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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. What is the first step to be followed in aiding a victim of electrical shock?
Derive a neutral for grounding purposes.
Stator windings.
Check to make sure that the victim is not still in contact with the electricity.
An electromagnet.

2. How should clothing be removed from a burn?
Reverse any two-phase leads.
480 volts.
Cut around clothing that has adhered to the burned area.
Grounded phase and ground fault devices were not operating.

3. What should the duty rating of a grounding resistor be?
Continuous.
The chest should rise or inflate.
Current changing constantly in magnitude and periodically in direction.
7 -630 volts.

4. The primary leads of a single-phase transformer should be connected to the...
3 -979 Volts.
No.6 AWG.
H terminals.
Hyperventilation.

5. A wound-rotor induction motor has all the following EXCEPT...
Grounded phase and ground fault devices were not operating.
Squirrel-cage rotor.
25 feet.
The motor rotation is reversed.

6. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The chest should rise or inflate.
Second-degree burn.
25 feet.

7. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
Squirrel-cage induction motor.
Lower current and higher voltage.
Circuit Breaker.

8. The standard frequency of alternating current used at a mine is...
Because less current flowing at high voltage causes less line loss per kilowatt.
60 Hertz
480 volts.
Clamp-on ammeter.

9. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
1 amp.
X.
A.C.
Transformer

10. A solenoid coil is...
The motor rotation is reversed.
Disconnect the frame-grounding conductor.
An electromagnet.
Isolation transformer.

11. At what rate should mouth-to-mouth resuscitation be applied?
Allow for metering voltage and Current.
12 to 15 times a minute.
Kilovolt ampere (KVA).
75 turns.

12. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
A device used to store electrical energy.
200 volts AC.
X.
Two speeds

13. Define alternating current...
The chest should rise or inflate.
Current changing constantly in magnitude and periodically in direction.
75 turns.
Check to make sure that the victim is not still in contact with the electricity.

14. The property of an electrical circuit that opposes any change in voltage is called...
Reverse any two-phase leads.
Clamp-on ammeter.
Allow for metering voltage and Current.
Capacitance.

15. The speed of an alternating current - squirrel-cage induction motor is...
12 to 15 times a minute.
Draw less current.
Nearly constant.
It provides good speed control.

16. 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...
15 feet off the ground.
The sum of the two capacitors.
Draw less current.
Zero amps.

17. How do you change the direction of a 3-phase AC motor?
The motor rotation is reversed.
Reverse any two-phase leads.
A.C.
Full-load - three-phase voltage.

18. 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.
100 volts.
X.
Current changing constantly in magnitude and periodically in direction.
5:1

19. 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?
Alternating current.
Cut around clothing that has adhered to the burned area.
75 turns.
Transformers.

20. 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...
Current that changes constantly in magnitude and periodically in direction.
1 amp.
100 volts.
An electrical shock hazard may exist.

21. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
100 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Capacitance.

22. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
A grounding resistor.
Lower current and higher voltage
100 volts.

23. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
800 volts.
Current changing constantly in magnitude and periodically in direction.
Kilovolt ampere (KVA).

24. Current that changes periodically in direction is...
Draw less current.
Alternating current.
The current will read zero.
Capacitance.

25. Current transformers - or CT's - are used to...
At the source transformer.
Kilovolt ampere (KVA).
A grounding resistor.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

26. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
An electrical shock hazard may exist.
Clamp-on ammeter.
3 -979 Volts.

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?
The sum of the two capacitors.
Zero amps.
Current that changes constantly in magnitude and periodically in direction.
200 volts AC.

28. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
It provides good speed control.
They should be made by the same manufacturer.
Four times less than that of the secondary.
Disconnect the frame-grounding conductor.

29. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Check to make sure that the victim is not still in contact with the electricity.
The current will read zero.
Full-load - three-phase voltage.

30. 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.
Transformers.
Draw less current.
Transformer

31. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Check to make sure that the victim is not still in contact with the electricity.
At the source transformer.
15 feet off the ground.

32. 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...
An electromagnet.
Stator windings.
Draw less current.
Lower current and higher voltage.

33. A burn causing a blister is classified as a...
Second-degree burn.
A grounding resistor.
Check to make sure that the victim is not still in contact with the electricity.
They must be installed at least 7 feet above the ground.

34. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
A device used to store electrical energy.
2000 watts
Inductance.
Shunted and taped

35. Not a symptom of electrical shock?.
75 turns.
Hyperventilation.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
At the source transformer.

36. 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...
Tied together
H terminals.
They must be installed at least 7 feet above the ground.
15 feet off the ground.

37. The secondary windings on a 10:1 step-down transformer will have a wire size...
1 amp.
75 turns.
The capacitors should be discharged.
Larger than that found in the primary winding.

38. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
X.
100 volts.
They should be made by the same manufacturer.
200 volts AC.

39. Not an acceptable method for the installations of surface transformers?
Draw less current.
H terminals.
Nearly constant.
They must be installed at least 7 feet above the ground.

40. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Zero amps.
It provides good speed control.
The motor rotation is reversed.
Isolation transformer.

41. The size of a transformer is measured in...
Kilovolt ampere (KVA).
The current will read zero.
600 volts.
Draw less current.

42. 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?
Reverse its rotation.
12 to 15 times a minute.
3 -979 Volts.
A grounding resistor.

43. The transformer used only to measure voltage is a...
5:1
600 volts.
Potential transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

44. The combined capacitance of two capacitors in parallel is...
Hyperventilation.
Cut around clothing that has adhered to the burned area.
The sum of the two capacitors.
A device used to store electrical energy.

45. Not true about AC power?
At least two phases
It provides good speed control.
600 volts.
Draw less current.

46. Compared to the secondary of a loaded - step-down transformer - the primary has...
The current will read zero.
150 turns.
H terminals.
Lower current and higher voltage.

47. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Short-circuited after power has been removed.
277 volts.
Check to make sure that the victim is not still in contact with the electricity.
25 feet.

48. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Squirrel-cage rotor.
Draw less current.
1 amp.
Hyperventilation.

49. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
The current will read zero.
15 feet off the ground.
Grounded phase and ground fault devices were not operating.
Hyperventilation.

50. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
X.
The capacitors should be discharged.
100 turns.
The current will read zero.