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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 position of a selector switch using a voltmeter would you select to check a 120-volt AC circuit to obtain the most accurate reading?
150 turns.
200 volts AC.
Lower current and higher voltage.
100 turns.

2. A control power transformer...
Inductance.
Provides single-phase power to smaller loads such as lights - heaters - etc.
The capacitors should be discharged.
A step-up transformer.

3. Alternating current may be defined as...
Reverse any two-phase leads.
An electrical shock hazard may exist.
Current that changes constantly in magnitude and periodically in direction.
Nearly constant.

4. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
150 turns.
No.6 AWG.
75 turns.
Tied together

5. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Check to make sure that the victim is not still in contact with the electricity.
Potential transformer.
Transformer

6. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
75 turns.
75 turns.
Squirrel-cage rotor.

7. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
480 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
At least two phases
Disconnect the frame-grounding conductor.

8. 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.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Tied together
Alternating current.
5:1

9. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
Transformers.
75 turns.
The capacitors should be discharged.

10. The speed of an alternating current - squirrel-cage induction motor is...
Inductance.
1 amp.
They must be installed at least 7 feet above the ground.
Nearly constant.

11. The primary function of a power transformer is to provide...
1 amp.
The chest should rise or inflate.
Cut around clothing that has adhered to the burned area.
Full-load - three-phase voltage.

12. 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?
Reverse any two-phase leads.
75 turns.
Cut around clothing that has adhered to the burned area.
Draw less current.

13. A solenoid coil is...
Cut around clothing that has adhered to the burned area.
An electromagnet.
2000 watts
600 volts.

14. Not true about AC power?
Squirrel-cage rotor.
It provides good speed control.
Second-degree burn.
Inductance.

15. The transformer used only to measure voltage is a...
Potential transformer.
Squirrel-cage induction motor.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
H terminals.

16. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
They should be made by the same manufacturer.
Nearly constant.
277 volts.
Squirrel-cage induction motor.

17. The standard frequency of power supplied by the power company is...
Continuous.
7 -630 volts.
60 cycles per second (60 Hertz).
Capacitance.

18. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Check to make sure that the victim is not still in contact with the electricity.
7 -630 volts.
Electro-magnetism for their operation.
No.6 AWG.

19. If any two-phase wires are reversed on a three-phase motor - the motor will...
277 volts.
Current that changes constantly in magnitude and periodically in direction.
Short-circuited after power has been removed.
Reverse its rotation.

20. The property of an electrical circuit that opposes any change in voltage is called...
Transformers.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Second-degree burn.
Capacitance.

21. Operating coils - motors - transformers - relays and solenoids depend upon...
A step-up transformer.
800 volts.
Current changing constantly in magnitude and periodically in direction.
Electro-magnetism for their operation.

22. Current transformers - or CT's - are used to...
Tied together
Hyperventilation.
Transformer
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

23. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Four times less than that of the secondary.
25 feet.
Clamp-on ammeter.
Short-circuited after power has been removed.

24. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
At the source transformer.
Capacitance.
7 -630 volts.

25. A wound-rotor induction motor has all the following EXCEPT...
The capacitors should be discharged.
Squirrel-cage rotor.
Capacitance.
The current will read zero.

26. The combined capacitance of two capacitors in parallel is...
200 volts AC.
Transformer
The sum of the two capacitors.
Cut around clothing that has adhered to the burned area.

27. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Nearly constant.
Capacitance.
X.
Draw less current.

28. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Allow for metering voltage and Current.
An electrical shock hazard may exist.
Grounded phase and ground fault devices were not operating.
Draw less current.

29. 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.
60 Hertz
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Current changing constantly in magnitude and periodically in direction.

30. At what rate should mouth-to-mouth resuscitation be applied?
Four times less than that of the secondary.
12 to 15 times a minute.
Transformer
200 volts AC.

31. How should clothing be removed from a burn?
Kilovolt ampere (KVA).
The chest should rise or inflate.
Cut around clothing that has adhered to the burned area.
An electrical shock hazard may exist.

32. Which of the following does a squirrel cage induction motor have?
Stator windings.
75 turns.
A step-up transformer.
600 volts.

33. What type motor is a wound-rotor induction motor?
Reverse its rotation.
Short-circuited after power has been removed.
Reverse any two-phase leads.
A.C.

34. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Squirrel-cage rotor.
480 volts.
Draw less current.
The current will read zero.

35. When not connected to a load - the secondary leads of a current transformer should be...
Reverse any two-phase leads.
They should be made by the same manufacturer.
Short-circuited after power has been removed.
Shunted and taped

36. A burn causing a blister is classified as a...
Capacitance.
Full-load - three-phase voltage.
Reverse its rotation.
Second-degree burn.

37. How do you change the direction of a 3-phase AC motor?
100 turns.
Reverse any two-phase leads.
H terminals.
25 feet.

38. Not a symptom of electrical shock?.
The motor rotation is reversed.
They must be installed at least 7 feet above the ground.
At the source transformer.
Hyperventilation.

39. 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...
The sum of the two capacitors.
Transformers.
X.
Tied together

40. Not an acceptable method for the installations of surface transformers?
The current will read zero.
They must be installed at least 7 feet above the ground.
A.C.
480 volts.

41. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
3 -979 Volts.
Nearly constant.
Inductance.

42. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
H terminals.
75 turns.
Kilovolt ampere (KVA).

43. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
At the source transformer.
600 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

44. 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?
Circuit Breaker.
Reverse its rotation.
480 volts.
75 turns.

45. The standard frequency of alternating current used at a mine is...
Inductance.
60 Hertz
100 volts.
5:1.

46. Compared to the secondary of a loaded - step-down transformer - the primary has...
They should be made by the same manufacturer.
Stator windings.
Potential transformer.
Lower current and higher voltage

47. 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...
Potential transformer.
A device used to store electrical energy.
Draw less current.
60 cycles per second (60 Hertz).

48. 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...
12 to 15 times a minute.
25 feet.
Draw less current.
Larger than that found in the primary winding.

49. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Because less current flowing at high voltage causes less line loss per kilowatt.
Nearly constant.
Current that changes constantly in magnitude and periodically in direction.
277 volts.

50. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Lower current and higher voltage
A grounding resistor.
No.6 AWG.