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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. The purpose of a zig-zag transformer is to...
At the source transformer.
Draw less current.
Derive a neutral for grounding purposes.
Current changing constantly in magnitude and periodically in direction.

2. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
A.C.
Shunted and taped
25 feet.
800 volts.

3. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
They should be made by the same manufacturer.
75 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.

4. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
Allow for metering voltage and Current.
480 volts.
A step-up transformer.

5. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Hyperventilation.
277 volts.
Current that changes constantly in magnitude and periodically in direction.
1 amp.

6. 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...
Circuit Breaker.
Carotid pulse - which is located in the neck next to the Adam's apple.
Draw less current.
Zero amps.

7. 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?
Two speeds
Hyperventilation.
25 feet.
100 turns.

8. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Shunted and taped
Squirrel-cage induction motor.
The motor rotation is reversed.
480 volts.

9. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
5:1
Clamp-on ammeter.
No.6 AWG.
200 volts AC.

10. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
An electromagnet.
Continuous.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Transformer

11. Operating coils - motors - transformers - relays and solenoids depend upon...
5:1.
At the source transformer.
Hyperventilation.
Electro-magnetism for their operation.

12. 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.
1 amp.
The chest should rise or inflate.
At the source transformer.

13. What is a capacitor?
A grounding resistor.
Lower current and higher voltage
A device used to store electrical energy.
They should be made by the same manufacturer.

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

15. How do you change the direction of a 3-phase AC motor?
Stator windings.
Reverse any two-phase leads.
7 -630 volts.
2000 watts

16. What should the duty rating of a grounding resistor be?
Four times less than that of the secondary.
Continuous.
H terminals.
Carotid pulse - which is located in the neck next to the Adam's apple.

17. 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 Hertz
Carotid pulse - which is located in the neck next to the Adam's apple.
200 volts AC.
25 feet.

18. All transformers step voltage up or down by...
Full-load - three-phase voltage.
Inductance.
Squirrel-cage induction motor.
Nearly constant.

19. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Disconnect the frame-grounding conductor.
60 Hertz
2000 watts
Tied together

20. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
The chest should rise or inflate.
480 volts.
Lower current and higher voltage

21. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Carotid pulse - which is located in the neck next to the Adam's apple.
They should be made by the same manufacturer.
Disconnect the frame-grounding conductor.
7 -630 volts.

22. A transformer with a 1:1 ratio is usually a (an)...
Grounded phase and ground fault devices were not operating.
Stator windings.
Isolation transformer.
Potential transformer.

23. 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?
Two speeds
75 turns.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

24. A control power transformer...
800 volts.
Four times less than that of the secondary.
Nearly constant.
Provides single-phase power to smaller loads such as lights - heaters - etc.

25. 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...
Zero amps.
3 -979 Volts.
Draw less current.
Transformers.

26. AC voltage is raised or lowered by means of...
Kilovolt ampere (KVA).
Current that changes constantly in magnitude and periodically in direction.
Transformers.
At the source transformer.

27. Not true about AC power?
Second-degree burn.
It provides good speed control.
800 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

28. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
5:1.
No.6 AWG.
3 -979 Volts.

29. 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.
The sum of the two capacitors.
150 turns.
5:1.
At least two phases

30. 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?
Capacitance.
3 -979 Volts.
Isolation transformer.
Continuous.

31. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
7 -630 volts.
Clamp-on ammeter.
Squirrel-cage induction motor.
The capacitors should be discharged.

32. The primary function of a power transformer is to provide...
Check to make sure that the victim is not still in contact with the electricity.
Full-load - three-phase voltage.
At least two phases
The capacitors should be discharged.

33. 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.
Cut around clothing that has adhered to the burned area.
Current changing constantly in magnitude and periodically in direction.
800 volts.

34. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
100 turns.
Zero amps.
The chest should rise or inflate.

35. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
75 turns.
It provides good speed control.
X.
Nearly constant.

36. Current that changes periodically in direction is...
H terminals.
Capacitance.
Reverse any two-phase leads.
Alternating current.

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

38. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
7 -630 volts.
Disconnect the frame-grounding conductor.
Electro-magnetism for their operation.
15 feet off the ground.

39. A burn causing a blister is classified as a...
Second-degree burn.
Potential transformer.
Current that changes constantly in magnitude and periodically in direction.
The motor rotation is reversed.

40. 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.
Isolation transformer.
150 turns.
Second-degree burn.

41. Compared to the secondary of a loaded - step-down transformer - the primary has...
Current that changes constantly in magnitude and periodically in direction.
Lower current and higher voltage
Alternating current.
Lower current and higher voltage.

42. Current in an AC circuit may be measured by...
Nearly constant.
Clamp-on ammeter.
They must be installed at least 7 feet above the ground.
Squirrel-cage rotor.

43. 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.
The current will read zero.
200 volts AC.

44. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
They should be made by the same manufacturer.
5:1
Inductance.

45. 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...
It provides good speed control.
Tied together
Full-load - three-phase voltage.
60 Hertz

46. Where should grounding resistors be located?
Potential transformer.
At the source transformer.
3 -979 Volts.
Because less current flowing at high voltage causes less line loss per kilowatt.

47. Define alternating current...
5:1.
Current changing constantly in magnitude and periodically in direction.
Inductance.
800 volts.

48. The combined capacitance of two capacitors in parallel is...
At the source transformer.
800 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The sum of the two capacitors.

49. The property of an electric circuit that opposes any change in current is called...
Squirrel-cage induction motor.
Inductance.
The chest should rise or inflate.
Continuous.

50. 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?
600 volts.
Zero amps.
It provides good speed control.
12 to 15 times a minute.