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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 following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Clamp-on ammeter.
15 feet off the ground.
They must be installed at least 7 feet above the ground.
Two speeds

2. 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?
Short-circuited after power has been removed.
1 amp.
75 turns.
Clamp-on ammeter.

3. What type of 3-phase AC motor is used most often around a mine?
At least two phases
Four times less than that of the secondary.
Second-degree burn.
Squirrel-cage induction motor.

4. Three-phase AC underground cables must be provided with overcurrent protection using a...
Zero amps.
Circuit Breaker.
A step-up transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.

5. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
H terminals.
They must be installed at least 7 feet above the ground.
2000 watts
Larger than that found in the primary winding.

6. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
They must be installed at least 7 feet above the ground.
Electro-magnetism for their operation.
Circuit Breaker.

7. Alternating current may be defined as...
60 Hertz
Provides single-phase power to smaller loads such as lights - heaters - etc.
An electromagnet.
Current that changes constantly in magnitude and periodically in direction.

8. Not true about AC power?
Because less current flowing at high voltage causes less line loss per kilowatt.
It provides good speed control.
The current will read zero.
An electrical shock hazard may exist.

9. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
600 volts.
Grounded phase and ground fault devices were not operating.
Inductance.
No.6 AWG.

10. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Derive a neutral for grounding purposes.
Grounded phase and ground fault devices were not operating.
They should be made by the same manufacturer.
Zero amps.

11. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Transformer
60 cycles per second (60 Hertz).
15 feet off the ground.
600 volts.

12. Not a symptom of electrical shock?.
Draw less current.
Hyperventilation.
An electrical shock hazard may exist.
Reverse any two-phase leads.

13. How do you change the direction of a 3-phase AC motor?
Check to make sure that the victim is not still in contact with the electricity.
Reverse any two-phase leads.
7 -630 volts.
Isolation transformer.

14. The secondary windings on a 10:1 step-down transformer will have a wire size...
Stator windings.
They should be made by the same manufacturer.
Larger than that found in the primary winding.
The motor rotation is reversed.

15. The property of an electric circuit that opposes any change in current is called...
Inductance.
Circuit Breaker.
Because less current flowing at high voltage causes less line loss per kilowatt.
Nearly constant.

16. 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...
100 volts.
Circuit Breaker.
75 turns.
The current will read zero.

17. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Derive a neutral for grounding purposes.
The chest should rise or inflate.
Squirrel-cage rotor.
Second-degree burn.

18. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Transformers.
Current changing constantly in magnitude and periodically in direction.
A grounding resistor.
12 to 15 times a minute.

19. What is the danger when working around capacitors?
Circuit Breaker.
Continuous.
An electrical shock hazard may exist.
A grounding resistor.

20. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Squirrel-cage induction motor.
480 volts.
60 cycles per second (60 Hertz).
Zero amps.

21. Compared to the secondary of a loaded - step-down transformer - the primary has...
Transformers.
Draw less current.
Lower current and higher voltage
Transformer

22. Which of the following does a squirrel cage induction motor have?
Stator windings.
A.C.
An electromagnet.
Clamp-on ammeter.

23. 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?
The current will read zero.
Electro-magnetism for their operation.
3 -979 Volts.
Clamp-on ammeter.

24. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Lower current and higher voltage.
Two speeds
At least two phases
Squirrel-cage induction motor.

25. Not an acceptable method for the installations of surface transformers?
Current changing constantly in magnitude and periodically in direction.
They must be installed at least 7 feet above the ground.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
60 Hertz

26. What should the duty rating of a grounding resistor be?
200 volts AC.
Continuous.
Transformer
Cut around clothing that has adhered to the burned area.

27. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
200 volts AC.
Continuous.
Inductance.

28. The size of a transformer is measured in...
H terminals.
Four times less than that of the secondary.
Kilovolt ampere (KVA).
3 -979 Volts.

29. A solenoid coil is...
60 Hertz
An electromagnet.
Shunted and taped
Inductance.

30. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
3 -979 Volts.
They should be made by the same manufacturer.
Reverse any two-phase leads.

31. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Carotid pulse - which is located in the neck next to the Adam's apple.
The capacitors should be discharged.
At least two phases
Four times less than that of the secondary.

32. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Continuous.
Full-load - three-phase voltage.
The current will read zero.
No.6 AWG.

33. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Tied together
The capacitors should be discharged.
At least two phases
They should be made by the same manufacturer.

34. At what rate should mouth-to-mouth resuscitation be applied?
800 volts.
Isolation transformer.
Reverse its rotation.
12 to 15 times a minute.

35. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Draw less current.
60 cycles per second (60 Hertz).
277 volts.

36. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
Clamp-on ammeter.
60 cycles per second (60 Hertz).
Current changing constantly in magnitude and periodically in direction.

37. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Transformer
A step-up transformer.
15 feet off the ground.
Four times less than that of the secondary.

38. 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.
7 -630 volts.
Current changing constantly in magnitude and periodically in direction.
Isolation transformer.

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.
A.C.
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.

40. What type motor is a wound-rotor induction motor?
Reverse any two-phase leads.
A.C.
12 to 15 times a minute.
Kilovolt ampere (KVA).

41. What steps up or steps down AC voltage?
100 turns.
Reverse its rotation.
Shunted and taped
Transformer

42. 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.
5:1
Capacitance.
Allow for metering voltage and Current.

43. The purpose of a zig-zag transformer is to...
Inductance.
A grounding resistor.
200 volts AC.
Derive a neutral for grounding purposes.

44. The property of an electrical circuit that opposes any change in voltage is called...
100 volts.
X.
15 feet off the ground.
Capacitance.

45. 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?
200 volts AC.
Tied together
5:1.
2000 watts

46. A burn causing a blister is classified as a...
600 volts.
An electromagnet.
Second-degree burn.
1 amp.

47. What is the first step to be followed in aiding a victim of electrical shock?
A.C.
The sum of the two capacitors.
Inductance.
Check to make sure that the victim is not still in contact with the electricity.

48. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
An electrical shock hazard may exist.
Short-circuited after power has been removed.
Carotid pulse - which is located in the neck next to the Adam's apple.
7 -630 volts.

49. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
3 -979 Volts.
X.
Zero amps.
Current that changes constantly in magnitude and periodically in direction.

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?
Stator windings.
75 turns.
The current will read zero.
Electro-magnetism for their operation.