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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. 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...
2000 watts
Reverse its rotation.
Draw less current.
Carotid pulse - which is located in the neck next to the Adam's apple.

2. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
15 feet off the ground.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
480 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.

3. 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.
Lower current and higher voltage
Zero amps.

4. 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...
Draw less current.
7 -630 volts.
Lower current and higher voltage.
The sum of the two capacitors.

5. The size of a transformer is measured in...
Alternating current.
Kilovolt ampere (KVA).
The current will read zero.
The motor rotation is reversed.

6. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
An electrical shock hazard may exist.
The capacitors should be discharged.
X.
Capacitance.

7. What should the duty rating of a grounding resistor be?
75 turns.
Continuous.
Electro-magnetism for their operation.
60 Hertz

8. A control power transformer...
Alternating current.
Potential transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
75 turns.

9. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
Reverse any two-phase leads.
100 volts.
Current that changes constantly in magnitude and periodically in direction.

10. The primary leads of a single-phase transformer should be connected to the...
H terminals.
Squirrel-cage induction motor.
3 -979 Volts.
Reverse its rotation.

11. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Clamp-on ammeter.
277 volts.
An electrical shock hazard may exist.
Short-circuited after power has been removed.

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

13. At what rate should mouth-to-mouth resuscitation be applied?
Squirrel-cage induction motor.
277 volts.
Cut around clothing that has adhered to the burned area.
12 to 15 times a minute.

14. The purpose of a zig-zag transformer is to...
75 turns.
Squirrel-cage rotor.
Derive a neutral for grounding purposes.
Provides single-phase power to smaller loads such as lights - heaters - etc.

15. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Transformer
60 cycles per second (60 Hertz).
Disconnect the frame-grounding conductor.
Larger than that found in the primary winding.

16. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
5:1.
Hyperventilation.
Inductance.
Zero amps.

17. A solenoid coil is...
60 Hertz
An electromagnet.
60 cycles per second (60 Hertz).
It provides good speed control.

18. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Reverse any two-phase leads.
Inductance.
The motor rotation is reversed.
15 feet off the ground.

19. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The motor rotation is reversed.
Inductance.
The current will read zero.
12 to 15 times a minute.

20. Which of the following does a squirrel cage induction motor have?
No.6 AWG.
Zero amps.
Stator windings.
60 Hertz

21. 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.
5:1.
A grounding resistor.
Lower current and higher voltage.
Nearly constant.

22. 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...
Carotid pulse - which is located in the neck next to the Adam's apple.
Tied together
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Squirrel-cage induction motor.

23. 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.
The capacitors should be discharged.
Lower current and higher voltage.
Current that changes constantly in magnitude and periodically in direction.
5:1

24. What is a capacitor?
Full-load - three-phase voltage.
A device used to store electrical energy.
Inductance.
Squirrel-cage induction motor.

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?
Carotid pulse - which is located in the neck next to the Adam's apple.
100 turns.
Shunted and taped
Four times less than that of the secondary.

26. The standard frequency of alternating current used at a mine is...
480 volts.
Inductance.
60 Hertz
X.

27. The combined capacitance of two capacitors in parallel is...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Reverse its rotation.
150 turns.
The sum of the two capacitors.

28. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
5:1.
2000 watts
3 -979 Volts.

29. The standard frequency of power supplied by the power company is...
The current will read zero.
60 cycles per second (60 Hertz).
Electro-magnetism for their operation.
An electromagnet.

30. A burn causing a blister is classified as a...
Transformers.
Reverse its rotation.
Second-degree burn.
An electromagnet.

31. The transformer used only to measure voltage is a...
A step-up transformer.
Lower current and higher voltage
Alternating current.
Potential transformer.

32. The speed of an alternating current - squirrel-cage induction motor is...
Lower current and higher voltage.
Derive a neutral for grounding purposes.
60 Hertz
Nearly constant.

33. 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.
1 amp.
Kilovolt ampere (KVA).
A device used to store electrical energy.

34. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
A device used to store electrical energy.
Transformers.
800 volts.
The chest should rise or inflate.

35. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
The motor rotation is reversed.
The current will read zero.
Draw less current.

36. 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?
Draw less current.
12 to 15 times a minute.
Transformer
200 volts AC.

37. The main function of CT's and PT's on a main substation is to...
A.C.
Current changing constantly in magnitude and periodically in direction.
480 volts.
Allow for metering voltage and Current.

38. A transformer with a 1:1 ratio is usually a (an)...
7 -630 volts.
A step-up transformer.
Isolation transformer.
At the source transformer.

39. What type of 3-phase AC motor is used most often around a mine?
200 volts AC.
H terminals.
Squirrel-cage induction motor.
X.

40. 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?
Hyperventilation.
Transformers.
No.6 AWG.
800 volts.

41. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Potential transformer.
Transformers.
Carotid pulse - which is located in the neck next to the Adam's apple.
No.6 AWG.

42. High voltage is used to transmit power over long distances...
Isolation transformer.
Squirrel-cage induction motor.
Because less current flowing at high voltage causes less line loss per kilowatt.
60 Hertz

43. Not true about AC power?
3 -979 Volts.
H terminals.
It provides good speed control.
75 turns.

44. A wound-rotor induction motor has all the following EXCEPT...
An electromagnet.
Squirrel-cage rotor.
277 volts.
A step-up transformer.

45. What type motor is a wound-rotor induction motor?
Circuit Breaker.
Cut around clothing that has adhered to the burned area.
A.C.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

46. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
The motor rotation is reversed.
7 -630 volts.
Allow for metering voltage and Current.
600 volts.

47. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Nearly constant.
Carotid pulse - which is located in the neck next to the Adam's apple.
Two speeds
The motor rotation is reversed.

48. AC voltage is raised or lowered by means of...
Transformers.
Draw less current.
At least two phases
Transformer

49. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
The current will read zero.
Potential transformer.
A grounding resistor.
X.

50. All transformers step voltage up or down by...
Continuous.
Cut around clothing that has adhered to the burned area.
Lower current and higher voltage
Inductance.