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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. At what rate should mouth-to-mouth resuscitation be applied?
Carotid pulse - which is located in the neck next to the Adam's apple.
12 to 15 times a minute.
800 volts.
100 volts.

2. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Lower current and higher voltage.
An electromagnet.
800 volts.
Zero amps.

3. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Zero amps.
480 volts.
60 cycles per second (60 Hertz).
5:1.

4. What is the danger when working around capacitors?
Grounded phase and ground fault devices were not operating.
An electrical shock hazard may exist.
25 feet.
Check to make sure that the victim is not still in contact with the electricity.

5. The property of an electric circuit that opposes any change in current is called...
Reverse its rotation.
Inductance.
3 -979 Volts.
Tied together

6. 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?
150 turns.
Current changing constantly in magnitude and periodically in direction.
Grounded phase and ground fault devices were not operating.
Reverse any two-phase leads.

7. A control power transformer...
75 turns.
Provides single-phase power to smaller loads such as lights - heaters - etc.
An electromagnet.
Reverse any two-phase leads.

8. AC voltage is raised or lowered by means of...
Transformers.
Draw less current.
Squirrel-cage rotor.
The current will read zero.

9. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The sum of the two capacitors.
The current will read zero.
Lower current and higher voltage.
Check to make sure that the victim is not still in contact with the electricity.

10. 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...
75 turns.
At least two phases
15 feet off the ground.
100 volts.

11. The combined capacitance of two capacitors in parallel is...
75 turns.
Cut around clothing that has adhered to the burned area.
The sum of the two capacitors.
Two speeds

12. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A grounding resistor.
Transformers.
Two speeds
X.

13. Where should grounding resistors be located?
3 -979 Volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
15 feet off the ground.
At the source transformer.

14. Current that changes periodically in direction is...
The capacitors should be discharged.
Alternating current.
Clamp-on ammeter.
At least two phases

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

16. Three-phase AC underground cables must be provided with overcurrent protection using a...
Allow for metering voltage and Current.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
A step-up transformer.
Circuit Breaker.

17. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
Stator windings.
Clamp-on ammeter.
Alternating current.

18. Compared to the secondary of a loaded - step-down transformer - the primary has...
Grounded phase and ground fault devices were not operating.
Lower current and higher voltage
Clamp-on ammeter.
15 feet off the ground.

19. 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
2000 watts
Transformer
100 volts.

20. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
1 amp.
Second-degree burn.
Grounded phase and ground fault devices were not operating.

21. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
Current that changes constantly in magnitude and periodically in direction.
At the source transformer.
Four times less than that of the secondary.

22. The size of a transformer is measured in...
Kilovolt ampere (KVA).
Lower current and higher voltage
Capacitance.
100 volts.

23. Which of the following does a squirrel cage induction motor have?
Disconnect the frame-grounding conductor.
Short-circuited after power has been removed.
Stator windings.
Potential transformer.

24. 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?
60 cycles per second (60 Hertz).
200 volts AC.
Isolation transformer.
An electrical shock hazard may exist.

25. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
Current changing constantly in magnitude and periodically in direction.
15 feet off the ground.
Circuit Breaker.

26. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
Kilovolt ampere (KVA).
Transformers.
Short-circuited after power has been removed.

27. To protect against over-current in a three-phase circuit over-current protection must be provided for...
60 cycles per second (60 Hertz).
At least two phases
The sum of the two capacitors.
Carotid pulse - which is located in the neck next to the Adam's apple.

28. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Two speeds
The current will read zero.
The chest should rise or inflate.
They should be made by the same manufacturer.

29. The standard frequency of alternating current used at a mine is...
150 turns.
Nearly constant.
Short-circuited after power has been removed.
60 Hertz

30. Not true about AC power?
It provides good speed control.
Lower current and higher voltage.
Isolation transformer.
800 volts.

31. What type motor is a wound-rotor induction motor?
A.C.
The motor rotation is reversed.
15 feet off the ground.
Check to make sure that the victim is not still in contact with the electricity.

32. 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.
The chest should rise or inflate.
The motor rotation is reversed.
Isolation transformer.

33. What steps up or steps down AC voltage?
Inductance.
Alternating current.
Electro-magnetism for their operation.
Transformer

34. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Cut around clothing that has adhered to the burned area.
600 volts.
The capacitors should be discharged.
Because less current flowing at high voltage causes less line loss per kilowatt.

35. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Two speeds
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
At least two phases
Circuit Breaker.

36. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Circuit Breaker.
Potential transformer.
100 volts.
The chest should rise or inflate.

37. What type of 3-phase AC motor is used most often around a mine?
Continuous.
Reverse its rotation.
Lower current and higher voltage
Squirrel-cage induction motor.

38. How do you change the direction of a 3-phase AC motor?
The chest should rise or inflate.
Full-load - three-phase voltage.
Reverse any two-phase leads.
Allow for metering voltage and Current.

39. 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...
Grounded phase and ground fault devices were not operating.
Tied together
Full-load - three-phase voltage.
Clamp-on ammeter.

40. 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
277 volts.
Draw less current.
7 -630 volts.

41. 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.
60 cycles per second (60 Hertz).
The capacitors should be discharged.
Current changing constantly in magnitude and periodically in direction.
5:1.

42. Current in an AC circuit may be measured by...
2000 watts
Clamp-on ammeter.
12 to 15 times a minute.
75 turns.

43. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Tied together
1 amp.
Transformers.
Shunted and taped

44. All transformers step voltage up or down by...
Second-degree burn.
Disconnect the frame-grounding conductor.
Cut around clothing that has adhered to the burned area.
Inductance.

45. What is a capacitor?
The capacitors should be discharged.
Disconnect the frame-grounding conductor.
A device used to store electrical energy.
25 feet.

46. 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.
A grounding resistor.
1 amp.
Squirrel-cage induction motor.

47. The transformer used only to measure voltage is a...
Squirrel-cage induction motor.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Potential transformer.
Lower current and higher voltage.

48. A solenoid coil is...
An electromagnet.
Circuit Breaker.
Transformer
H terminals.

49. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
X.
Grounded phase and ground fault devices were not operating.
3 -979 Volts.
Check to make sure that the victim is not still in contact with the electricity.

50. A burn causing a blister is classified as a...
A device used to store electrical energy.
Shunted and taped
Second-degree burn.
Lower current and higher voltage