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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 danger when working around capacitors?
An electrical shock hazard may exist.
Stator windings.
Nearly constant.
Alternating current.

2. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
At least two phases
Reverse its rotation.
The motor rotation is reversed.

3. 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.
Current that changes constantly in magnitude and periodically in direction.
800 volts.
75 turns.

4. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
150 turns.
2000 watts
Disconnect the frame-grounding conductor.
Draw less current.

5. Which of the following does a squirrel cage induction motor have?
Hyperventilation.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Stator windings.
Tied together

6. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
15 feet off the ground.
Continuous.
The chest should rise or inflate.
Grounded phase and ground fault devices were not operating.

7. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Because less current flowing at high voltage causes less line loss per kilowatt.
Draw less current.
7 -630 volts.
Zero amps.

8. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
H terminals.
Four times less than that of the secondary.
A grounding resistor.
Squirrel-cage rotor.

9. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Draw less current.
Squirrel-cage rotor.
60 Hertz
15 feet off the ground.

10. 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.
A step-up transformer.
A device used to store electrical energy.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

11. 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?
Transformer
The chest should rise or inflate.
100 turns.
Kilovolt ampere (KVA).

12. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
A grounding resistor.
They must be installed at least 7 feet above the ground.
Hyperventilation.
No.6 AWG.

13. 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?
Lower current and higher voltage
The sum of the two capacitors.
They should be made by the same manufacturer.
600 volts.

14. Three-phase AC underground cables must be provided with overcurrent protection using a...
Potential transformer.
Circuit Breaker.
H terminals.
Stator windings.

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

16. What should the duty rating of a grounding resistor be?
7 -630 volts.
Continuous.
Hyperventilation.
12 to 15 times a minute.

17. 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?
A step-up transformer.
75 turns.
5:1.
Stator windings.

18. The size of a transformer is measured in...
1 amp.
Alternating current.
Carotid pulse - which is located in the neck next to the Adam's apple.
Kilovolt ampere (KVA).

19. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Reverse any two-phase leads.
The motor rotation is reversed.
It provides good speed control.
Inductance.

20. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
Circuit Breaker.
Cut around clothing that has adhered to the burned area.
Disconnect the frame-grounding conductor.

21. The primary leads of a single-phase transformer should be connected to the...
Lower current and higher voltage
Grounded phase and ground fault devices were not operating.
H terminals.
200 volts AC.

22. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Second-degree burn.
Two speeds
Clamp-on ammeter.
480 volts.

23. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
Continuous.
800 volts.
An electromagnet.

24. What steps up or steps down AC voltage?
Transformer
It provides good speed control.
Lower current and higher voltage
5:1.

25. 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.
Tied together
An electromagnet.
100 turns.

26. 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?
3 -979 Volts.
Squirrel-cage induction motor.
150 turns.
15 feet off the ground.

27. 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.
1 amp.
Reverse its rotation.
Hyperventilation.

28. Alternating current may be defined as...
Shunted and taped
5:1.
Current that changes constantly in magnitude and periodically in direction.
25 feet.

29. Not true about AC power?
It provides good speed control.
200 volts AC.
Disconnect the frame-grounding conductor.
Alternating current.

30. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Allow for metering voltage and Current.
Short-circuited after power has been removed.
The sum of the two capacitors.
Derive a neutral for grounding purposes.

31. If any two-phase wires are reversed on a three-phase motor - the motor will...
Current that changes constantly in magnitude and periodically in direction.
Reverse its rotation.
200 volts AC.
Grounded phase and ground fault devices were not operating.

32. The combined capacitance of two capacitors in parallel is...
Stator windings.
600 volts.
The sum of the two capacitors.
Four times less than that of the secondary.

33. What is the first step to be followed in aiding a victim of electrical shock?
H terminals.
Larger than that found in the primary winding.
Carotid pulse - which is located in the neck next to the Adam's apple.
Check to make sure that the victim is not still in contact with the electricity.

34. Compared to the secondary of a loaded - step-down transformer - the primary has...
Tied together
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Lower current and higher voltage
Capacitance.

35. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
Current changing constantly in magnitude and periodically in direction.
An electrical shock hazard may exist.
Provides single-phase power to smaller loads such as lights - heaters - etc.

36. 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?
3 -979 Volts.
Hyperventilation.
The current will read zero.
800 volts.

37. Current that changes periodically in direction is...
X.
Two speeds
12 to 15 times a minute.
Alternating current.

38. Two 10-hp induction motors are operating on 460 volts AC. One motor is connected by single- phase; the other is connected in three-phase. The three-phase will...
Transformer
Draw less current.
Continuous.
Derive a neutral for grounding purposes.

39. The property of an electrical circuit that opposes any change in voltage is called...
An electromagnet.
A grounding resistor.
Capacitance.
Cut around clothing that has adhered to the burned area.

40. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
3 -979 Volts.
The motor rotation is reversed.
1 amp.
Transformer

41. 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
60 cycles per second (60 Hertz).
Reverse its rotation.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

42. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
12 to 15 times a minute.
Potential transformer.
At the source transformer.
25 feet.

43. A transformer with a 1:1 ratio is usually a (an)...
Reverse its rotation.
Isolation transformer.
Inductance.
The sum of the two capacitors.

44. High voltage is used to transmit power over long distances...
Alternating current.
Because less current flowing at high voltage causes less line loss per kilowatt.
Larger than that found in the primary winding.
A device used to store electrical energy.

45. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Larger than that found in the primary winding.
A step-up transformer.
2000 watts
277 volts.

46. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Electro-magnetism for their operation.
Inductance.
480 volts.
Zero amps.

47. To protect against over-current in a three-phase circuit over-current protection must be provided for...
12 to 15 times a minute.
The sum of the two capacitors.
Current that changes constantly in magnitude and periodically in direction.
At least two phases

48. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Provides single-phase power to smaller loads such as lights - heaters - etc.
The chest should rise or inflate.
480 volts.
800 volts.

49. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
800 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Circuit Breaker.
Transformers.

50. Compared to the secondary of a loaded - step-down transformer - the primary has...
It provides good speed control.
Lower current and higher voltage.
60 Hertz
The current will read zero.