...
Potential transformer.
Draw less current.
60 Hertz
5:1.

13. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
15 feet off the ground.
Hyperventilation.
60 Hertz

14. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Four times less than that of the secondary.
3 -979 Volts.
It provides good speed control.
Two speeds

15. How should clothing be removed from a burn?
100 turns.
Cut around clothing that has adhered to the burned area.
A step-up transformer.
Kilovolt ampere (KVA).

16. A burn causing a blister is classified as a...
Second-degree burn.
600 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
75 turns.

17. Current transformers - or CT's - are used to...
Second-degree burn.
Alternating current.
Carotid pulse - which is located in the neck next to the Adam's apple.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

18. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Tied together
3 -979 Volts.
No.6 AWG.
The chest should rise or inflate.

19. A solenoid coil is...
An electromagnet.
Circuit Breaker.
Tied together
Hyperventilation.

20. The property of an electrical circuit that opposes any change in voltage is called...
They should be made by the same manufacturer.
5:1
Capacitance.
X.

21. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
No.6 AWG.
2000 watts
A step-up transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.

22. The main function of CT's and PT's on a main substation is to...
Circuit Breaker.
Zero amps.
X.
Allow for metering voltage and Current.

23. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
3 -979 Volts.
Larger than that found in the primary winding.
Alternating current.
480 volts.

24. The primary leads of a single-phase transformer should be connected to the...
Check to make sure that the victim is not still in contact with the electricity.
The capacitors should be discharged.
H terminals.
150 turns.

25. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
A grounding resistor.
2000 watts
Isolation transformer.

26. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Reverse its rotation.
Two speeds
Larger than that found in the primary winding.
X.

27. 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.
Isolation transformer.
Shunted and taped
5:1.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

28. Define alternating current...
Inductance.
Current changing constantly in magnitude and periodically in direction.
12 to 15 times a minute.
480 volts.

29. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Inductance.
480 volts.
At the source transformer.
Grounded phase and ground fault devices were not operating.

30. All transformers step voltage up or down by...
3 -979 Volts.
Inductance.
An electrical shock hazard may exist.
Zero amps.

31. Not true about AC power?
It provides good speed control.
5:1
277 volts.
Disconnect the frame-grounding conductor.

32. Alternating current may be defined as...
Grounded phase and ground fault devices were not operating.
60 Hertz
Current that changes constantly in magnitude and periodically in direction.
480 volts.

33. The secondary windings on a 10:1 step-down transformer will have a wire size...
The motor rotation is reversed.
Inductance.
Squirrel-cage induction motor.
Larger than that found in the primary winding.

34. Current in an AC circuit may be measured by...
Squirrel-cage induction motor.
Clamp-on ammeter.
At the source transformer.
12 to 15 times a minute.

35. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Cut around clothing that has adhered to the burned area.
At least two phases
Lower current and higher voltage
At the source transformer.

36. The primary function of a power transformer is to provide...
5:1
Inductance.
Full-load - three-phase voltage.
The motor rotation is reversed.

37. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
Isolation transformer.
Tied together
5:1.

38. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Second-degree burn.
A grounding resistor.
Capacitance.

39. 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?
Tied together
100 turns.
The current will read zero.
12 to 15 times a minute.

40. 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.
The motor rotation is reversed.
Carotid pulse - which is located in the neck next to the Adam's apple.
Provides single-phase power to smaller loads such as lights - heaters - etc.

41. 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?
Zero amps.
A step-up transformer.
75 turns.
A.C.

42. Where should grounding resistors be located?
Capacitance.
60 cycles per second (60 Hertz).
At the source transformer.
Kilovolt ampere (KVA).

43. Not a symptom of electrical shock?.
12 to 15 times a minute.
A grounding resistor.
Hyperventilation.
277 volts.

44. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Derive a neutral for grounding purposes.
1 amp.
800 volts.
2000 watts

45. What type motor is a wound-rotor induction motor?
12 to 15 times a minute.
Draw less current.
A device used to store electrical energy.
A.C.

46. A transformer with a 1:1 ratio is usually a (an)...
Because less current flowing at high voltage causes less line loss per kilowatt.
Isolation transformer.
75 turns.
2000 watts

47. 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
A grounding resistor.
3 -979 Volts.
600 volts.

48. A wound-rotor induction motor has all the following EXCEPT...
Stator windings.
100 turns.
800 volts.
Squirrel-cage rotor.

49. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
A.C.
Current that changes constantly in magnitude and periodically in direction.
Four times less than that of the secondary.
The sum of the two capacitors.

50. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
480 volts.
60 cycles per second (60 Hertz).
Carotid pulse - which is located in the neck next to the Adam's apple.