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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 transformer used only to measure voltage is a...
Potential transformer.
Transformers.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
An electromagnet.

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...
Tied together
Two speeds
Because less current flowing at high voltage causes less line loss per kilowatt.
60 cycles per second (60 Hertz).

3. Current that changes periodically in direction is...
Current changing constantly in magnitude and periodically in direction.
Alternating current.
A.C.
5:1.

4. A burn causing a blister is classified as a...
Inductance.
800 volts.
Second-degree burn.
Kilovolt ampere (KVA).

5. A transformer with a 1:1 ratio is usually a (an)...
Shunted and taped
Reverse any two-phase leads.
Second-degree burn.
Isolation transformer.

6. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Current changing constantly in magnitude and periodically in direction.
3 -979 Volts.
5:1.
Two speeds

7. The primary leads of a single-phase transformer should be connected to the...
Circuit Breaker.
Continuous.
H terminals.
Check to make sure that the victim is not still in contact with the electricity.

8. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Because less current flowing at high voltage causes less line loss per kilowatt.
The current will read zero.
The sum of the two capacitors.
75 turns.

9. At what rate should mouth-to-mouth resuscitation be applied?
800 volts.
12 to 15 times a minute.
Grounded phase and ground fault devices were not operating.
X.

10. Where should grounding resistors be located?
Reverse any two-phase leads.
A step-up transformer.
At the source transformer.
800 volts.

11. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Electro-magnetism for their operation.
277 volts.
Tied together
X.

12. The property of an electric circuit that opposes any change in current is called...
Derive a neutral for grounding purposes.
They must be installed at least 7 feet above the ground.
Inductance.
No.6 AWG.

13. The main function of CT's and PT's on a main substation is to...
200 volts AC.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Allow for metering voltage and Current.
Two speeds

14. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Circuit Breaker.
3 -979 Volts.
480 volts.
1 amp.

15. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Electro-magnetism for their operation.
7 -630 volts.
15 feet off the ground.
Inductance.

16. Not a symptom of electrical shock?.
Hyperventilation.
Kilovolt ampere (KVA).
An electromagnet.
Provides single-phase power to smaller loads such as lights - heaters - etc.

17. What type motor is a wound-rotor induction motor?
Transformers.
A.C.
Draw less current.
60 cycles per second (60 Hertz).

18. 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?
Tied together
Draw less current.
5:1.
150 turns.

19. The combined capacitance of two capacitors in parallel is...
Circuit Breaker.
Grounded phase and ground fault devices were not operating.
The sum of the two capacitors.
Current that changes constantly in magnitude and periodically in direction.

20. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
They should be made by the same manufacturer.
7 -630 volts.
Potential transformer.

21. What is the first step to be followed in aiding a victim of electrical shock?
200 volts AC.
Carotid pulse - which is located in the neck next to the Adam's apple.
100 volts.
Check to make sure that the victim is not still in contact with the electricity.

22. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Transformer
No.6 AWG.
A grounding resistor.
The current will read zero.

23. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
An electrical shock hazard may exist.
Disconnect the frame-grounding conductor.
They must be installed at least 7 feet above the ground.
At the source transformer.

24. The standard frequency of power supplied by the power company is...
150 turns.
Stator windings.
Derive a neutral for grounding purposes.
60 cycles per second (60 Hertz).

25. How do you change the direction of a 3-phase AC motor?
Lower current and higher voltage.
Reverse any two-phase leads.
Potential transformer.
100 turns.

26. When not connected to a load - the secondary leads of a current transformer should be...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Kilovolt ampere (KVA).
Reverse any two-phase leads.
Shunted and taped

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

28. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
2000 watts
They must be installed at least 7 feet above the ground.
480 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.

29. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
75 turns.
Grounded phase and ground fault devices were not operating.
An electrical shock hazard may exist.
7 -630 volts.

30. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Four times less than that of the secondary.
Capacitance.
7 -630 volts.
Grounded phase and ground fault devices were not operating.

31. A wound-rotor induction motor has all the following EXCEPT...
Four times less than that of the secondary.
Reverse its rotation.
Continuous.
Squirrel-cage rotor.

32. 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.
Current that changes constantly in magnitude and periodically in direction.
A step-up transformer.
Grounded phase and ground fault devices were not operating.

33. 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?
A step-up transformer.
Alternating current.
Tied together
800 volts.

34. Alternating current may be defined as...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Current that changes constantly in magnitude and periodically in direction.
5:1
800 volts.

35. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Hyperventilation.
Zero amps.
Reverse its rotation.

36. The purpose of a zig-zag transformer is to...
Reverse its rotation.
H terminals.
Squirrel-cage rotor.
Derive a neutral for grounding purposes.

37. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Grounded phase and ground fault devices were not operating.
Inductance.
A device used to store electrical energy.

38. The standard frequency of alternating current used at a mine is...
Short-circuited after power has been removed.
60 Hertz
They must be installed at least 7 feet above the ground.
Carotid pulse - which is located in the neck next to the Adam's apple.

39. 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
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Reverse its rotation.
Isolation transformer.

40. If any two-phase wires are reversed on a three-phase motor - the motor will...
The current will read zero.
Reverse its rotation.
Carotid pulse - which is located in the neck next to the Adam's apple.
800 volts.

41. How should clothing be removed from a burn?
Transformer
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.
Nearly constant.

42. AC voltage is raised or lowered by means of...
7 -630 volts.
Transformers.
An electromagnet.
Stator windings.

43. A solenoid coil is...
3 -979 Volts.
Stator windings.
An electromagnet.
75 turns.

44. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Second-degree burn.
No.6 AWG.
Transformer
They must be installed at least 7 feet above the ground.

45. What type of 3-phase AC motor is used most often around a mine?
Inductance.
Squirrel-cage induction motor.
200 volts AC.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

46. 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.
They should be made by the same manufacturer.
Kilovolt ampere (KVA).
5:1.

47. What is the danger when working around capacitors?
The chest should rise or inflate.
An electrical shock hazard may exist.
H terminals.
A grounding resistor.

48. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
The sum of the two capacitors.
25 feet.
It provides good speed control.
At least two phases

49. 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?
Cut around clothing that has adhered to the burned area.
Squirrel-cage induction motor.
3 -979 Volts.
Grounded phase and ground fault devices were not operating.

50. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
7 -630 volts.
Draw less current.
277 volts.