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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. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
Full-load - three-phase voltage.
15 feet off the ground.
A step-up transformer.

2. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Disconnect the frame-grounding conductor.
Zero amps.
Because less current flowing at high voltage causes less line loss per kilowatt.
2000 watts

3. What steps up or steps down AC voltage?
Transformer
Reverse its rotation.
Disconnect the frame-grounding conductor.
5:1

4. Alternating current may be defined as...
Zero amps.
Current that changes constantly in magnitude and periodically in direction.
Because less current flowing at high voltage causes less line loss per kilowatt.
Disconnect the frame-grounding conductor.

5. The transformer used only to measure voltage is a...
Second-degree burn.
Potential transformer.
Inductance.
H terminals.

6. 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?
Inductance.
3 -979 Volts.
1 amp.
Stator windings.

7. 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?
Electro-magnetism for their operation.
Because less current flowing at high voltage causes less line loss per kilowatt.
200 volts AC.
Current that changes constantly in magnitude and periodically in direction.

8. The standard frequency of alternating current used at a mine is...
Current changing constantly in magnitude and periodically in direction.
Lower current and higher voltage.
60 Hertz
Because less current flowing at high voltage causes less line loss per kilowatt.

9. Compared to the secondary of a loaded - step-down transformer - the primary has...
Inductance.
Clamp-on ammeter.
Draw less current.
Lower current and higher voltage.

10. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The capacitors should be discharged.
The current will read zero.
They must be installed at least 7 feet above the ground.
Clamp-on ammeter.

11. Three-phase AC underground cables must be provided with overcurrent protection using a...
At least two phases
An electrical shock hazard may exist.
2000 watts
Circuit Breaker.

12. A transformer with a 1:1 ratio is usually a (an)...
Draw less current.
Isolation transformer.
Two speeds
X.

13. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
1 amp.
A device used to store electrical energy.
7 -630 volts.
The sum of the two capacitors.

14. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Transformer
A.C.
Current changing constantly in magnitude and periodically in direction.
480 volts.

15. Current in an AC circuit may be measured by...
480 volts.
Clamp-on ammeter.
75 turns.
The capacitors should be discharged.

16. All transformers step voltage up or down by...
Second-degree burn.
3 -979 Volts.
Inductance.
Kilovolt ampere (KVA).

17. Current that changes periodically in direction is...
3 -979 Volts.
Reverse its rotation.
Second-degree burn.
Alternating current.

18. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The sum of the two capacitors.
Current that changes constantly in magnitude and periodically in direction.
100 turns.

19. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Tied together
Nearly constant.
Disconnect the frame-grounding conductor.
Continuous.

20. 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.
Current that changes constantly in magnitude and periodically in direction.
Two speeds
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

21. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
Tied together
Stator windings.
Squirrel-cage induction motor.

22. When not connected to a load - the secondary leads of a current transformer should be...
The sum of the two capacitors.
Zero amps.
Shunted and taped
Because less current flowing at high voltage causes less line loss per kilowatt.

23. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Full-load - three-phase voltage.
Lower current and higher voltage.
Isolation transformer.
25 feet.

24. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
100 turns.
No.6 AWG.
X.

25. 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.
Because less current flowing at high voltage causes less line loss per kilowatt.
Clamp-on ammeter.
A step-up transformer.

26. High voltage is used to transmit power over long distances...
A grounding resistor.
Squirrel-cage induction motor.
Shunted and taped
Because less current flowing at high voltage causes less line loss per kilowatt.

27. The property of an electric circuit that opposes any change in current is called...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Carotid pulse - which is located in the neck next to the Adam's apple.
Inductance.
Short-circuited after power has been removed.

28. What is a capacitor?
Allow for metering voltage and Current.
A device used to store electrical energy.
7 -630 volts.
Cut around clothing that has adhered to the burned area.

29. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Circuit Breaker.
X.
60 Hertz
Reverse any two-phase leads.

30. 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...
Hyperventilation.
15 feet off the ground.
75 turns.
Tied together

31. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Second-degree burn.
No.6 AWG.
3 -979 Volts.
Transformers.

32. What is the first step to be followed in aiding a victim of electrical shock?
Clamp-on ammeter.
Check to make sure that the victim is not still in contact with the electricity.
480 volts.
12 to 15 times a minute.

33. At what rate should mouth-to-mouth resuscitation be applied?
A device used to store electrical energy.
12 to 15 times a minute.
60 cycles per second (60 Hertz).
150 turns.

34. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
Tied together
Disconnect the frame-grounding conductor.
5:1

35. The property of an electrical circuit that opposes any change in voltage is called...
Clamp-on ammeter.
Capacitance.
At the source transformer.
It provides good speed control.

36. Where should grounding resistors be located?
Current changing constantly in magnitude and periodically in direction.
At the source transformer.
Circuit Breaker.
Zero amps.

37. 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.
Continuous.
X.
25 feet.

38. 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?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
800 volts.
Stator windings.
Squirrel-cage induction motor.

39. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
H terminals.
15 feet off the ground.
Tied together
Potential transformer.

40. 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.
200 volts AC.
Cut around clothing that has adhered to the burned area.
100 volts.

41. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
At the source transformer.
Allow for metering voltage and Current.
12 to 15 times a minute.
They should be made by the same manufacturer.

42. A burn causing a blister is classified as a...
5:1.
An electrical shock hazard may exist.
X.
Second-degree burn.

43. Which of the following does a squirrel cage induction motor have?
Second-degree burn.
1 amp.
Stator windings.
75 turns.

44. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Draw less current.
Hyperventilation.
75 turns.

45. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
An electrical shock hazard may exist.
Short-circuited after power has been removed.
The capacitors should be discharged.
600 volts.

46. What is the danger when working around capacitors?
Transformers.
A step-up transformer.
Nearly constant.
An electrical shock hazard may exist.

47. Not a symptom of electrical shock?.
200 volts AC.
Clamp-on ammeter.
Hyperventilation.
The capacitors should be discharged.

48. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
3 -979 Volts.
Reverse its rotation.
Nearly constant.

49. A control power transformer...
75 turns.
Provides single-phase power to smaller loads such as lights - heaters - etc.
100 turns.
Check to make sure that the victim is not still in contact with the electricity.

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.
The capacitors should be discharged.
Reverse any two-phase leads.
75 turns.