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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 secondary windings on a 10:1 step-down transformer will have a wire size...
25 feet.
60 cycles per second (60 Hertz).
Larger than that found in the primary winding.
Lower current and higher voltage.

2. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Reverse its rotation.
The current will read zero.
Zero amps.

3. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
The current will read zero.
Inductance.
1 amp.

4. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Shunted and taped
The current will read zero.
15 feet off the ground.
The chest should rise or inflate.

5. 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.
480 volts.
75 turns.
The capacitors should be discharged.

6. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
Reverse its rotation.
Zero amps.
Draw less current.

7. 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...
They should be made by the same manufacturer.
Transformers.
Tied together
Hyperventilation.

8. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
A.C.
An electrical shock hazard may exist.
100 volts.

9. Three-phase AC underground cables must be provided with overcurrent protection using a...
2000 watts
1 amp.
Current changing constantly in magnitude and periodically in direction.
Circuit Breaker.

10. Current that changes periodically in direction is...
Transformers.
Alternating current.
The motor rotation is reversed.
Inductance.

11. Not an acceptable method for the installations of surface transformers?
The chest should rise or inflate.
They must be installed at least 7 feet above the ground.
Current that changes constantly in magnitude and periodically in direction.
7 -630 volts.

12. The primary leads of a single-phase transformer should be connected to the...
60 Hertz
H terminals.
25 feet.
Carotid pulse - which is located in the neck next to the Adam's apple.

13. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Circuit Breaker.
15 feet off the ground.
An electromagnet.
2000 watts

14. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
1 amp.
277 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
Grounded phase and ground fault devices were not operating.

15. The property of an electric circuit that opposes any change in current is called...
Electro-magnetism for their operation.
Grounded phase and ground fault devices were not operating.
Inductance.
Lower current and higher voltage.

16. 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?
An electrical shock hazard may exist.
75 turns.
Shunted and taped
200 volts AC.

17. The standard frequency of alternating current used at a mine is...
Circuit Breaker.
60 Hertz
Hyperventilation.
75 turns.

18. 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.
Draw less current.
Transformer
7 -630 volts.

19. Alternating current may be defined as...
Clamp-on ammeter.
Full-load - three-phase voltage.
12 to 15 times a minute.
Current that changes constantly in magnitude and periodically in direction.

20. The combined capacitance of two capacitors in parallel is...
5:1
The sum of the two capacitors.
Clamp-on ammeter.
Nearly constant.

21. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Lower current and higher voltage.
2000 watts
No.6 AWG.
Derive a neutral for grounding purposes.

22. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Continuous.
60 Hertz
At least two phases
Clamp-on ammeter.

23. What is the first step to be followed in aiding a victim of electrical shock?
Check to make sure that the victim is not still in contact with the electricity.
Cut around clothing that has adhered to the burned area.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
H terminals.

24. 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.
200 volts AC.
The capacitors should be discharged.
They must be installed at least 7 feet above the ground.

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

26. 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?
Clamp-on ammeter.
12 to 15 times a minute.
3 -979 Volts.
At least two phases

27. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
They should be made by the same manufacturer.
At the source transformer.
Kilovolt ampere (KVA).

28. 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?
Transformer
100 turns.
150 turns.
Current changing constantly in magnitude and periodically in direction.

29. Not a symptom of electrical shock?.
Inductance.
Hyperventilation.
Kilovolt ampere (KVA).
200 volts AC.

30. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
X.
Tied together
The motor rotation is reversed.
7 -630 volts.

31. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Reverse any two-phase leads.
An electromagnet.
X.
75 turns.

32. Not true about AC power?
Current changing constantly in magnitude and periodically in direction.
Full-load - three-phase voltage.
It provides good speed control.
7 -630 volts.

33. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
7 -630 volts.
The chest should rise or inflate.
Two speeds
Draw less current.

34. Current in an AC circuit may be measured by...
Because less current flowing at high voltage causes less line loss per kilowatt.
Clamp-on ammeter.
Squirrel-cage induction motor.
150 turns.

35. 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?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
75 turns.
No.6 AWG.
Draw less current.

36. A transformer with a 1:1 ratio is usually a (an)...
Inductance.
Allow for metering voltage and Current.
Larger than that found in the primary winding.
Isolation transformer.

37. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
Larger than that found in the primary winding.
100 turns.
A grounding resistor.

38. All transformers step voltage up or down by...
Inductance.
5:1.
Lower current and higher voltage
100 volts.

39. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Larger than that found in the primary winding.
75 turns.
Nearly constant.
2000 watts

40. 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.
5:1.
150 turns.
Draw less current.

41. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
15 feet off the ground.
7 -630 volts.
Draw less current.
200 volts AC.

42. High voltage is used to transmit power over long distances...
1 amp.
At the source transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.
3 -979 Volts.

43. The property of an electrical circuit that opposes any change in voltage is called...
Reverse any two-phase leads.
They should be made by the same manufacturer.
Second-degree burn.
Capacitance.

44. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
277 volts.
Derive a neutral for grounding purposes.
At least two phases

45. 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?
Zero amps.
The motor rotation is reversed.
800 volts.
An electromagnet.

46. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Derive a neutral for grounding purposes.
Inductance.
Larger than that found in the primary winding.
The chest should rise or inflate.

47. Where should grounding resistors be located?
150 turns.
Capacitance.
Derive a neutral for grounding purposes.
At the source transformer.

48. Current transformers - or CT's - are used to...
Full-load - three-phase voltage.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
75 turns.

49. 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...
Grounded phase and ground fault devices were not operating.
Draw less current.
Larger than that found in the primary winding.
150 turns.

50. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
The chest should rise or inflate.
100 turns.
Squirrel-cage rotor.