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 with a 1:1 ratio is usually a (an)...
Isolation transformer.
Kilovolt ampere (KVA).
Draw less current.
Shunted and taped

2. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Carotid pulse - which is located in the neck next to the Adam's apple.
480 volts.
Lower current and higher voltage.
Because less current flowing at high voltage causes less line loss per kilowatt.

3. Not an acceptable method for the installations of surface transformers?
3 -979 Volts.
They must be installed at least 7 feet above the ground.
An electrical shock hazard may exist.
Reverse its rotation.

4. The standard frequency of alternating current used at a mine is...
Squirrel-cage induction motor.
60 Hertz
Capacitance.
Isolation transformer.

5. The transformer used only to measure voltage is a...
At the source transformer.
100 volts.
Potential transformer.
An electromagnet.

6. The property of an electric circuit that opposes any change in current is called...
Inductance.
200 volts AC.
Shunted and taped
Four times less than that of the secondary.

7. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Full-load - three-phase voltage.
No.6 AWG.
277 volts.
The capacitors should be discharged.

8. Not a symptom of electrical shock?.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Hyperventilation.
Draw less current.
Reverse any two-phase leads.

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...
Larger than that found in the primary winding.
Second-degree burn.
100 volts.
Kilovolt ampere (KVA).

10. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
Second-degree burn.
Alternating current.
100 turns.

11. How do you change the direction of a 3-phase AC motor?
60 cycles per second (60 Hertz).
100 turns.
Reverse any two-phase leads.
X.

12. How should clothing be removed from a burn?
Transformer
Lower current and higher voltage.
Cut around clothing that has adhered to the burned area.
60 Hertz

13. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
150 turns.
A step-up transformer.
60 Hertz

14. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Circuit Breaker.
Stator windings.
Electro-magnetism for their operation.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

15. Current transformers - or CT's - are used to...
5:1.
Inductance.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Tied together

16. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Current changing constantly in magnitude and periodically in direction.
Inductance.
Full-load - three-phase voltage.
Four times less than that of the secondary.

17. 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...
75 turns.
600 volts.
Tied together
75 turns.

18. 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.
12 to 15 times a minute.
Check to make sure that the victim is not still in contact with the electricity.
Draw less current.

19. The combined capacitance of two capacitors in parallel is...
Inductance.
The sum of the two capacitors.
Current changing constantly in magnitude and periodically in direction.
200 volts AC.

20. 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.
Two speeds
Disconnect the frame-grounding conductor.
Zero amps.

21. What is a capacitor?
Carotid pulse - which is located in the neck next to the Adam's apple.
60 Hertz
A device used to store electrical energy.
A.C.

22. What steps up or steps down AC voltage?
Check to make sure that the victim is not still in contact with the electricity.
480 volts.
277 volts.
Transformer

23. Define alternating current...
1 amp.
Current changing constantly in magnitude and periodically in direction.
100 turns.
Allow for metering voltage and Current.

24. What is the first step to be followed in aiding a victim of electrical shock?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Check to make sure that the victim is not still in contact with the electricity.
Short-circuited after power has been removed.
Continuous.

25. Current in an AC circuit may be measured by...
Shunted and taped
Draw less current.
Tied together
Clamp-on ammeter.

26. The speed of an alternating current - squirrel-cage induction motor is...
Lower current and higher voltage.
800 volts.
Hyperventilation.
Nearly constant.

27. If any two-phase wires are reversed on a three-phase motor - the motor will...
Zero amps.
They must be installed at least 7 feet above the ground.
Reverse its rotation.
2000 watts

28. The main function of CT's and PT's on a main substation is to...
5:1.
No.6 AWG.
Disconnect the frame-grounding conductor.
Allow for metering voltage and Current.

29. 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?
Kilovolt ampere (KVA).
60 cycles per second (60 Hertz).
600 volts.
Reverse any two-phase leads.

30. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
25 feet.
They should be made by the same manufacturer.
Isolation transformer.
Circuit Breaker.

31. 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?
Derive a neutral for grounding purposes.
75 turns.
800 volts.
An electrical shock hazard may exist.

32. 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.
Cut around clothing that has adhered to the burned area.
Continuous.
Nearly constant.

33. What type motor is a wound-rotor induction motor?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
A.C.
Nearly constant.
A grounding resistor.

34. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The current will read zero.
Hyperventilation.
Lower current and higher voltage
Because less current flowing at high voltage causes less line loss per kilowatt.

35. The primary leads of a single-phase transformer should be connected to the...
Reverse its rotation.
H terminals.
Allow for metering voltage and Current.
Reverse any two-phase leads.

36. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
Allow for metering voltage and Current.
150 turns.
No.6 AWG.

37. Three-phase AC underground cables must be provided with overcurrent protection using a...
Grounded phase and ground fault devices were not operating.
Electro-magnetism for their operation.
5:1.
Circuit Breaker.

38. The property of an electrical circuit that opposes any change in voltage is called...
277 volts.
Squirrel-cage rotor.
Capacitance.
Check to make sure that the victim is not still in contact with the electricity.

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

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

41. 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 sum of the two capacitors.
100 turns.
480 volts.
200 volts AC.

42. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
2000 watts
7 -630 volts.
Tied together

43. High voltage is used to transmit power over long distances...
Capacitance.
Transformer
150 turns.
Because less current flowing at high voltage causes less line loss per kilowatt.

44. All transformers step voltage up or down by...
Reverse any two-phase leads.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
75 turns.
Inductance.

45. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
100 volts.
Disconnect the frame-grounding conductor.
480 volts.
A step-up transformer.

46. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Reverse any two-phase leads.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Two speeds
A grounding resistor.

47. Compared to the secondary of a loaded - step-down transformer - the primary has...
100 volts.
Draw less current.
The sum of the two capacitors.
Lower current and higher voltage

48. The standard frequency of power supplied by the power company is...
25 feet.
100 volts.
Transformer
60 cycles per second (60 Hertz).

49. 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?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
75 turns.
The chest should rise or inflate.
The sum of the two capacitors.

50. To protect against over-current in a three-phase circuit over-current protection must be provided for...
An electromagnet.
At least two phases
Short-circuited after power has been removed.
75 turns.