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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. Alternating current may be defined as...
They should be made by the same manufacturer.
Hyperventilation.
Current that changes constantly in magnitude and periodically in direction.
Shunted and taped

2. 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...
Four times less than that of the secondary.
Draw less current.
5:1
An electrical shock hazard may exist.

3. To protect against over-current in a three-phase circuit over-current protection must be provided for...
200 volts AC.
Shunted and taped
At least two phases
5:1

4. A wound-rotor induction motor has all the following EXCEPT...
60 cycles per second (60 Hertz).
The current will read zero.
Squirrel-cage rotor.
Transformers.

5. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Squirrel-cage induction motor.
277 volts.
200 volts AC.
Two speeds

6. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Full-load - three-phase voltage.
Grounded phase and ground fault devices were not operating.
A step-up transformer.
Kilovolt ampere (KVA).

7. High voltage is used to transmit power over long distances...
H terminals.
Because less current flowing at high voltage causes less line loss per kilowatt.
Clamp-on ammeter.
Shunted and taped

8. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
An electromagnet.
15 feet off the ground.
Derive a neutral for grounding purposes.

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

10. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Four times less than that of the secondary.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
480 volts.
Zero amps.

11. Which of the following does a squirrel cage induction motor have?
5:1.
Full-load - three-phase voltage.
Stator windings.
12 to 15 times a minute.

12. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Cut around clothing that has adhered to the burned area.
25 feet.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Draw less current.

13. All transformers step voltage up or down by...
Inductance.
5:1.
H terminals.
Allow for metering voltage and Current.

14. 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?
Zero amps.
200 volts AC.
800 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

15. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
Continuous.
60 cycles per second (60 Hertz).
100 volts.

16. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Current changing constantly in magnitude and periodically in direction.
Cut around clothing that has adhered to the burned area.
480 volts.
Two speeds

17. Define alternating current...
X.
Current changing constantly in magnitude and periodically in direction.
Disconnect the frame-grounding conductor.
Lower current and higher voltage.

18. 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?
Potential transformer.
800 volts.
Continuous.
Current that changes constantly in magnitude and periodically in direction.

19. The size of a transformer is measured in...
Kilovolt ampere (KVA).
Lower current and higher voltage.
12 to 15 times a minute.
800 volts.

20. The standard frequency of power supplied by the power company is...
Inductance.
60 cycles per second (60 Hertz).
Transformer
Second-degree burn.

21. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
A device used to store electrical energy.
Carotid pulse - which is located in the neck next to the Adam's apple.
The chest should rise or inflate.

22. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Reverse its rotation.
Squirrel-cage induction motor.
The sum of the two capacitors.

23. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Grounded phase and ground fault devices were not operating.
25 feet.
100 volts.
Kilovolt ampere (KVA).

24. A control power transformer...
Continuous.
A device used to store electrical energy.
Draw less current.
Provides single-phase power to smaller loads such as lights - heaters - etc.

25. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The current will read zero.
Capacitance.
Stator windings.
3 -979 Volts.

26. 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.
5:1
Potential transformer.
Squirrel-cage rotor.
Stator windings.

27. 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.
The capacitors should be discharged.
25 feet.
480 volts.

28. The secondary windings on a 10:1 step-down transformer will have a wire size...
No.6 AWG.
100 turns.
Larger than that found in the primary winding.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

29. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Transformers.
Because less current flowing at high voltage causes less line loss per kilowatt.
An electromagnet.
A grounding resistor.

30. 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.
Nearly constant.
Lower current and higher voltage.
5:1.
Squirrel-cage rotor.

31. What is the danger when working around capacitors?
2000 watts
Two speeds
Squirrel-cage rotor.
An electrical shock hazard may exist.

32. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Grounded phase and ground fault devices were not operating.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Continuous.
X.

33. Not a symptom of electrical shock?.
Cut around clothing that has adhered to the burned area.
Current that changes constantly in magnitude and periodically in direction.
Hyperventilation.
Lower current and higher voltage.

34. Current in an AC circuit may be measured by...
Derive a neutral for grounding purposes.
The current will read zero.
Clamp-on ammeter.
Reverse its rotation.

35. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Inductance.
2000 watts
Transformer
Grounded phase and ground fault devices were not operating.

36. What is a capacitor?
A device used to store electrical energy.
1 amp.
Nearly constant.
Carotid pulse - which is located in the neck next to the Adam's apple.

37. 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...
Tied together
Derive a neutral for grounding purposes.
The capacitors should be discharged.
An electromagnet.

38. The purpose of a zig-zag transformer is to...
They should be made by the same manufacturer.
Current that changes constantly in magnitude and periodically in direction.
Derive a neutral for grounding purposes.
Larger than that found in the primary winding.

39. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
60 Hertz
Stator windings.
7 -630 volts.
75 turns.

40. A solenoid coil is...
An electromagnet.
The sum of the two capacitors.
At the source transformer.
A.C.

41. The main function of CT's and PT's on a main substation is to...
25 feet.
Potential transformer.
Allow for metering voltage and Current.
At the source transformer.

42. 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.
60 Hertz
800 volts.
150 turns.

43. When not connected to a load - the secondary leads of a current transformer should be...
1 amp.
Short-circuited after power has been removed.
Transformer
Shunted and taped

44. If any two-phase wires are reversed on a three-phase motor - the motor will...
Transformers.
12 to 15 times a minute.
Reverse its rotation.
Capacitance.

45. 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.
Grounded phase and ground fault devices were not operating.
Reverse its rotation.
Disconnect the frame-grounding conductor.

46. AC voltage is raised or lowered by means of...
A grounding resistor.
It provides good speed control.
They should be made by the same manufacturer.
Transformers.

47. Not an acceptable method for the installations of surface transformers?
Lower current and higher voltage
They must be installed at least 7 feet above the ground.
Four times less than that of the secondary.
Zero amps.

48. 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?
Second-degree burn.
At the source transformer.
Allow for metering voltage and Current.
75 turns.

49. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Lower current and higher voltage
The capacitors should be discharged.
Inductance.
Two speeds

50. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
277 volts.
At the source transformer.
The motor rotation is reversed.
No.6 AWG.