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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. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
A.C.
A grounding resistor.
The current will read zero.
15 feet off the ground.

2. What should the duty rating of a grounding resistor be?
Larger than that found in the primary winding.
H terminals.
Full-load - three-phase voltage.
Continuous.

3. 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?
100 turns.
At the source transformer.
75 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.

4. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Cut around clothing that has adhered to the burned area.
A step-up transformer.
Carotid pulse - which is located in the neck next to the Adam's apple.
The motor rotation is reversed.

5. 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...
Inductance.
Draw less current.
Reverse any two-phase leads.
Grounded phase and ground fault devices were not operating.

6. 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...
Short-circuited after power has been removed.
Isolation transformer.
600 volts.
Tied together

7. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
At the source transformer.
Circuit Breaker.
The capacitors should be discharged.

8. 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?
Stator windings.
800 volts.
75 turns.
Transformers.

9. The main function of CT's and PT's on a main substation is to...
15 feet off the ground.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Allow for metering voltage and Current.
The motor rotation is reversed.

10. What type of 3-phase AC motor is used most often around a mine?
They must be installed at least 7 feet above the ground.
Allow for metering voltage and Current.
Squirrel-cage induction motor.
Two speeds

11. All transformers step voltage up or down by...
The sum of the two capacitors.
Current changing constantly in magnitude and periodically in direction.
The motor rotation is reversed.
Inductance.

12. The standard frequency of power supplied by the power company is...
The current will read zero.
800 volts.
The capacitors should be discharged.
60 cycles per second (60 Hertz).

13. The size of a transformer is measured in...
Reverse its rotation.
15 feet off the ground.
Kilovolt ampere (KVA).
A step-up transformer.

14. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Squirrel-cage rotor.
Disconnect the frame-grounding conductor.
Reverse its rotation.
The chest should rise or inflate.

15. Not an acceptable method for the installations of surface transformers?
Cut around clothing that has adhered to the burned area.
15 feet off the ground.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
They must be installed at least 7 feet above the ground.

16. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Full-load - three-phase voltage.
Reverse any two-phase leads.
Reverse its rotation.
At least two phases

17. The secondary windings on a 10:1 step-down transformer will have a wire size...
Draw less current.
A step-up transformer.
Inductance.
Larger than that found in the primary winding.

18. Compared to the secondary of a loaded - step-down transformer - the primary has...
Grounded phase and ground fault devices were not operating.
Inductance.
Four times less than that of the secondary.
Lower current and higher voltage.

19. 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.
Zero amps.
2000 watts
Lower current and higher voltage.

20. The primary function of a power transformer is to provide...
Draw less current.
The sum of the two capacitors.
Continuous.
Full-load - three-phase voltage.

21. The property of an electrical circuit that opposes any change in voltage is called...
Circuit Breaker.
Short-circuited after power has been removed.
Because less current flowing at high voltage causes less line loss per kilowatt.
Capacitance.

22. What is the first step to be followed in aiding a victim of electrical shock?
Short-circuited after power has been removed.
Reverse any two-phase leads.
600 volts.
Check to make sure that the victim is not still in contact with the electricity.

23. What is the danger when working around capacitors?
Larger than that found in the primary winding.
150 turns.
An electrical shock hazard may exist.
H terminals.

24. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
At least two phases
Current that changes constantly in magnitude and periodically in direction.
Allow for metering voltage and Current.

25. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Reverse any two-phase leads.
Full-load - three-phase voltage.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

26. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
60 cycles per second (60 Hertz).
They must be installed at least 7 feet above the ground.
Two speeds

27. Not a symptom of electrical shock?.
75 turns.
Hyperventilation.
At least two phases
7 -630 volts.

28. 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.
150 turns.
1 amp.
Transformers.

29. Current that changes periodically in direction is...
1 amp.
Allow for metering voltage and Current.
Kilovolt ampere (KVA).
Alternating current.

30. When not connected to a load - the secondary leads of a current transformer should be...
100 turns.
Shunted and taped
No.6 AWG.
Zero amps.

31. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
800 volts.
X.
Lower current and higher voltage
No.6 AWG.

32. A solenoid coil is...
The sum of the two capacitors.
An electromagnet.
A.C.
12 to 15 times a minute.

33. The purpose of a zig-zag transformer is to...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Tied together
Derive a neutral for grounding purposes.
7 -630 volts.

34. Which of the following does a squirrel cage induction motor have?
Because less current flowing at high voltage causes less line loss per kilowatt.
Zero amps.
Stator windings.
5:1.

35. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
15 feet off the ground.
1 amp.
Alternating current.
100 turns.

36. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
25 feet.
Continuous.
Shunted and taped

37. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
600 volts.
They must be installed at least 7 feet above the ground.
25 feet.
The motor rotation is reversed.

38. What type motor is a wound-rotor induction motor?
Full-load - three-phase voltage.
Cut around clothing that has adhered to the burned area.
A.C.
Grounded phase and ground fault devices were not operating.

39. The property of an electric circuit that opposes any change in current is called...
Two speeds
At least two phases
Inductance.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

40. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
X.
Four times less than that of the secondary.
480 volts.
Current that changes constantly in magnitude and periodically in direction.

41. 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...
Nearly constant.
100 volts.
Draw less current.
Derive a neutral for grounding purposes.

42. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
277 volts.
A.C.
The chest should rise or inflate.
Because less current flowing at high voltage causes less line loss per kilowatt.

43. 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?
277 volts.
Grounded phase and ground fault devices were not operating.
Disconnect the frame-grounding conductor.
200 volts AC.

44. The primary leads of a single-phase transformer should be connected to the...
H terminals.
Reverse any two-phase leads.
75 turns.
An electromagnet.

45. 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?
75 turns.
No.6 AWG.
Squirrel-cage induction motor.
Grounded phase and ground fault devices were not operating.

46. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Capacitance.
X.
Lower current and higher voltage.

47. The standard frequency of alternating current used at a mine is...
Two speeds
Alternating current.
5:1
60 Hertz

48. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
2000 watts
75 turns.
Second-degree burn.
Continuous.

49. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
Allow for metering voltage and Current.
Hyperventilation.
Full-load - three-phase voltage.

50. 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?
Tied together
200 volts AC.
3 -979 Volts.
12 to 15 times a minute.