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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...
7 -630 volts.
Draw less current.
5:1.
5:1

2. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
A grounding resistor.
Four times less than that of the secondary.
No.6 AWG.
An electrical shock hazard may exist.

3. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
H terminals.
Transformer
Provides single-phase power to smaller loads such as lights - heaters - etc.

4. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
An electrical shock hazard may exist.
The chest should rise or inflate.
Shunted and taped
X.

5. Operating coils - motors - transformers - relays and solenoids depend upon...
Draw less current.
The sum of the two capacitors.
Isolation transformer.
Electro-magnetism for their operation.

6. 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?
800 volts.
75 turns.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
5:1.

7. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Check to make sure that the victim is not still in contact with the electricity.
The capacitors should be discharged.
At least two phases
Inductance.

8. If any two-phase wires are reversed on a three-phase motor - the motor will...
The chest should rise or inflate.
Inductance.
Reverse its rotation.
800 volts.

9. A wound-rotor induction motor has all the following EXCEPT...
75 turns.
480 volts.
X.
Squirrel-cage rotor.

10. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
Lower current and higher voltage.
Grounded phase and ground fault devices were not operating.
Derive a neutral for grounding purposes.

11. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Four times less than that of the secondary.
Capacitance.
800 volts.
The chest should rise or inflate.

12. Not a symptom of electrical shock?.
A device used to store electrical energy.
Hyperventilation.
Inductance.
100 volts.

13. Three-phase AC underground cables must be provided with overcurrent protection using a...
Nearly constant.
Circuit Breaker.
Current changing constantly in magnitude and periodically in direction.
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?
They should be made by the same manufacturer.
Because less current flowing at high voltage causes less line loss per kilowatt.
200 volts AC.
600 volts.

15. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
A step-up transformer.
2000 watts
Short-circuited after power has been removed.
A.C.

16. What type motor is a wound-rotor induction motor?
A grounding resistor.
Two speeds
Zero amps.
A.C.

17. Current that changes periodically in direction is...
Alternating current.
600 volts.
Check to make sure that the victim is not still in contact with the electricity.
They must be installed at least 7 feet above the ground.

18. What is the danger when working around capacitors?
Allow for metering voltage and Current.
An electrical shock hazard may exist.
The sum of the two capacitors.
The motor rotation is reversed.

19. The main function of CT's and PT's on a main substation is to...
Continuous.
100 volts.
60 cycles per second (60 Hertz).
Allow for metering voltage and Current.

20. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The motor rotation is reversed.
No.6 AWG.
The current will read zero.
Disconnect the frame-grounding conductor.

21. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
100 turns.
5:1
7 -630 volts.
Reverse any two-phase leads.

22. AC voltage is raised or lowered by means of...
They must be installed at least 7 feet above the ground.
The current will read zero.
1 amp.
Transformers.

23. 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...
Transformer
Tied together
Lower current and higher voltage
480 volts.

24. The combined capacitance of two capacitors in parallel is...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
H terminals.
The sum of the two capacitors.

25. 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?
Clamp-on ammeter.
75 turns.
Disconnect the frame-grounding conductor.
150 turns.

26. The speed of an alternating current - squirrel-cage induction motor is...
The motor rotation is reversed.
Shunted and taped
Circuit Breaker.
Nearly constant.

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?
Short-circuited after power has been removed.
100 turns.
25 feet.
The chest should rise or inflate.

28. The transformer used only to measure voltage is a...
Carotid pulse - which is located in the neck next to the Adam's apple.
Capacitance.
At least two phases
Potential transformer.

29. A control power transformer...
H terminals.
Inductance.
Provides single-phase power to smaller loads such as lights - heaters - etc.
277 volts.

30. Compared to the secondary of a loaded - step-down transformer - the primary has...
Stator windings.
Lower current and higher voltage
2000 watts
480 volts.

31. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Transformer
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The motor rotation is reversed.

32. 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...
Draw less current.
100 volts.
At the source transformer.
3 -979 Volts.

33. When not connected to a load - the secondary leads of a current transformer should be...
Inductance.
25 feet.
Shunted and taped
60 Hertz

34. The standard frequency of power supplied by the power company is...
Capacitance.
Carotid pulse - which is located in the neck next to the Adam's apple.
A step-up transformer.
60 cycles per second (60 Hertz).

35. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Squirrel-cage rotor.
The current will read zero.
150 turns.
Four times less than that of the secondary.

36. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
600 volts.
Draw less current.
Nearly constant.
Two speeds

37. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Squirrel-cage induction motor.
1 amp.
An electromagnet.

38. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
Inductance.
Allow for metering voltage and Current.
Current changing constantly in magnitude and periodically in direction.

39. 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.
480 volts.
Hyperventilation.
5:1.
60 cycles per second (60 Hertz).

40. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
480 volts.
It provides good speed control.
The chest should rise or inflate.
Grounded phase and ground fault devices were not operating.

41. 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?
Stator windings.
Current changing constantly in magnitude and periodically in direction.
Four times less than that of the secondary.
800 volts.

42. 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.
Continuous.
They should be made by the same manufacturer.
Capacitance.

43. Which of the following does a squirrel cage induction motor have?
Second-degree burn.
Current that changes constantly in magnitude and periodically in direction.
Stator windings.
Squirrel-cage induction motor.

44. The property of an electric circuit that opposes any change in current is called...
Inductance.
At least two phases
Provides single-phase power to smaller loads such as lights - heaters - etc.
75 turns.

45. The size of a transformer is measured in...
Full-load - three-phase voltage.
100 volts.
Kilovolt ampere (KVA).
12 to 15 times a minute.

46. A burn causing a blister is classified as a...
It provides good speed control.
Second-degree burn.
Kilovolt ampere (KVA).
Draw less current.

47. High voltage is used to transmit power over long distances...
A grounding resistor.
Clamp-on ammeter.
Larger than that found in the primary winding.
Because less current flowing at high voltage causes less line loss per kilowatt.

48. 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.
Cut around clothing that has adhered to the burned area.
5:1
Current changing constantly in magnitude and periodically in direction.
Draw less current.

49. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Circuit Breaker.
5:1
Draw less current.
480 volts.

50. Not an acceptable method for the installations of surface transformers?
Lower current and higher voltage
800 volts.
They must be installed at least 7 feet above the ground.
X.