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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. High voltage is used to transmit power over long distances...
5:1
Kilovolt ampere (KVA).
Because less current flowing at high voltage causes less line loss per kilowatt.
Tied together

2. When not connected to a load - the secondary leads of a current transformer should be...
Kilovolt ampere (KVA).
A device used to store electrical energy.
Shunted and taped
Squirrel-cage induction motor.

3. Compared to the secondary of a loaded - step-down transformer - the primary has...
X.
75 turns.
150 turns.
Lower current and higher voltage

4. 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.
5:1
Check to make sure that the victim is not still in contact with the electricity.
Clamp-on ammeter.

5. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
480 volts.
Reverse its rotation.
The motor rotation is reversed.
15 feet off the ground.

6. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Zero amps.
75 turns.
X.
7 -630 volts.

7. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Circuit Breaker.
Squirrel-cage rotor.
5:1.

8. 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?
800 volts.
Allow for metering voltage and Current.
Nearly constant.
Current changing constantly in magnitude and periodically in direction.

9. Not a symptom of electrical shock?.
Grounded phase and ground fault devices were not operating.
Carotid pulse - which is located in the neck next to the Adam's apple.
Hyperventilation.
3 -979 Volts.

10. What is the danger when working around capacitors?
Short-circuited after power has been removed.
2000 watts
An electrical shock hazard may exist.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

11. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
Isolation transformer.
A grounding resistor.
The current will read zero.

12. 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.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The capacitors should be discharged.
5:1
Carotid pulse - which is located in the neck next to the Adam's apple.

13. What type motor is a wound-rotor induction motor?
Clamp-on ammeter.
A.C.
800 volts.
Zero amps.

14. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Kilovolt ampere (KVA).
They should be made by the same manufacturer.
Squirrel-cage rotor.
Zero amps.

15. 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?
H terminals.
Because less current flowing at high voltage causes less line loss per kilowatt.
150 turns.
5:1.

16. The property of an electric circuit that opposes any change in current is called...
A device used to store electrical energy.
Because less current flowing at high voltage causes less line loss per kilowatt.
5:1.
Inductance.

17. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The chest should rise or inflate.
Inductance.
The capacitors should be discharged.
Circuit Breaker.

18. The transformer used only to measure voltage is a...
An electromagnet.
Cut around clothing that has adhered to the burned area.
Lower current and higher voltage
Potential transformer.

19. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Kilovolt ampere (KVA).
277 volts.
An electromagnet.
Capacitance.

20. Not an acceptable method for the installations of surface transformers?
An electromagnet.
Larger than that found in the primary winding.
1 amp.
They must be installed at least 7 feet above the ground.

21. Current in an AC circuit may be measured by...
Clamp-on ammeter.
A device used to store electrical energy.
Carotid pulse - which is located in the neck next to the Adam's apple.
Grounded phase and ground fault devices were not operating.

22. The primary function of a power transformer is to provide...
12 to 15 times a minute.
Squirrel-cage induction motor.
Full-load - three-phase voltage.
At least two phases

23. 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...
An electromagnet.
Four times less than that of the secondary.
At the source transformer.
Draw less current.

24. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
277 volts.
Potential transformer.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

25. 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?
12 to 15 times a minute.
Because less current flowing at high voltage causes less line loss per kilowatt.
75 turns.
100 turns.

26. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Capacitance.
Four times less than that of the secondary.
An electromagnet.
12 to 15 times a minute.

27. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Reverse its rotation.
75 turns.
A grounding resistor.
Check to make sure that the victim is not still in contact with the electricity.

28. The standard frequency of alternating current used at a mine is...
60 Hertz
The capacitors should be discharged.
1 amp.
15 feet off the ground.

29. 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.
A step-up transformer.
480 volts.
Lower current and higher voltage

30. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
They should be made by the same manufacturer.
15 feet off the ground.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Circuit Breaker.

31. Three-phase AC underground cables must be provided with overcurrent protection using a...
Because less current flowing at high voltage causes less line loss per kilowatt.
Circuit Breaker.
3 -979 Volts.
Electro-magnetism for their operation.

32. How do you change the direction of a 3-phase AC motor?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
200 volts AC.
60 Hertz
Reverse any two-phase leads.

33. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
5:1
60 Hertz
Lower current and higher voltage

34. 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?
277 volts.
The current will read zero.
75 turns.
An electrical shock hazard may exist.

35. 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...
800 volts.
Draw less current.
Electro-magnetism for their operation.
Capacitance.

36. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Draw less current.
No.6 AWG.
Reverse any two-phase leads.
Alternating current.

37. The purpose of a zig-zag transformer is to...
1 amp.
They must be installed at least 7 feet above the ground.
100 volts.
Derive a neutral for grounding purposes.

38. AC voltage is raised or lowered by means of...
Transformers.
The chest should rise or inflate.
3 -979 Volts.
A step-up transformer.

39. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Larger than that found in the primary winding.
Inductance.
Draw less current.
At least two phases

40. What steps up or steps down AC voltage?
Reverse its rotation.
X.
Transformer
75 turns.

41. 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
Tied together
An electromagnet.
Potential transformer.

42. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Short-circuited after power has been removed.
An electromagnet.
Reverse any two-phase leads.
Draw less current.

43. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Reverse any two-phase leads.
480 volts.
Electro-magnetism for their operation.

44. The main function of CT's and PT's on a main substation is to...
Zero amps.
The capacitors should be discharged.
Allow for metering voltage and Current.
H terminals.

45. The property of an electrical circuit that opposes any change in voltage is called...
Shunted and taped
Inductance.
Four times less than that of the secondary.
Capacitance.

46. Not true about AC power?
At least two phases
Draw less current.
It provides good speed control.
60 cycles per second (60 Hertz).

47. 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.
5:1.
Full-load - three-phase voltage.
A step-up transformer.
The current will read zero.

48. The size of a transformer is measured in...
7 -630 volts.
Cut around clothing that has adhered to the burned area.
They must be installed at least 7 feet above the ground.
Kilovolt ampere (KVA).

49. Current transformers - or CT's - are used to...
Check to make sure that the victim is not still in contact with the electricity.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
75 turns.
A step-up transformer.

50. 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?
Draw less current.
Hyperventilation.
277 volts.
75 turns.