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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 steps up or steps down AC voltage?
Transformer
Derive a neutral for grounding purposes.
X.
1 amp.

2. The standard frequency of alternating current used at a mine is...
60 Hertz
Short-circuited after power has been removed.
1 amp.
Disconnect the frame-grounding conductor.

3. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
800 volts.
A.C.
Zero amps.
The current will read zero.

4. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
H terminals.
600 volts.
A.C.
Four times less than that of the secondary.

5. A burn causing a blister is classified as a...
Transformers.
Second-degree burn.
The motor rotation is reversed.
Stator windings.

6. What should the duty rating of a grounding resistor be?
Cut around clothing that has adhered to the burned area.
Capacitance.
100 volts.
Continuous.

7. Where should grounding resistors be located?
The chest should rise or inflate.
It provides good speed control.
Current that changes constantly in magnitude and periodically in direction.
At the source transformer.

8. AC voltage is raised or lowered by means of...
75 turns.
A grounding resistor.
Lower current and higher voltage
Transformers.

9. The main function of CT's and PT's on a main substation is to...
The sum of the two capacitors.
Current changing constantly in magnitude and periodically in direction.
Allow for metering voltage and Current.
Squirrel-cage rotor.

10. The property of an electrical circuit that opposes any change in voltage is called...
Kilovolt ampere (KVA).
Capacitance.
2000 watts
Disconnect the frame-grounding conductor.

11. High voltage is used to transmit power over long distances...
An electrical shock hazard may exist.
Because less current flowing at high voltage causes less line loss per kilowatt.
Current changing constantly in magnitude and periodically in direction.
Squirrel-cage induction motor.

12. The property of an electric circuit that opposes any change in current is called...
Inductance.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
15 feet off the ground.
Draw less current.

13. The purpose of a zig-zag transformer is to...
12 to 15 times a minute.
Continuous.
Short-circuited after power has been removed.
Derive a neutral for grounding purposes.

14. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Short-circuited after power has been removed.
Squirrel-cage induction motor.
The capacitors should be discharged.
60 Hertz

15. What is the danger when working around capacitors?
X.
100 volts.
An electrical shock hazard may exist.
It provides good speed control.

16. The standard frequency of power supplied by the power company is...
The chest should rise or inflate.
60 cycles per second (60 Hertz).
Check to make sure that the victim is not still in contact with the electricity.
Hyperventilation.

17. 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...
Current that changes constantly in magnitude and periodically in direction.
They should be made by the same manufacturer.
5:1
Draw less current.

18. What type motor is a wound-rotor induction motor?
Zero amps.
75 turns.
Two speeds
A.C.

19. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
X.
12 to 15 times a minute.
277 volts.

20. The transformer used only to measure voltage is a...
Potential transformer.
Squirrel-cage rotor.
Disconnect the frame-grounding conductor.
600 volts.

21. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
15 feet off the ground.
Short-circuited after power has been removed.
Transformer
Carotid pulse - which is located in the neck next to the Adam's apple.

22. 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.
Continuous.
25 feet.
100 turns.

23. A control power transformer...
A.C.
Squirrel-cage rotor.
Provides single-phase power to smaller loads such as lights - heaters - etc.
H terminals.

24. If any two-phase wires are reversed on a three-phase motor - the motor will...
H terminals.
25 feet.
Reverse its rotation.
100 volts.

25. Not true about AC power?
Current changing constantly in magnitude and periodically in direction.
Shunted and taped
3 -979 Volts.
It provides good speed control.

26. Compared to the secondary of a loaded - step-down transformer - the primary has...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
5:1.
Carotid pulse - which is located in the neck next to the Adam's apple.
Lower current and higher voltage.

27. 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?
Second-degree burn.
100 turns.
Inductance.
An electrical shock hazard may exist.

28. Which of the following does a squirrel cage induction motor have?
H terminals.
Stator windings.
Four times less than that of the secondary.
Cut around clothing that has adhered to the burned area.

29. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
2000 watts
Reverse its rotation.
A grounding resistor.
Two speeds

30. 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.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
X.
Reverse any two-phase leads.

31. When not connected to a load - the secondary leads of a current transformer should be...
Electro-magnetism for their operation.
Shunted and taped
75 turns.
The chest should rise or inflate.

32. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
600 volts.
Electro-magnetism for their operation.
Clamp-on ammeter.

33. 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.
Nearly constant.
Because less current flowing at high voltage causes less line loss per kilowatt.
75 turns.

34. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
200 volts AC.
An electrical shock hazard may exist.
Continuous.

35. 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?
Allow for metering voltage and Current.
They must be installed at least 7 feet above the ground.
100 turns.
150 turns.

36. All transformers step voltage up or down by...
At least two phases
Inductance.
Short-circuited after power has been removed.
A grounding resistor.

37. What is a capacitor?
12 to 15 times a minute.
A device used to store electrical energy.
At the source transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.

38. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Reverse any two-phase leads.
Potential transformer.
12 to 15 times a minute.
2000 watts

39. 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?
Shunted and taped
100 turns.
Alternating current.
200 volts AC.

40. 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.
Current changing constantly in magnitude and periodically in direction.
5:1.
200 volts AC.
Draw less current.

41. 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...
Draw less current.
Derive a neutral for grounding purposes.
100 volts.
Second-degree burn.

42. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Inductance.
Circuit Breaker.
An electrical shock hazard may exist.
1 amp.

43. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Allow for metering voltage and Current.
An electromagnet.
Hyperventilation.

44. Alternating current may be defined as...
7 -630 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Lower current and higher voltage
Current that changes constantly in magnitude and periodically in direction.

45. The secondary windings on a 10:1 step-down transformer will have a wire size...
Current changing constantly in magnitude and periodically in direction.
Larger than that found in the primary winding.
A.C.
Squirrel-cage rotor.

46. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
5:1.
Inductance.
The chest should rise or inflate.
Tied together

47. The primary leads of a single-phase transformer should be connected to the...
H terminals.
Draw less current.
800 volts.
Isolation transformer.

48. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Second-degree burn.
Continuous.
Four times less than that of the secondary.
X.

49. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
A step-up transformer.
3 -979 Volts.
A device used to store electrical energy.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

50. What type of 3-phase AC motor is used most often around a mine?
Kilovolt ampere (KVA).
Circuit Breaker.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Squirrel-cage induction motor.