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Test your basic knowledge |

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 wound-rotor induction motor has all the following EXCEPT...
480 volts.
The current will read zero.
Transformer
Squirrel-cage rotor.

2. 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...
Draw less current.
7 -630 volts.
Tied together
Disconnect the frame-grounding conductor.

3. 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?
1 amp.
Nearly constant.
Because less current flowing at high voltage causes less line loss per kilowatt.
150 turns.

4. AC voltage is raised or lowered by means of...
Check to make sure that the victim is not still in contact with the electricity.
Transformers.
Derive a neutral for grounding purposes.
Transformer

5. Not a symptom of electrical shock?.
60 Hertz
Lower current and higher voltage.
Shunted and taped
Hyperventilation.

6. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Squirrel-cage induction motor.
Transformer
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Lower current and higher voltage.

7. At what rate should mouth-to-mouth resuscitation be applied?
The chest should rise or inflate.
A step-up transformer.
Full-load - three-phase voltage.
12 to 15 times a minute.

8. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Shunted and taped
Full-load - three-phase voltage.
7 -630 volts.
Two speeds

9. What type motor is a wound-rotor induction motor?
480 volts.
Reverse its rotation.
Carotid pulse - which is located in the neck next to the Adam's apple.
A.C.

10. Which of the following does a squirrel cage induction motor have?
Stator windings.
No.6 AWG.
12 to 15 times a minute.
Reverse any two-phase leads.

11. What should the duty rating of a grounding resistor be?
Continuous.
X.
Transformers.
2000 watts

12. 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.
25 feet.
Transformers.
5:1.
12 to 15 times a minute.

13. A burn causing a blister is classified as a...
They must be installed at least 7 feet above the ground.
3 -979 Volts.
Second-degree burn.
An electrical shock hazard may exist.

14. 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.
At the source transformer.
Lower current and higher voltage.
Potential transformer.

15. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
The current will read zero.
They must be installed at least 7 feet above the ground.
2000 watts
15 feet off the ground.

16. High voltage is used to transmit power over long distances...
75 turns.
Because less current flowing at high voltage causes less line loss per kilowatt.
Check to make sure that the victim is not still in contact with the electricity.
Allow for metering voltage and Current.

17. The size of a transformer is measured in...
Kilovolt ampere (KVA).
800 volts.
Draw less current.
25 feet.

18. The main function of CT's and PT's on a main substation is to...
Carotid pulse - which is located in the neck next to the Adam's apple.
The chest should rise or inflate.
75 turns.
Allow for metering voltage and Current.

19. 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...
Inductance.
Reverse any two-phase leads.
Check to make sure that the victim is not still in contact with the electricity.
100 volts.

20. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Isolation transformer.
5:1.
They should be made by the same manufacturer.
Lower current and higher voltage.

21. The purpose of a zig-zag transformer is to...
60 Hertz
25 feet.
Derive a neutral for grounding purposes.
The chest should rise or inflate.

22. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
600 volts.
The capacitors should be discharged.
An electromagnet.
Potential transformer.

23. The primary function of a power transformer is to provide...
5:1
Full-load - three-phase voltage.
277 volts.
Circuit Breaker.

24. 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
The chest should rise or inflate.
Draw less current.
Check to make sure that the victim is not still in contact with the electricity.

25. 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.
Potential transformer.
Four times less than that of the secondary.
75 turns.

26. Where should grounding resistors be located?
Circuit Breaker.
The chest should rise or inflate.
Lower current and higher voltage.
At the source transformer.

27. How should clothing be removed from a burn?
An electromagnet.
Cut around clothing that has adhered to the burned area.
Short-circuited after power has been removed.
150 turns.

28. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
Four times less than that of the secondary.
Grounded phase and ground fault devices were not operating.
277 volts.

29. 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...
Larger than that found in the primary winding.
Transformers.
Draw less current.
The chest should rise or inflate.

30. What is a capacitor?
At the source transformer.
A device used to store electrical energy.
Zero amps.
Larger than that found in the primary winding.

31. When not connected to a load - the secondary leads of a current transformer should be...
Full-load - three-phase voltage.
Shunted and taped
Kilovolt ampere (KVA).
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

32. 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?
Electro-magnetism for their operation.
A grounding resistor.
Nearly constant.
75 turns.

33. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
The current will read zero.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Cut around clothing that has adhered to the burned area.

34. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
480 volts.
150 turns.
At least two phases
Short-circuited after power has been removed.

35. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Kilovolt ampere (KVA).
The chest should rise or inflate.
Check to make sure that the victim is not still in contact with the electricity.
Cut around clothing that has adhered to the burned area.

36. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
Short-circuited after power has been removed.
5:1.
At least two phases

37. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
A grounding resistor.
An electromagnet.
Lower current and higher voltage

38. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
It provides good speed control.
Check to make sure that the victim is not still in contact with the electricity.
The sum of the two capacitors.
A grounding resistor.

39. Compared to the secondary of a loaded - step-down transformer - the primary has...
Kilovolt ampere (KVA).
Squirrel-cage rotor.
Lower current and higher voltage
No.6 AWG.

40. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
A device used to store electrical energy.
Disconnect the frame-grounding conductor.
600 volts.
Transformers.

41. What is the first step to be followed in aiding a victim of electrical shock?
Capacitance.
Check to make sure that the victim is not still in contact with the electricity.
25 feet.
Inductance.

42. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
60 cycles per second (60 Hertz).
12 to 15 times a minute.
Four times less than that of the secondary.
25 feet.

43. If any two-phase wires are reversed on a three-phase motor - the motor will...
Kilovolt ampere (KVA).
The current will read zero.
Reverse its rotation.
Lower current and higher voltage

44. The transformer used only to measure voltage is a...
100 turns.
Lower current and higher voltage
They must be installed at least 7 feet above the ground.
Potential transformer.

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

46. Current in an AC circuit may be measured by...
Lower current and higher voltage.
5:1.
Carotid pulse - which is located in the neck next to the Adam's apple.
Clamp-on ammeter.

47. The standard frequency of alternating current used at a mine is...
100 volts.
100 turns.
150 turns.
60 Hertz

48. What type of 3-phase AC motor is used most often around a mine?
Shunted and taped
75 turns.
60 Hertz
Squirrel-cage induction motor.

49. Current transformers - or CT's - are used to...
Kilovolt ampere (KVA).
A.C.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
A grounding resistor.

50. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The motor rotation is reversed.
The chest should rise or inflate.
A step-up transformer.
150 turns.