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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 property of an electrical circuit that opposes any change in voltage is called...
The current will read zero.
The motor rotation is reversed.
Capacitance.
75 turns.

2. Alternating current may be defined as...
100 turns.
Current that changes constantly in magnitude and periodically in direction.
Carotid pulse - which is located in the neck next to the Adam's apple.
Circuit Breaker.

3. High voltage is used to transmit power over long distances...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
5:1
Because less current flowing at high voltage causes less line loss per kilowatt.
Current changing constantly in magnitude and periodically in direction.

4. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
A.C.
Transformers.
The motor rotation is reversed.
H terminals.

5. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Check to make sure that the victim is not still in contact with the electricity.
Draw less current.
Disconnect the frame-grounding conductor.
100 volts.

6. Compared to the secondary of a loaded - step-down transformer - the primary has...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
5:1
Lower current and higher voltage
H terminals.

7. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Nearly constant.
Zero amps.
100 volts.
The sum of the two capacitors.

8. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
60 cycles per second (60 Hertz).
Inductance.
Current that changes constantly in magnitude and periodically in direction.

9. When not connected to a load - the secondary leads of a current transformer should be...
Cut around clothing that has adhered to the burned area.
Shunted and taped
They should be made by the same manufacturer.
5:1.

10. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Inductance.
At least two phases
The current will read zero.
A step-up transformer.

11. Not an acceptable method for the installations of surface transformers?
They should be made by the same manufacturer.
Because less current flowing at high voltage causes less line loss per kilowatt.
H terminals.
They must be installed at least 7 feet above the ground.

12. What is the first step to be followed in aiding a victim of electrical shock?
Kilovolt ampere (KVA).
Check to make sure that the victim is not still in contact with the electricity.
3 -979 Volts.
Second-degree burn.

13. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
60 cycles per second (60 Hertz).
Transformer
Zero amps.

14. The secondary windings on a 10:1 step-down transformer will have a wire size...
A.C.
Larger than that found in the primary winding.
5:1.
Cut around clothing that has adhered to the burned area.

15. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Squirrel-cage induction motor.
15 feet off the ground.
25 feet.
Inductance.

16. The property of an electric circuit that opposes any change in current is called...
A device used to store electrical energy.
Inductance.
Full-load - three-phase voltage.
12 to 15 times a minute.

17. How do you change the direction of a 3-phase AC motor?
Potential transformer.
An electromagnet.
Reverse any two-phase leads.
Inductance.

18. 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.
Grounded phase and ground fault devices were not operating.
At least two phases
100 turns.

19. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
Provides single-phase power to smaller loads such as lights - heaters - etc.
The motor rotation is reversed.
2000 watts

20. A transformer with a 1:1 ratio is usually a (an)...
Inductance.
Isolation transformer.
Shunted and taped
Alternating current.

21. All transformers step voltage up or down by...
The motor rotation is reversed.
Transformer
Inductance.
It provides good speed control.

22. The standard frequency of power supplied by the power company is...
Squirrel-cage rotor.
1 amp.
60 cycles per second (60 Hertz).
Zero amps.

23. The size of a transformer is measured in...
The sum of the two capacitors.
Hyperventilation.
Kilovolt ampere (KVA).
A step-up transformer.

24. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Larger than that found in the primary winding.
Four times less than that of the secondary.
480 volts.
2000 watts

25. Define alternating current...
H terminals.
75 turns.
Current changing constantly in magnitude and periodically in direction.
A.C.

26. Not true about AC power?
Second-degree burn.
Two speeds
Carotid pulse - which is located in the neck next to the Adam's apple.
It provides good speed control.

27. The primary leads of a single-phase transformer should be connected to the...
Cut around clothing that has adhered to the burned area.
100 volts.
At least two phases
H terminals.

28. 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
Continuous.
Squirrel-cage induction motor.
Transformers.

29. If any two-phase wires are reversed on a three-phase motor - the motor will...
They must be installed at least 7 feet above the ground.
75 turns.
480 volts.
Reverse its rotation.

30. What type motor is a wound-rotor induction motor?
A.C.
A grounding resistor.
Reverse any two-phase leads.
5:1

31. The speed of an alternating current - squirrel-cage induction motor is...
1 amp.
15 feet off the ground.
Nearly constant.
Zero amps.

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.
Larger than that found in the primary winding.
Transformer
5:1

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.
At the source transformer.
Two speeds
Zero amps.

34. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Short-circuited after power has been removed.
150 turns.
An electrical shock hazard may exist.

35. 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.
12 to 15 times a minute.
5:1.
At least two phases

36. The combined capacitance of two capacitors in parallel is...
5:1
The current will read zero.
The sum of the two capacitors.
75 turns.

37. What is the danger when working around capacitors?
Check to make sure that the victim is not still in contact with the electricity.
An electrical shock hazard may exist.
Squirrel-cage induction motor.
Disconnect the frame-grounding conductor.

38. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Lower current and higher voltage
7 -630 volts.
Reverse any two-phase leads.
X.

39. Operating coils - motors - transformers - relays and solenoids depend upon...
150 turns.
Reverse any two-phase leads.
The sum of the two capacitors.
Electro-magnetism for their operation.

40. A solenoid coil is...
Capacitance.
Draw less current.
An electromagnet.
Carotid pulse - which is located in the neck next to the Adam's apple.

41. 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...
Derive a neutral for grounding purposes.
Full-load - three-phase voltage.
Second-degree burn.
Draw less current.

42. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
12 to 15 times a minute.
A device used to store electrical energy.
The motor rotation is reversed.

43. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
25 feet.
Stator windings.
600 volts.
1 amp.

44. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Squirrel-cage induction motor.
15 feet off the ground.
Reverse any two-phase leads.
Four times less than that of the secondary.

45. Compared to the secondary of a loaded - step-down transformer - the primary has...
Cut around clothing that has adhered to the burned area.
Lower current and higher voltage.
Because less current flowing at high voltage causes less line loss per kilowatt.
Inductance.

46. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Hyperventilation.
Zero amps.
Reverse any two-phase leads.
A step-up transformer.

47. 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?
Capacitance.
75 turns.
600 volts.
A grounding resistor.

48. Which of the following does a squirrel cage induction motor have?
75 turns.
Stator windings.
Full-load - three-phase voltage.
Larger than that found in the primary winding.

49. At what rate should mouth-to-mouth resuscitation be applied?
Provides single-phase power to smaller loads such as lights - heaters - etc.
12 to 15 times a minute.
Kilovolt ampere (KVA).
800 volts.

50. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
15 feet off the ground.
Squirrel-cage induction motor.
12 to 15 times a minute.
480 volts.