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Test your basic knowledge |

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. 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...
X.
A grounding resistor.
Squirrel-cage induction motor.
100 volts.

2. A control power transformer...
15 feet off the ground.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Capacitance.
Disconnect the frame-grounding conductor.

3. All transformers step voltage up or down by...
Tied together
12 to 15 times a minute.
Lower current and higher voltage
Inductance.

4. 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?
75 turns.
Allow for metering voltage and Current.
200 volts AC.
Kilovolt ampere (KVA).

5. AC voltage is raised or lowered by means of...
Electro-magnetism for their operation.
15 feet off the ground.
Transformers.
60 Hertz

6. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
100 turns.
Tied together
Continuous.

7. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
1 amp.
Tied together
The motor rotation is reversed.

8. A transformer with a 1:1 ratio is usually a (an)...
75 turns.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Cut around clothing that has adhered to the burned area.
Isolation transformer.

9. 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?
600 volts.
100 turns.
277 volts.
3 -979 Volts.

10. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Because less current flowing at high voltage causes less line loss per kilowatt.
The chest should rise or inflate.
Second-degree burn.
Potential transformer.

11. What is the danger when working around capacitors?
An electrical shock hazard may exist.
An electromagnet.
The current will read zero.
Lower current and higher voltage.

12. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
60 cycles per second (60 Hertz).
An electromagnet.
Draw less current.

13. The main function of CT's and PT's on a main substation is to...
Current changing constantly in magnitude and periodically in direction.
Allow for metering voltage and Current.
Two speeds
Short-circuited after power has been removed.

14. Compared to the secondary of a loaded - step-down transformer - the primary has...
The current will read zero.
A step-up transformer.
Lower current and higher voltage.
Draw less current.

15. How do you change the direction of a 3-phase AC motor?
Zero amps.
75 turns.
Reverse any two-phase leads.
277 volts.

16. The speed of an alternating current - squirrel-cage induction motor is...
480 volts.
60 cycles per second (60 Hertz).
Nearly constant.
Grounded phase and ground fault devices were not operating.

17. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Two speeds
The motor rotation is reversed.
Inductance.
1 amp.

18. What steps up or steps down AC voltage?
480 volts.
Inductance.
Transformer
Carotid pulse - which is located in the neck next to the Adam's apple.

19. Compared to the secondary of a loaded - step-down transformer - the primary has...
75 turns.
Lower current and higher voltage
100 turns.
5:1

20. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Full-load - three-phase voltage.
No.6 AWG.
5:1.
7 -630 volts.

21. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Check to make sure that the victim is not still in contact with the electricity.
They should be made by the same manufacturer.
Lower current and higher voltage.
Grounded phase and ground fault devices were not operating.

22. Alternating current may be defined as...
Kilovolt ampere (KVA).
Reverse its rotation.
Current that changes constantly in magnitude and periodically in direction.
At least two phases

23. The combined capacitance of two capacitors in parallel is...
Draw less current.
Tied together
The sum of the two capacitors.
Reverse any two-phase leads.

24. A wound-rotor induction motor has all the following EXCEPT...
They should be made by the same manufacturer.
Squirrel-cage rotor.
It provides good speed control.
75 turns.

25. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Reverse its rotation.
Current that changes constantly in magnitude and periodically in direction.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
60 cycles per second (60 Hertz).

26. A solenoid coil is...
1 amp.
480 volts.
An electromagnet.
Electro-magnetism for their operation.

27. The standard frequency of power supplied by the power company is...
At the source transformer.
The sum of the two capacitors.
Current that changes constantly in magnitude and periodically in direction.
60 cycles per second (60 Hertz).

28. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Carotid pulse - which is located in the neck next to the Adam's apple.
Draw less current.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Zero amps.

29. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
2000 watts
Draw less current.
Two speeds
25 feet.

30. 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...
Shunted and taped
Grounded phase and ground fault devices were not operating.
Isolation transformer.
Draw less current.

31. 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?
800 volts.
Inductance.
Zero amps.
Second-degree burn.

32. 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.
Nearly constant.
The current will read zero.
15 feet off the ground.

33. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Isolation transformer.
Disconnect the frame-grounding conductor.
Lower current and higher voltage
Allow for metering voltage and Current.

34. Not an acceptable method for the installations of surface transformers?
Grounded phase and ground fault devices were not operating.
Stator windings.
75 turns.
They must be installed at least 7 feet above the ground.

35. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
Larger than that found in the primary winding.
A.C.
Current that changes constantly in magnitude and periodically in direction.

36. 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
The sum of the two capacitors.
Draw less current.
277 volts.

37. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
A step-up transformer.
No.6 AWG.
Derive a neutral for grounding purposes.
Four times less than that of the secondary.

38. Not true about AC power?
Transformer
Reverse any two-phase leads.
Electro-magnetism for their operation.
It provides good speed control.

39. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Inductance.
Short-circuited after power has been removed.
480 volts.
100 volts.

40. Current transformers - or CT's - are used to...
No.6 AWG.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Draw less current.
The sum of the two capacitors.

41. A burn causing a blister is classified as a...
600 volts.
Disconnect the frame-grounding conductor.
Second-degree burn.
75 turns.

42. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
12 to 15 times a minute.
A device used to store electrical energy.
Lower current and higher voltage.

43. Operating coils - motors - transformers - relays and solenoids depend upon...
At the source transformer.
Reverse any two-phase leads.
H terminals.
Electro-magnetism for their operation.

44. The secondary windings on a 10:1 step-down transformer will have a wire size...
Shunted and taped
Larger than that found in the primary winding.
Reverse its rotation.
Second-degree burn.

45. 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...
H terminals.
They must be installed at least 7 feet above the ground.
Short-circuited after power has been removed.
Draw less current.

46. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
Lower current and higher voltage.
1 amp.
Allow for metering voltage and Current.

47. To protect against over-current in a three-phase circuit over-current protection must be provided for...
800 volts.
Nearly constant.
The capacitors should be discharged.
At least two phases

48. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Two speeds
277 volts.
The current will read zero.
H terminals.

49. The size of a transformer is measured in...
A step-up transformer.
Kilovolt ampere (KVA).
Derive a neutral for grounding purposes.
60 Hertz

50. If any two-phase wires are reversed on a three-phase motor - the motor will...
Second-degree burn.
5:1.
A device used to store electrical energy.
Reverse its rotation.