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Test your basic knowledge |

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 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?
An electrical shock hazard may exist.
The motor rotation is reversed.
75 turns.
They must be installed at least 7 feet above the ground.

2. What type motor is a wound-rotor induction motor?
An electromagnet.
A.C.
Derive a neutral for grounding purposes.
800 volts.

3. The primary function of a power transformer is to provide...
A.C.
Current changing constantly in magnitude and periodically in direction.
Transformer
Full-load - three-phase voltage.

4. 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.
At the source transformer.
5:1
2000 watts
No.6 AWG.

5. What is the danger when working around capacitors?
An electrical shock hazard may exist.
12 to 15 times a minute.
150 turns.
277 volts.

6. What should the duty rating of a grounding resistor be?
Kilovolt ampere (KVA).
Carotid pulse - which is located in the neck next to the Adam's apple.
Continuous.
Second-degree burn.

7. 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?
Grounded phase and ground fault devices were not operating.
150 turns.
7 -630 volts.
A device used to store electrical energy.

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.
Derive a neutral for grounding purposes.
100 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.

9. 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
Isolation transformer.
Squirrel-cage induction motor.
5:1

10. The transformer used only to measure voltage is a...
800 volts.
Potential transformer.
100 volts.
600 volts.

11. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Second-degree burn.
Inductance.
X.
Lower current and higher voltage

12. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
Because less current flowing at high voltage causes less line loss per kilowatt.
Continuous.
60 cycles per second (60 Hertz).

13. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
5:1
Inductance.
Zero amps.
Cut around clothing that has adhered to the burned area.

14. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
60 cycles per second (60 Hertz).
A.C.
No.6 AWG.

15. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Current that changes constantly in magnitude and periodically in direction.
600 volts.
At least two phases
The current will read zero.

16. Current that changes periodically in direction is...
Allow for metering voltage and Current.
Alternating current.
The capacitors should be discharged.
H terminals.

17. The primary leads of a single-phase transformer should be connected to the...
150 turns.
75 turns.
The capacitors should be discharged.
H terminals.

18. Alternating current may be defined as...
Carotid pulse - which is located in the neck next to the Adam's apple.
At the source transformer.
Zero amps.
Current that changes constantly in magnitude and periodically in direction.

19. When not connected to a load - the secondary leads of a current transformer should be...
No.6 AWG.
Capacitance.
Larger than that found in the primary winding.
Shunted and taped

20. Compared to the secondary of a loaded - step-down transformer - the primary has...
No.6 AWG.
60 Hertz
Lower current and higher voltage
Zero amps.

21. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Capacitance.
A grounding resistor.
At least two phases
It provides good speed control.

22. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
100 volts.
60 cycles per second (60 Hertz).
No.6 AWG.

23. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Disconnect the frame-grounding conductor.
Two speeds
Four times less than that of the secondary.
Reverse any two-phase leads.

24. Not true about AC power?
Isolation transformer.
The chest should rise or inflate.
It provides good speed control.
2000 watts

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

26. What is a capacitor?
2000 watts
Shunted and taped
A device used to store electrical energy.
They should be made by the same manufacturer.

27. 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?
A step-up transformer.
25 feet.
200 volts AC.
The sum of the two capacitors.

28. 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...
Isolation transformer.
1 amp.
They should be made by the same manufacturer.
Draw less current.

29. The standard frequency of alternating current used at a mine is...
Hyperventilation.
At least two phases
60 Hertz
2000 watts

30. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Tied together
They must be installed at least 7 feet above the ground.
An electromagnet.
Four times less than that of the secondary.

31. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Isolation transformer.
A device used to store electrical energy.
7 -630 volts.
Draw less current.

32. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
Current that changes constantly in magnitude and periodically in direction.
An electrical shock hazard may exist.
Full-load - three-phase voltage.

33. 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.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Tied together
Reverse any two-phase leads.

34. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
Current changing constantly in magnitude and periodically in direction.
277 volts.
It provides good speed control.

35. 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.
Allow for metering voltage and Current.
12 to 15 times a minute.
The current will read zero.

36. 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?
Short-circuited after power has been removed.
Electro-magnetism for their operation.
An electrical shock hazard may exist.
75 turns.

37. 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...
H terminals.
100 volts.
600 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

38. A burn causing a blister is classified as a...
60 Hertz
Second-degree burn.
100 turns.
12 to 15 times a minute.

39. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
Cut around clothing that has adhered to the burned area.
Circuit Breaker.
Full-load - three-phase voltage.

40. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
75 turns.
60 Hertz
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
No.6 AWG.

41. Not an acceptable method for the installations of surface transformers?
7 -630 volts.
277 volts.
Alternating current.
They must be installed at least 7 feet above the ground.

42. The size of a transformer is measured in...
Isolation transformer.
Kilovolt ampere (KVA).
Capacitance.
Carotid pulse - which is located in the neck next to the Adam's apple.

43. All transformers step voltage up or down by...
Inductance.
Transformer
Two speeds
Short-circuited after power has been removed.

44. 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?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
3 -979 Volts.
Check to make sure that the victim is not still in contact with the electricity.
150 turns.

45. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
A grounding resistor.
Because less current flowing at high voltage causes less line loss per kilowatt.
480 volts.
The current will read zero.

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...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Because less current flowing at high voltage causes less line loss per kilowatt.
Hyperventilation.
Tied together

47. A solenoid coil is...
An electromagnet.
Tied together
75 turns.
Shunted and taped

48. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
277 volts.
Alternating current.
100 turns.

49. 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?
75 turns.
Because less current flowing at high voltage causes less line loss per kilowatt.
Squirrel-cage rotor.
100 turns.

50. The property of an electrical circuit that opposes any change in voltage is called...
The motor rotation is reversed.
Second-degree burn.
Hyperventilation.
Capacitance.