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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. 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.
200 volts AC.
The current will read zero.
100 volts.

2. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
A device used to store electrical energy.
Short-circuited after power has been removed.
60 cycles per second (60 Hertz).
The chest should rise or inflate.

3. Operating coils - motors - transformers - relays and solenoids depend upon...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
60 cycles per second (60 Hertz).
Electro-magnetism for their operation.
Stator windings.

4. The transformer used only to measure voltage is a...
Two speeds
277 volts.
Kilovolt ampere (KVA).
Potential transformer.

5. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
600 volts.
Grounded phase and ground fault devices were not operating.
Electro-magnetism for their operation.

6. The primary leads of a single-phase transformer should be connected to the...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Short-circuited after power has been removed.
H terminals.
They must be installed at least 7 feet above the ground.

7. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
60 cycles per second (60 Hertz).
A grounding resistor.
The capacitors should be discharged.
Potential transformer.

8. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
A device used to store electrical energy.
Two speeds
100 turns.

9. 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.
1 amp.
Second-degree burn.
An electrical shock hazard may exist.

10. Define alternating current...
Stator windings.
Potential transformer.
Second-degree burn.
Current changing constantly in magnitude and periodically in direction.

11. The property of an electric circuit that opposes any change in current is called...
60 cycles per second (60 Hertz).
Four times less than that of the secondary.
A grounding resistor.
Inductance.

12. Compared to the secondary of a loaded - step-down transformer - the primary has...
15 feet off the ground.
Lower current and higher voltage
Nearly constant.
75 turns.

13. 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?
A step-up transformer.
600 volts.
Hyperventilation.
75 turns.

14. Not an acceptable method for the installations of surface transformers?
Second-degree burn.
They must be installed at least 7 feet above the ground.
Derive a neutral for grounding purposes.
Inductance.

15. Current that changes periodically in direction is...
Grounded phase and ground fault devices were not operating.
Alternating current.
They must be installed at least 7 feet above the ground.
60 Hertz

16. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Larger than that found in the primary winding.
Nearly constant.
Zero amps.
Potential transformer.

17. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Allow for metering voltage and Current.
100 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.

18. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
277 volts.
No.6 AWG.
Hyperventilation.
The chest should rise or inflate.

19. 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?
Derive a neutral for grounding purposes.
Second-degree burn.
75 turns.
Transformer

20. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Shunted and taped
60 Hertz
X.
Clamp-on ammeter.

21. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Zero amps.
An electromagnet.
At least two phases
Tied together

22. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Reverse any two-phase leads.
277 volts.
They should be made by the same manufacturer.
They must be installed at least 7 feet above the ground.

23. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
5:1
Isolation transformer.
Current changing constantly in magnitude and periodically in direction.
The chest should rise or inflate.

24. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
2000 watts
15 feet off the ground.
Circuit Breaker.
Tied together

25. What type motor is a wound-rotor induction motor?
5:1
25 feet.
A.C.
5:1.

26. 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?
75 turns.
12 to 15 times a minute.
200 volts AC.
Reverse any two-phase leads.

27. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
7 -630 volts.
25 feet.
Alternating current.
150 turns.

28. Which of the following does a squirrel cage induction motor have?
Circuit Breaker.
Capacitance.
75 turns.
Stator windings.

29. If any two-phase wires are reversed on a three-phase motor - the motor will...
Alternating current.
Circuit Breaker.
Reverse its rotation.
Inductance.

30. Alternating current may be defined as...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Current that changes constantly in magnitude and periodically in direction.
25 feet.
200 volts AC.

31. 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...
Tied together
Circuit Breaker.
Potential transformer.
Draw less current.

32. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
60 Hertz
15 feet off the ground.
Reverse any two-phase leads.
A step-up transformer.

33. 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?
200 volts AC.
150 turns.
Check to make sure that the victim is not still in contact with the electricity.
At the source transformer.

34. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Four times less than that of the secondary.
A.C.
No.6 AWG.
Stator windings.

35. Current transformers - or CT's - are used to...
H terminals.
The capacitors should be discharged.
5:1
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

36. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
A step-up transformer.
Nearly constant.
Disconnect the frame-grounding conductor.
Derive a neutral for grounding purposes.

37. The combined capacitance of two capacitors in parallel is...
H terminals.
Larger than that found in the primary winding.
The sum of the two capacitors.
An electromagnet.

38. The secondary windings on a 10:1 step-down transformer will have a wire size...
Kilovolt ampere (KVA).
7 -630 volts.
Full-load - three-phase voltage.
Larger than that found in the primary winding.

39. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
Four times less than that of the secondary.
3 -979 Volts.
Stator windings.

40. Compared to the secondary of a loaded - step-down transformer - the primary has...
480 volts.
150 turns.
Lower current and higher voltage.
A.C.

41. What steps up or steps down AC voltage?
They must be installed at least 7 feet above the ground.
Current that changes constantly in magnitude and periodically in direction.
Transformer
Reverse any two-phase leads.

42. AC voltage is raised or lowered by means of...
12 to 15 times a minute.
Squirrel-cage induction motor.
Transformers.
3 -979 Volts.

43. The property of an electrical circuit that opposes any change in voltage is called...
Kilovolt ampere (KVA).
No.6 AWG.
Electro-magnetism for their operation.
Capacitance.

44. 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.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
5:1.
They must be installed at least 7 feet above the ground.
Capacitance.

45. 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.
Electro-magnetism for their operation.
The capacitors should be discharged.
277 volts.

46. 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...
Inductance.
Draw less current.
480 volts.
Tied together

47. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
Second-degree burn.
A grounding resistor.
3 -979 Volts.

48. Current in an AC circuit may be measured by...
Because less current flowing at high voltage causes less line loss per kilowatt.
The current will read zero.
Clamp-on ammeter.
Disconnect the frame-grounding conductor.

49. What is the first step to be followed in aiding a victim of electrical shock?
Check to make sure that the victim is not still in contact with the electricity.
The motor rotation is reversed.
Alternating current.
Because less current flowing at high voltage causes less line loss per kilowatt.

50. Where should grounding resistors be located?
No.6 AWG.
At the source transformer.
3 -979 Volts.
150 turns.