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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. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Short-circuited after power has been removed.
The current will read zero.
Current that changes constantly in magnitude and periodically in direction.
The capacitors should be discharged.

2. What is a capacitor?
800 volts.
Shunted and taped
A device used to store electrical energy.
A step-up transformer.

3. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
The motor rotation is reversed.
Transformer
Short-circuited after power has been removed.

4. What steps up or steps down AC voltage?
X.
Squirrel-cage induction motor.
Stator windings.
Transformer

5. 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?
Hyperventilation.
It provides good speed control.
Squirrel-cage induction motor.
75 turns.

6. A control power transformer...
Clamp-on ammeter.
5:1
Provides single-phase power to smaller loads such as lights - heaters - etc.
100 turns.

7. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
A device used to store electrical energy.
Draw less current.
Isolation transformer.
Grounded phase and ground fault devices were not operating.

8. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
480 volts.
2000 watts
A.C.
25 feet.

9. High voltage is used to transmit power over long distances...
Circuit Breaker.
Lower current and higher voltage.
Because less current flowing at high voltage causes less line loss per kilowatt.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

10. To protect against over-current in a three-phase circuit over-current protection must be provided for...
75 turns.
At least two phases
Because less current flowing at high voltage causes less line loss per kilowatt.
An electrical shock hazard may exist.

11. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Four times less than that of the secondary.
100 volts.
Short-circuited after power has been removed.
Isolation transformer.

12. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
60 cycles per second (60 Hertz).
12 to 15 times a minute.
Draw less current.
The motor rotation is reversed.

13. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
It provides good speed control.
Disconnect the frame-grounding conductor.
480 volts.
At least two phases

14. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Allow for metering voltage and Current.
Full-load - three-phase voltage.
X.
A grounding resistor.

15. The size of a transformer is measured in...
Reverse any two-phase leads.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Kilovolt ampere (KVA).
150 turns.

16. 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...
Tied together
Current changing constantly in magnitude and periodically in direction.
Inductance.
Lower current and higher voltage

17. The purpose of a zig-zag transformer is to...
15 feet off the ground.
Allow for metering voltage and Current.
150 turns.
Derive a neutral for grounding purposes.

18. When not connected to a load - the secondary leads of a current transformer should be...
Carotid pulse - which is located in the neck next to the Adam's apple.
Shunted and taped
Kilovolt ampere (KVA).
Derive a neutral for grounding purposes.

19. Which of the following does a squirrel cage induction motor have?
At the source transformer.
Transformer
Stator windings.
Second-degree burn.

20. All transformers step voltage up or down by...
Inductance.
Disconnect the frame-grounding conductor.
7 -630 volts.
277 volts.

21. What is the first step to be followed in aiding a victim of electrical shock?
X.
An electromagnet.
2000 watts
Check to make sure that the victim is not still in contact with the electricity.

22. At what rate should mouth-to-mouth resuscitation be applied?
3 -979 Volts.
12 to 15 times a minute.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Current changing constantly in magnitude and periodically in direction.

23. 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
Continuous.
Two speeds
2000 watts

24. The speed of an alternating current - squirrel-cage induction motor is...
They must be installed at least 7 feet above the ground.
Shunted and taped
5:1
Nearly constant.

25. Compared to the secondary of a loaded - step-down transformer - the primary has...
100 volts.
Check to make sure that the victim is not still in contact with the electricity.
Zero amps.
Lower current and higher voltage

26. A burn causing a blister is classified as a...
H terminals.
Stator windings.
Second-degree burn.
The motor rotation is reversed.

27. The combined capacitance of two capacitors in parallel is...
Hyperventilation.
5:1.
The sum of the two capacitors.
The current will read zero.

28. The property of an electrical circuit that opposes any change in voltage is called...
H terminals.
Capacitance.
25 feet.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

29. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Two speeds
2000 watts
Circuit Breaker.

30. 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?
No.6 AWG.
100 turns.
3 -979 Volts.
Squirrel-cage induction motor.

31. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Second-degree burn.
277 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Draw less current.

32. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Inductance.
Disconnect the frame-grounding conductor.
2000 watts
H terminals.

33. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Draw less current.
Two speeds
100 volts.
Second-degree burn.

34. 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?
Allow for metering voltage and Current.
200 volts AC.
15 feet off the ground.
Nearly constant.

35. 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...
Lower current and higher voltage
Draw less current.
A.C.
Circuit Breaker.

36. Current that changes periodically in direction is...
At least two phases
75 turns.
12 to 15 times a minute.
Alternating current.

37. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Check to make sure that the victim is not still in contact with the electricity.
The capacitors should be discharged.
277 volts.

38. 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?
Reverse any two-phase leads.
12 to 15 times a minute.
75 turns.
277 volts.

39. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Circuit Breaker.
X.
Full-load - three-phase voltage.
The current will read zero.

40. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
Carotid pulse - which is located in the neck next to the Adam's apple.
Current changing constantly in magnitude and periodically in direction.
75 turns.

41. The standard frequency of alternating current used at a mine is...
A.C.
60 Hertz
Allow for metering voltage and Current.
At the source transformer.

42. 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?
Inductance.
A grounding resistor.
An electromagnet.
150 turns.

43. What should the duty rating of a grounding resistor be?
Four times less than that of the secondary.
An electromagnet.
X.
Continuous.

44. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
Current changing constantly in magnitude and periodically in direction.
Cut around clothing that has adhered to the burned area.
Second-degree burn.

45. Alternating current may be defined as...
3 -979 Volts.
Current changing constantly in magnitude and periodically in direction.
X.
Current that changes constantly in magnitude and periodically in direction.

46. Current transformers - or CT's - are used to...
Circuit Breaker.
12 to 15 times a minute.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Current changing constantly in magnitude and periodically in direction.

47. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Full-load - three-phase voltage.
It provides good speed control.
A.C.
7 -630 volts.

48. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
800 volts.
75 turns.
Four times less than that of the secondary.
Lower current and higher voltage

49. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Nearly constant.
They should be made by the same manufacturer.
Check to make sure that the victim is not still in contact with the electricity.

50. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Kilovolt ampere (KVA).
Disconnect the frame-grounding conductor.
At least two phases
No.6 AWG.