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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. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
150 turns.
Stator windings.
Disconnect the frame-grounding conductor.
Zero amps.

2. At what rate should mouth-to-mouth resuscitation be applied?
Two speeds
12 to 15 times a minute.
Reverse its rotation.
Potential transformer.

3. All transformers step voltage up or down by...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Inductance.
Transformer
480 volts.

4. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
12 to 15 times a minute.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
1 amp.
Capacitance.

5. Current transformers - or CT's - are used to...
The current will read zero.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Lower current and higher voltage
No.6 AWG.

6. The main function of CT's and PT's on a main substation is to...
Cut around clothing that has adhered to the burned area.
Inductance.
277 volts.
Allow for metering voltage and Current.

7. What steps up or steps down AC voltage?
60 cycles per second (60 Hertz).
Transformer
Potential transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

8. The primary leads of a single-phase transformer should be connected to the...
Draw less current.
3 -979 Volts.
H terminals.
Current changing constantly in magnitude and periodically in direction.

9. 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?
The chest should rise or inflate.
Second-degree burn.
600 volts.
Clamp-on ammeter.

10. 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?
The current will read zero.
Second-degree burn.
Clamp-on ammeter.
800 volts.

11. 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?
100 turns.
Derive a neutral for grounding purposes.
1 amp.
Transformers.

12. What type motor is a wound-rotor induction motor?
277 volts.
A.C.
The motor rotation is reversed.
Nearly constant.

13. Not an acceptable method for the installations of surface transformers?
7 -630 volts.
They must be installed at least 7 feet above the ground.
15 feet off the ground.
100 turns.

14. The size of a transformer is measured in...
Kilovolt ampere (KVA).
The motor rotation is reversed.
Lower current and higher voltage
An electrical shock hazard may exist.

15. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
75 turns.
They must be installed at least 7 feet above the ground.
Clamp-on ammeter.
7 -630 volts.

16. What is the danger when working around capacitors?
600 volts.
An electrical shock hazard may exist.
Draw less current.
H terminals.

17. What is a capacitor?
A device used to store electrical energy.
Tied together
Reverse its rotation.
Transformer

18. A control power transformer...
Lower current and higher voltage.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Two speeds
No.6 AWG.

19. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
480 volts.
Nearly constant.
Isolation transformer.
The chest should rise or inflate.

20. The purpose of a zig-zag transformer is to...
25 feet.
Allow for metering voltage and Current.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Derive a neutral for grounding purposes.

21. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Potential transformer.
A.C.
A grounding resistor.
At least two phases

22. A solenoid coil is...
200 volts AC.
Check to make sure that the victim is not still in contact with the electricity.
An electromagnet.
Electro-magnetism for their operation.

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...
Squirrel-cage rotor.
277 volts.
Draw less current.
Current that changes constantly in magnitude and periodically in direction.

24. 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.
200 volts AC.
The sum of the two capacitors.
Full-load - three-phase voltage.

25. The secondary windings on a 10:1 step-down transformer will have a wire size...
Draw less current.
100 volts.
Squirrel-cage induction motor.
Larger than that found in the primary winding.

26. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
Circuit Breaker.
Isolation transformer.
Capacitance.

27. The most reliable method to use to determine whether or not the heart has stopped is by checking the...

28. 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?
60 cycles per second (60 Hertz).
Transformer
1 amp.
3 -979 Volts.

29. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
At least two phases
Grounded phase and ground fault devices were not operating.
X.
They should be made by the same manufacturer.

30. The standard frequency of alternating current used at a mine is...
60 Hertz
12 to 15 times a minute.
Lower current and higher voltage.
Alternating current.

31. Where should grounding resistors be located?
At the source transformer.
A step-up transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.
Derive a neutral for grounding purposes.

32. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
It provides good speed control.
150 turns.
75 turns.

33. The combined capacitance of two capacitors in parallel is...
Lower current and higher voltage
Inductance.
An electrical shock hazard may exist.
The sum of the two capacitors.

34. Three-phase AC underground cables must be provided with overcurrent protection using a...
No.6 AWG.
1 amp.
Inductance.
Circuit Breaker.

35. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
150 turns.
The sum of the two capacitors.
Inductance.

36. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
It provides good speed control.
Larger than that found in the primary winding.
Zero amps.
Second-degree burn.

37. Compared to the secondary of a loaded - step-down transformer - the primary has...
100 volts.
Continuous.
The motor rotation is reversed.
Lower current and higher voltage.

38. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
1 amp.
Nearly constant.
Two speeds
Potential transformer.

39. A burn causing a blister is classified as a...
5:1.
7 -630 volts.
Isolation transformer.
Second-degree burn.

40. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Draw less current.
The capacitors should be discharged.
Draw less current.
No.6 AWG.

41. Compared to the secondary of a loaded - step-down transformer - the primary has...
Shunted and taped
Lower current and higher voltage
Current that changes constantly in magnitude and periodically in direction.
X.

42. What should the duty rating of a grounding resistor be?
Kilovolt ampere (KVA).
Four times less than that of the secondary.
150 turns.
Continuous.

43. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Disconnect the frame-grounding conductor.
Short-circuited after power has been removed.
The sum of the two capacitors.

44. 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?
150 turns.
Derive a neutral for grounding purposes.
Larger than that found in the primary winding.
25 feet.

45. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A device used to store electrical energy.
Larger than that found in the primary winding.
A step-up transformer.
A.C.

46. 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.
Reverse its rotation.
Because less current flowing at high voltage causes less line loss per kilowatt.
5:1
Shunted and taped

47. 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.
Clamp-on ammeter.
Draw less current.
It provides good speed control.

48. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Carotid pulse - which is located in the neck next to the Adam's apple.
2000 watts
Larger than that found in the primary winding.
800 volts.

49. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
277 volts.
3 -979 Volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
Four times less than that of the secondary.

50. 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.
An electrical shock hazard may exist.
Kilovolt ampere (KVA).
2000 watts