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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. 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?
Alternating current.
5:1.
Lower current and higher voltage.
600 volts.

2. 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?
75 turns.
Squirrel-cage induction motor.
Capacitance.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

3. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
No.6 AWG.
A step-up transformer.
Check to make sure that the victim is not still in contact with the electricity.

4. 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
Nearly constant.
75 turns.
100 volts.

5. 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.
Short-circuited after power has been removed.
Allow for metering voltage and Current.
12 to 15 times a minute.

6. Not a symptom of electrical shock?.
Hyperventilation.
Squirrel-cage rotor.
It provides good speed control.
75 turns.

7. A transformer with a 1:1 ratio is usually a (an)...
Transformer
Because less current flowing at high voltage causes less line loss per kilowatt.
The motor rotation is reversed.
Isolation transformer.

8. How do you change the direction of a 3-phase AC motor?
Isolation transformer.
Reverse any two-phase leads.
Reverse its rotation.
Disconnect the frame-grounding conductor.

9. High voltage is used to transmit power over long distances...
Allow for metering voltage and Current.
Draw less current.
Because less current flowing at high voltage causes less line loss per kilowatt.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

10. The primary function of a power transformer is to provide...
Allow for metering voltage and Current.
Full-load - three-phase voltage.
Kilovolt ampere (KVA).
Short-circuited after power has been removed.

11. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
15 feet off the ground.
Larger than that found in the primary winding.
3 -979 Volts.

12. 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.
75 turns.
Zero amps.
Squirrel-cage induction motor.

13. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
12 to 15 times a minute.
Disconnect the frame-grounding conductor.
Stator windings.
Carotid pulse - which is located in the neck next to the Adam's apple.

14. What steps up or steps down AC voltage?
Transformer
75 turns.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Potential transformer.

15. The primary leads of a single-phase transformer should be connected to the...
2000 watts
H terminals.
15 feet off the ground.
Isolation transformer.

16. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
25 feet.
Tied together
Short-circuited after power has been removed.
At the source transformer.

17. 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?
Transformer
Disconnect the frame-grounding conductor.
150 turns.
60 Hertz

18. Three-phase AC underground cables must be provided with overcurrent protection using a...
Short-circuited after power has been removed.
Capacitance.
Current changing constantly in magnitude and periodically in direction.
Circuit Breaker.

19. When not connected to a load - the secondary leads of a current transformer should be...
15 feet off the ground.
Second-degree burn.
Alternating current.
Shunted and taped

20. Current that changes periodically in direction is...
Potential transformer.
Tied together
Zero amps.
Alternating current.

21. 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.
Check to make sure that the victim is not still in contact with the electricity.
Circuit Breaker.
Full-load - three-phase voltage.

22. 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.
They should be made by the same manufacturer.
Nearly constant.
2000 watts
5:1

23. Which of the following does a squirrel cage induction motor have?
Because less current flowing at high voltage causes less line loss per kilowatt.
Lower current and higher voltage.
Stator windings.
X.

24. The property of an electric circuit that opposes any change in current is called...
Disconnect the frame-grounding conductor.
Full-load - three-phase voltage.
Potential transformer.
Inductance.

25. How should clothing be removed from a burn?
5:1
Cut around clothing that has adhered to the burned area.
Because less current flowing at high voltage causes less line loss per kilowatt.
Two speeds

26. 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.
The capacitors should be discharged.
X.
800 volts.

27. A wound-rotor induction motor has all the following EXCEPT...
Potential transformer.
It provides good speed control.
Squirrel-cage rotor.
Short-circuited after power has been removed.

28. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
A grounding resistor.
150 turns.
At least two phases

29. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
5:1.
No.6 AWG.
200 volts AC.
The current will read zero.

30. What is the first step to be followed in aiding a victim of electrical shock?
150 turns.
7 -630 volts.
75 turns.
Check to make sure that the victim is not still in contact with the electricity.

31. 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?
The capacitors should be discharged.
Four times less than that of the secondary.
200 volts AC.
5:1.

32. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Grounded phase and ground fault devices were not operating.
7 -630 volts.
Hyperventilation.

33. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because less current flowing at high voltage causes less line loss per kilowatt.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Derive a neutral for grounding purposes.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

34. What type motor is a wound-rotor induction motor?
Squirrel-cage rotor.
Transformers.
Because less current flowing at high voltage causes less line loss per kilowatt.
A.C.

35. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
The sum of the two capacitors.
H terminals.
They should be made by the same manufacturer.
Zero amps.

36. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
At the source transformer.
2000 watts
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The chest should rise or inflate.

37. What is the danger when working around capacitors?
Draw less current.
An electrical shock hazard may exist.
Circuit Breaker.
Tied together

38. AC voltage is raised or lowered by means of...
150 turns.
Inductance.
Transformers.
H terminals.

39. The purpose of a zig-zag transformer is to...
Draw less current.
Squirrel-cage induction motor.
Derive a neutral for grounding purposes.
Inductance.

40. What is a capacitor?
The current will read zero.
An electromagnet.
1 amp.
A device used to store electrical energy.

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...
Capacitance.
Tied together
Draw less current.
Second-degree burn.

42. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Continuous.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Reverse its rotation.

43. Not an acceptable method for the installations of surface transformers?
2000 watts
They must be installed at least 7 feet above the ground.
5:1
277 volts.

44. The property of an electrical circuit that opposes any change in voltage is called...
Clamp-on ammeter.
Kilovolt ampere (KVA).
7 -630 volts.
Capacitance.

45. The size of a transformer is measured in...
Transformer
Capacitance.
An electromagnet.
Kilovolt ampere (KVA).

46. The standard frequency of power supplied by the power company is...
Carotid pulse - which is located in the neck next to the Adam's apple.
Reverse any two-phase leads.
7 -630 volts.
60 cycles per second (60 Hertz).

47. 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.
Capacitance.
At the source transformer.
Potential transformer.

48. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.
The current will read zero.
Clamp-on ammeter.

49. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
Zero amps.
Capacitance.
Transformers.

50. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
Draw less current.
Four times less than that of the secondary.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.