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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 main function of CT's and PT's on a main substation is to...
25 feet.
At the source transformer.
Allow for metering voltage and Current.
A device used to store electrical energy.

2. A solenoid coil is...
An electromagnet.
Lower current and higher voltage
H terminals.
Tied together

3. 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?
At the source transformer.
Second-degree burn.
Four times less than that of the secondary.
3 -979 Volts.

4. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
150 turns.
No.6 AWG.
200 volts AC.
Reverse its rotation.

5. Compared to the secondary of a loaded - step-down transformer - the primary has...
Carotid pulse - which is located in the neck next to the Adam's apple.
Inductance.
Lower current and higher voltage
5:1.

6. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Grounded phase and ground fault devices were not operating.
Disconnect the frame-grounding conductor.
Lower current and higher voltage.
Full-load - three-phase voltage.

7. Not a symptom of electrical shock?.
Hyperventilation.
Draw less current.
They should be made by the same manufacturer.
5:1

8. The primary leads of a single-phase transformer should be connected to the...
Alternating current.
H terminals.
A step-up transformer.
Reverse any two-phase leads.

9. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Nearly constant.
Reverse any two-phase leads.
The chest should rise or inflate.
5:1

10. What is the first step to be followed in aiding a victim of electrical shock?
Kilovolt ampere (KVA).
60 Hertz
200 volts AC.
Check to make sure that the victim is not still in contact with the electricity.

11. At what rate should mouth-to-mouth resuscitation be applied?
A grounding resistor.
12 to 15 times a minute.
Four times less than that of the secondary.
Short-circuited after power has been removed.

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

13. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
X.
The sum of the two capacitors.
Capacitance.

14. Where should grounding resistors be located?
60 Hertz
2000 watts
5:1
At the source transformer.

15. What type of 3-phase AC motor is used most often around a mine?
Reverse its rotation.
12 to 15 times a minute.
Nearly constant.
Squirrel-cage induction motor.

16. 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?
A step-up transformer.
150 turns.
Continuous.
The capacitors should be discharged.

17. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Because less current flowing at high voltage causes less line loss per kilowatt.
Grounded phase and ground fault devices were not operating.
Allow for metering voltage and Current.
Lower current and higher voltage.

18. Not true about AC power?
Alternating current.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
It provides good speed control.

19. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Reverse any two-phase leads.
1 amp.
75 turns.
Because less current flowing at high voltage causes less line loss per kilowatt.

20. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
75 turns.
At least two phases
The motor rotation is reversed.
Provides single-phase power to smaller loads such as lights - heaters - etc.

21. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Zero amps.
3 -979 Volts.
X.
7 -630 volts.

22. Which of the following does a squirrel cage induction motor have?
Check to make sure that the victim is not still in contact with the electricity.
A step-up transformer.
A grounding resistor.
Stator windings.

23. Three-phase AC underground cables must be provided with overcurrent protection using a...
Transformer
Circuit Breaker.
Short-circuited after power has been removed.
Two speeds

24. The standard frequency of alternating current used at a mine is...
Grounded phase and ground fault devices were not operating.
Squirrel-cage rotor.
An electrical shock hazard may exist.
60 Hertz

25. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
75 turns.
200 volts AC.
Squirrel-cage induction motor.

26. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
An electrical shock hazard may exist.
Derive a neutral for grounding purposes.
Clamp-on ammeter.

27. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A grounding resistor.
X.
15 feet off the ground.
They should be made by the same manufacturer.

28. A burn causing a blister is classified as a...
Nearly constant.
Second-degree burn.
Carotid pulse - which is located in the neck next to the Adam's apple.
An electrical shock hazard may exist.

29. 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?
Electro-magnetism for their operation.
A.C.
75 turns.
Alternating current.

30. What is a capacitor?
Reverse any two-phase leads.
Two speeds
A device used to store electrical energy.
5:1.

31. 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...
Stator windings.
Disconnect the frame-grounding conductor.
Tied together
5:1

32. 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.
5:1.
5:1
60 Hertz
Larger than that found in the primary winding.

33. 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...
12 to 15 times a minute.
They must be installed at least 7 feet above the ground.
Draw less current.
Inductance.

34. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Second-degree burn.
They should be made by the same manufacturer.
H terminals.

35. What is the danger when working around capacitors?
Squirrel-cage rotor.
Tied together
Circuit Breaker.
An electrical shock hazard may exist.

36. The secondary windings on a 10:1 step-down transformer will have a wire size...
Disconnect the frame-grounding conductor.
Shunted and taped
Larger than that found in the primary winding.
1 amp.

37. A transformer with a 1:1 ratio is usually a (an)...
5:1.
Isolation transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
A.C.

38. 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...
Draw less current.
The sum of the two capacitors.
Capacitance.
H terminals.

39. The combined capacitance of two capacitors in parallel is...
800 volts.
150 turns.
Draw less current.
The sum of the two capacitors.

40. 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?
277 volts.
Reverse any two-phase leads.
100 turns.
An electrical shock hazard may exist.

41. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Shunted and taped
200 volts AC.
Full-load - three-phase voltage.
The capacitors should be discharged.

42. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
A.C.
5:1
Carotid pulse - which is located in the neck next to the Adam's apple.

43. All transformers step voltage up or down by...
Kilovolt ampere (KVA).
Inductance.
100 volts.
Disconnect the frame-grounding conductor.

44. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
An electrical shock hazard may exist.
Four times less than that of the secondary.
Squirrel-cage induction motor.
Tied together

45. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Disconnect the frame-grounding conductor.
A grounding resistor.
Squirrel-cage rotor.
Short-circuited after power has been removed.

46. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Continuous.
Check to make sure that the victim is not still in contact with the electricity.
The current will read zero.
150 turns.

47. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Reverse its rotation.
The sum of the two capacitors.
Lower current and higher voltage

48. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
At the source transformer.
A grounding resistor.
A step-up transformer.
Allow for metering voltage and Current.

49. The property of an electrical circuit that opposes any change in voltage is called...
15 feet off the ground.
Capacitance.
Shunted and taped
3 -979 Volts.

50. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Clamp-on ammeter.
Allow for metering voltage and Current.
7 -630 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.