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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. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Full-load - three-phase voltage.
The capacitors should be discharged.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Squirrel-cage induction motor.

2. What steps up or steps down AC voltage?
The sum of the two capacitors.
15 feet off the ground.
Transformers.
Transformer

3. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
100 volts.
Grounded phase and ground fault devices were not operating.
25 feet.
Carotid pulse - which is located in the neck next to the Adam's apple.

4. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
12 to 15 times a minute.
800 volts.
480 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.

5. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Grounded phase and ground fault devices were not operating.
Clamp-on ammeter.
277 volts.
The capacitors should be discharged.

6. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
200 volts AC.
Capacitance.
Squirrel-cage rotor.
The capacitors should be discharged.

7. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Disconnect the frame-grounding conductor.
Larger than that found in the primary winding.
Zero amps.
Reverse any two-phase leads.

8. How do you change the direction of a 3-phase AC motor?
Capacitance.
Reverse any two-phase leads.
Alternating current.
Squirrel-cage rotor.

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?
100 turns.
Capacitance.
800 volts.
12 to 15 times a minute.

10. Current that changes periodically in direction is...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Alternating current.
Continuous.
The motor rotation is reversed.

11. Where should grounding resistors be located?
At the source transformer.
Two speeds
600 volts.
5:1.

12. When not connected to a load - the secondary leads of a current transformer should be...
Zero amps.
Check to make sure that the victim is not still in contact with the electricity.
Larger than that found in the primary winding.
Shunted and taped

13. Alternating current may be defined as...
800 volts.
5:1
Current that changes constantly in magnitude and periodically in direction.
Electro-magnetism for their operation.

14. The speed of an alternating current - squirrel-cage induction motor is...
Current that changes constantly in magnitude and periodically in direction.
Clamp-on ammeter.
Electro-magnetism for their operation.
Nearly constant.

15. Not true about AC power?
A step-up transformer.
The current will read zero.
It provides good speed control.
Draw less current.

16. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
150 turns.
Disconnect the frame-grounding conductor.
Derive a neutral for grounding purposes.
Allow for metering voltage and Current.

17. 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...
Inductance.
X.
Tied together
Transformers.

18. The combined capacitance of two capacitors in parallel is...
Provides single-phase power to smaller loads such as lights - heaters - etc.
They must be installed at least 7 feet above the ground.
The sum of the two capacitors.
75 turns.

19. Current transformers - or CT's - are used to...
15 feet off the ground.
They should be made by the same manufacturer.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The sum of the two capacitors.

20. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Derive a neutral for grounding purposes.
Two speeds
1 amp.
Carotid pulse - which is located in the neck next to the Adam's apple.

21. Which of the following does a squirrel cage induction motor have?
Reverse any two-phase leads.
No.6 AWG.
H terminals.
Stator windings.

22. The primary leads of a single-phase transformer should be connected to the...
12 to 15 times a minute.
25 feet.
They must be installed at least 7 feet above the ground.
H terminals.

23. 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?
75 turns.
Current that changes constantly in magnitude and periodically in direction.
Squirrel-cage rotor.
60 cycles per second (60 Hertz).

24. A transformer with a 1:1 ratio is usually a (an)...
No.6 AWG.
Isolation transformer.
Inductance.
Reverse any two-phase leads.

25. 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.
Hyperventilation.
No.6 AWG.
At the source transformer.

26. Compared to the secondary of a loaded - step-down transformer - the primary has...
Allow for metering voltage and Current.
Lower current and higher voltage
Provides single-phase power to smaller loads such as lights - heaters - etc.
Squirrel-cage induction motor.

27. How should clothing be removed from a burn?
Inductance.
Grounded phase and ground fault devices were not operating.
A device used to store electrical energy.
Cut around clothing that has adhered to the burned area.

28. The transformer used only to measure voltage is a...
Potential transformer.
Reverse its rotation.
Squirrel-cage rotor.
75 turns.

29. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
It provides good speed control.
Shunted and taped
The capacitors should be discharged.

30. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Check to make sure that the victim is not still in contact with the electricity.
Kilovolt ampere (KVA).
The capacitors should be discharged.
Short-circuited after power has been removed.

31. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Transformers.
Squirrel-cage rotor.
A grounding resistor.
Continuous.

32. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
Full-load - three-phase voltage.
277 volts.
Capacitance.

33. The secondary windings on a 10:1 step-down transformer will have a wire size...
Allow for metering voltage and Current.
Squirrel-cage induction motor.
Larger than that found in the primary winding.
An electromagnet.

34. 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.
15 feet off the ground.
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.

35. A wound-rotor induction motor has all the following EXCEPT...
The motor rotation is reversed.
5:1
Squirrel-cage rotor.
5:1.

36. The size of a transformer is measured in...
The capacitors should be discharged.
Reverse any two-phase leads.
Zero amps.
Kilovolt ampere (KVA).

37. What is a capacitor?
The motor rotation is reversed.
3 -979 Volts.
A device used to store electrical energy.
12 to 15 times a minute.

38. A burn causing a blister is classified as a...
It provides good speed control.
Draw less current.
Second-degree burn.
Squirrel-cage rotor.

39. The standard frequency of power supplied by the power company is...
Transformers.
The sum of the two capacitors.
The current will read zero.
60 cycles per second (60 Hertz).

40. A control power transformer...
Circuit Breaker.
277 volts.
Four times less than that of the secondary.
Provides single-phase power to smaller loads such as lights - heaters - etc.

41. AC voltage is raised or lowered by means of...
1 amp.
Transformers.
200 volts AC.
5:1

42. A solenoid coil is...
The motor rotation is reversed.
Reverse its rotation.
An electromagnet.
12 to 15 times a minute.

43. All transformers step voltage up or down by...
5:1.
Shunted and taped
277 volts.
Inductance.

44. At what rate should mouth-to-mouth resuscitation be applied?
Current changing constantly in magnitude and periodically in direction.
12 to 15 times a minute.
Inductance.
Full-load - three-phase voltage.

45. What should the duty rating of a grounding resistor be?
Alternating current.
Continuous.
Clamp-on ammeter.
25 feet.

46. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Electro-magnetism for their operation.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Reverse any two-phase leads.

47. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
A grounding resistor.
75 turns.
The chest should rise or inflate.
Cut around clothing that has adhered to the burned area.

48. The main function of CT's and PT's on a main substation is to...
H terminals.
277 volts.
Allow for metering voltage and Current.
Larger than that found in the primary winding.

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?
200 volts AC.
The motor rotation is reversed.
600 volts.
3 -979 Volts.

50. 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...
It provides good speed control.
Second-degree burn.
5:1.
Draw less current.