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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. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
7 -630 volts.
Grounded phase and ground fault devices were not operating.
Inductance.

2. The primary function of a power transformer is to provide...
Draw less current.
Clamp-on ammeter.
Circuit Breaker.
Full-load - three-phase voltage.

3. Not true about AC power?
Squirrel-cage induction motor.
The motor rotation is reversed.
It provides good speed control.
Current changing constantly in magnitude and periodically in direction.

4. A burn causing a blister is classified as a...
Second-degree burn.
Grounded phase and ground fault devices were not operating.
600 volts.
Allow for metering voltage and Current.

5. Current transformers - or CT's - are used to...
Reverse any two-phase leads.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Reverse its rotation.
The sum of the two capacitors.

6. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
Four times less than that of the secondary.
They must be installed at least 7 feet above the ground.
200 volts AC.

7. Compared to the secondary of a loaded - step-down transformer - the primary has...
Because less current flowing at high voltage causes less line loss per kilowatt.
Current changing constantly in magnitude and periodically in direction.
3 -979 Volts.
Lower current and higher voltage

8. The primary leads of a single-phase transformer should be connected to the...
Larger than that found in the primary winding.
H terminals.
Alternating current.
60 cycles per second (60 Hertz).

9. A transformer with a 1:1 ratio is usually a (an)...
5:1.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
100 volts.
Isolation transformer.

10. Three-phase AC underground cables must be provided with overcurrent protection using a...
Circuit Breaker.
The motor rotation is reversed.
A device used to store electrical energy.
Reverse its rotation.

11. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
Shunted and taped
Continuous.
Current that changes constantly in magnitude and periodically in direction.

12. The purpose of a zig-zag transformer is to...
Disconnect the frame-grounding conductor.
150 turns.
600 volts.
Derive a neutral for grounding purposes.

13. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
800 volts.
Grounded phase and ground fault devices were not operating.
Reverse its rotation.
150 turns.

14. The property of an electrical circuit that opposes any change in voltage is called...
Inductance.
Lower current and higher voltage
Capacitance.
200 volts AC.

15. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
12 to 15 times a minute.
The motor rotation is reversed.
5:1
Kilovolt ampere (KVA).

16. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Lower current and higher voltage
100 volts.
Cut around clothing that has adhered to the burned area.
Four times less than that of the secondary.

17. 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?
Provides single-phase power to smaller loads such as lights - heaters - etc.
Derive a neutral for grounding purposes.
75 turns.
277 volts.

18. Where should grounding resistors be located?
An electromagnet.
At the source transformer.
An electrical shock hazard may exist.
5:1.

19. What is a capacitor?
At least two phases
A device used to store electrical energy.
1 amp.
No.6 AWG.

20. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Carotid pulse - which is located in the neck next to the Adam's apple.
5:1
Short-circuited after power has been removed.
200 volts AC.

21. The size of a transformer is measured in...
Kilovolt ampere (KVA).
Grounded phase and ground fault devices were not operating.
Disconnect the frame-grounding conductor.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

22. All transformers step voltage up or down by...
100 turns.
60 Hertz
600 volts.
Inductance.

23. Not a symptom of electrical shock?.
Hyperventilation.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Capacitance.
Draw less current.

24. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Zero amps.
A step-up transformer.
Nearly constant.
Isolation transformer.

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

26. Current in an AC circuit may be measured by...
480 volts.
Two speeds
Clamp-on ammeter.
Second-degree burn.

27. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Inductance.
Carotid pulse - which is located in the neck next to the Adam's apple.
At the source transformer.
15 feet off the ground.

28. 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...
A grounding resistor.
Stator windings.
The motor rotation is reversed.
Tied together

29. The transformer used only to measure voltage is a...
75 turns.
277 volts.
Potential transformer.
Hyperventilation.

30. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Four times less than that of the secondary.
Inductance.
Kilovolt ampere (KVA).
X.

31. The property of an electric circuit that opposes any change in current is called...
Four times less than that of the secondary.
Disconnect the frame-grounding conductor.
Second-degree burn.
Inductance.

32. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Draw less current.
The chest should rise or inflate.

33. Alternating current may be defined as...
The motor rotation is reversed.
At the source transformer.
Tied together
Current that changes constantly in magnitude and periodically in direction.

34. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
The current will read zero.
Lower current and higher voltage.
15 feet off the ground.

35. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Grounded phase and ground fault devices were not operating.
60 cycles per second (60 Hertz).
Capacitance.
25 feet.

36. AC voltage is raised or lowered by means of...
3 -979 Volts.
150 turns.
Transformers.
Two speeds

37. What is the first step to be followed in aiding a victim of electrical shock?
H terminals.
Squirrel-cage rotor.
Check to make sure that the victim is not still in contact with the electricity.
A device used to store electrical energy.

38. The secondary windings on a 10:1 step-down transformer will have a wire size...
Stator windings.
Cut around clothing that has adhered to the burned area.
Reverse any two-phase leads.
Larger than that found in the primary winding.

39. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
They should be made by the same manufacturer.
Zero amps.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Reverse any two-phase leads.

40. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
Second-degree burn.
Circuit Breaker.
Larger than that found in the primary winding.

41. How do you change the direction of a 3-phase AC motor?
75 turns.
At least two phases
It provides good speed control.
Reverse any two-phase leads.

42. When not connected to a load - the secondary leads of a current transformer should be...
200 volts AC.
Shunted and taped
Hyperventilation.
100 turns.

43. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
H terminals.
An electrical shock hazard may exist.
Two speeds
The sum of the two capacitors.

44. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Disconnect the frame-grounding conductor.
Lower current and higher voltage
Zero amps.
2000 watts

45. A wound-rotor induction motor has all the following EXCEPT...
75 turns.
Squirrel-cage rotor.
Tied together
2000 watts

46. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
25 feet.
5:1.
100 turns.

47. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Reverse its rotation.
A grounding resistor.
Draw less current.

48. What is the danger when working around capacitors?
Clamp-on ammeter.
An electrical shock hazard may exist.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Cut around clothing that has adhered to the burned area.

49. A solenoid coil is...
15 feet off the ground.
An electromagnet.
Two speeds
H terminals.

50. 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.
12 to 15 times a minute.
Transformers.
Nearly constant.

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