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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. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
A step-up transformer.
Squirrel-cage induction motor.
Tied together

2. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
12 to 15 times a minute.
Capacitance.
Second-degree burn.

3. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
5:1.
A grounding resistor.
15 feet off the ground.
Disconnect the frame-grounding conductor.

4. A control power transformer...
100 volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Because less current flowing at high voltage causes less line loss per kilowatt.
Shunted and taped

5. Find the turns ratio of a single-phase transformer with the following values: Primary power of 5KW - secondary current of 100 amps - and primary voltage of 250 volts.
5:1
Current changing constantly in magnitude and periodically in direction.
200 volts AC.
Two speeds

6. High voltage is used to transmit power over long distances...
A.C.
Electro-magnetism for their operation.
Because less current flowing at high voltage causes less line loss per kilowatt.
5:1

7. 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?
H terminals.
75 turns.
Lower current and higher voltage.
X.

8. What is the danger when working around capacitors?
An electrical shock hazard may exist.
Inductance.
15 feet off the ground.
At least two phases

9. 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?
800 volts.
Stator windings.
Inductance.
60 cycles per second (60 Hertz).

10. 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?
Inductance.
They must be installed at least 7 feet above the ground.
150 turns.
Reverse any two-phase leads.

11. The property of an electric circuit that opposes any change in current is called...
Reverse its rotation.
Inductance.
Current that changes constantly in magnitude and periodically in direction.
Four times less than that of the secondary.

12. The size of a transformer is measured in...
An electrical shock hazard may exist.
Lower current and higher voltage
Transformer
Kilovolt ampere (KVA).

13. Not true about AC power?
Grounded phase and ground fault devices were not operating.
It provides good speed control.
100 turns.
Larger than that found in the primary winding.

14. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Four times less than that of the secondary.
Current that changes constantly in magnitude and periodically in direction.
5:1
X.

15. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
100 turns.
Grounded phase and ground fault devices were not operating.
Two speeds
Squirrel-cage rotor.

16. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Allow for metering voltage and Current.
Capacitance.
The sum of the two capacitors.

17. 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...
Tied together
15 feet off the ground.
100 volts.
150 turns.

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

19. How should clothing be removed from a burn?
Check to make sure that the victim is not still in contact with the electricity.
Alternating current.
Cut around clothing that has adhered to the burned area.
Squirrel-cage rotor.

20. The transformer used only to measure voltage is a...
Potential transformer.
Tied together
An electrical shock hazard may exist.
Two speeds

21. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Check to make sure that the victim is not still in contact with the electricity.
The current will read zero.
The capacitors should be discharged.
150 turns.

22. The primary function of a power transformer is to provide...
An electromagnet.
2000 watts
Full-load - three-phase voltage.
Potential transformer.

23. The primary leads of a single-phase transformer should be connected to the...
Transformers.
A.C.
A device used to store electrical energy.
H terminals.

24. The secondary windings on a 10:1 step-down transformer will have a wire size...
An electromagnet.
Full-load - three-phase voltage.
Larger than that found in the primary winding.
Kilovolt ampere (KVA).

25. Define alternating current...
An electromagnet.
Current changing constantly in magnitude and periodically in direction.
Circuit Breaker.
60 Hertz

26. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
5:1.
A device used to store electrical energy.
Transformers.

27. Which of the following does a squirrel cage induction motor have?
600 volts.
Draw less current.
75 turns.
Stator windings.

28. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
A step-up transformer.
Inductance.
The motor rotation is reversed.
25 feet.

29. 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
Stator windings.
15 feet off the ground.
The chest should rise or inflate.

30. 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?
Short-circuited after power has been removed.
Allow for metering voltage and Current.
Nearly constant.
100 turns.

31. What should the duty rating of a grounding resistor be?
Circuit Breaker.
Grounded phase and ground fault devices were not operating.
Continuous.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

32. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
Reverse its rotation.
Squirrel-cage induction motor.
The sum of the two capacitors.

33. 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...
H terminals.
Reverse its rotation.
Tied together
The sum of the two capacitors.

34. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
The motor rotation is reversed.
Draw less current.
Zero amps.
3 -979 Volts.

35. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Check to make sure that the victim is not still in contact with the electricity.
Kilovolt ampere (KVA).
The motor rotation is reversed.
277 volts.

36. The standard frequency of alternating current used at a mine is...
Electro-magnetism for their operation.
Provides single-phase power to smaller loads such as lights - heaters - etc.
60 Hertz
200 volts AC.

37. Compared to the secondary of a loaded - step-down transformer - the primary has...
600 volts.
Short-circuited after power has been removed.
Lower current and higher voltage.
75 turns.

38. Alternating current may be defined as...
15 feet off the ground.
Transformers.
Allow for metering voltage and Current.
Current that changes constantly in magnitude and periodically in direction.

39. What is the first step to be followed in aiding a victim of electrical shock?
Shunted and taped
A device used to store electrical energy.
100 volts.
Check to make sure that the victim is not still in contact with the electricity.

40. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Lower current and higher voltage.
The current will read zero.
The motor rotation is reversed.
Zero amps.

41. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
100 volts.
Short-circuited after power has been removed.
Lower current and higher voltage
60 Hertz

42. 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.
Inductance.
No.6 AWG.
Draw less current.

43. What type of 3-phase AC motor is used most often around a mine?
Derive a neutral for grounding purposes.
Squirrel-cage induction motor.
Inductance.
7 -630 volts.

44. The main function of CT's and PT's on a main substation is to...
75 turns.
Lower current and higher voltage.
7 -630 volts.
Allow for metering voltage and Current.

45. To protect against over-current in a three-phase circuit over-current protection must be provided for...
277 volts.
Inductance.
At least two phases
75 turns.

46. All transformers step voltage up or down by...
480 volts.
Capacitance.
Inductance.
60 cycles per second (60 Hertz).

47. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Allow for metering voltage and Current.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
2000 watts
Carotid pulse - which is located in the neck next to the Adam's apple.

48. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
A.C.
480 volts.
2000 watts
An electromagnet.

49. The combined capacitance of two capacitors in parallel is...
Zero amps.
H terminals.
At the source transformer.
The sum of the two capacitors.

50. A burn causing a blister is classified as a...
Reverse its rotation.
Second-degree burn.
An electrical shock hazard may exist.
At least two phases