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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. 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.
60 cycles per second (60 Hertz).
Zero amps.
X.

2. What is a capacitor?
A grounding resistor.
Zero amps.
5:1
A device used to store electrical energy.

3. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
7 -630 volts.
Clamp-on ammeter.
Kilovolt ampere (KVA).
Circuit Breaker.

4. A wound-rotor induction motor has all the following EXCEPT...
Current that changes constantly in magnitude and periodically in direction.
Squirrel-cage rotor.
Stator windings.
Derive a neutral for grounding purposes.

5. 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
A step-up transformer.
An electromagnet.
A device used to store electrical energy.

6. Not an acceptable method for the installations of surface transformers?
An electromagnet.
X.
They must be installed at least 7 feet above the ground.
3 -979 Volts.

7. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Transformer
Transformers.
Zero amps.
Capacitance.

8. What type motor is a wound-rotor induction motor?
3 -979 Volts.
A.C.
12 to 15 times a minute.
H terminals.

9. 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...
60 Hertz
Squirrel-cage induction motor.
Inductance.
Draw less current.

10. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Zero amps.
The chest should rise or inflate.
Squirrel-cage rotor.
Derive a neutral for grounding purposes.

11. Define alternating current...
Zero amps.
Electro-magnetism for their operation.
Current changing constantly in magnitude and periodically in direction.
A device used to store electrical energy.

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

13. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Electro-magnetism for their operation.
A step-up transformer.
The motor rotation is reversed.

14. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Lower current and higher voltage.
Reverse any two-phase leads.
A grounding resistor.

15. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
Nearly constant.
25 feet.
5:1

16. A transformer has 1 -600 turns in the primary and 400 turns in the secondary. The primary voltage is 2 -400 volts. What is the secondary voltage?
Lower current and higher voltage.
600 volts.
A device used to store electrical energy.
A grounding resistor.

17. What should the duty rating of a grounding resistor be?
Clamp-on ammeter.
Second-degree burn.
Continuous.
A device used to store electrical energy.

18. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
At least two phases
A grounding resistor.
150 turns.
480 volts.

19. Three-phase AC underground cables must be provided with overcurrent protection using a...
Current changing constantly in magnitude and periodically in direction.
Circuit Breaker.
Lower current and higher voltage
60 Hertz

20. 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?
150 turns.
An electrical shock hazard may exist.
Grounded phase and ground fault devices were not operating.
Tied together

21. 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?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
15 feet off the ground.
Because less current flowing at high voltage causes less line loss per kilowatt.
75 turns.

22. 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?
It provides good speed control.
Electro-magnetism for their operation.
100 turns.
200 volts AC.

23. A burn causing a blister is classified as a...
Second-degree burn.
Alternating current.
Lower current and higher voltage.
Transformers.

24. How do you change the direction of a 3-phase AC motor?
3 -979 Volts.
Tied together
Reverse any two-phase leads.
An electrical shock hazard may exist.

25. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Second-degree burn.
60 cycles per second (60 Hertz).
A step-up transformer.
The capacitors should be discharged.

26. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Circuit Breaker.
Alternating current.
75 turns.
Two speeds

27. The size of a transformer is measured in...
75 turns.
Kilovolt ampere (KVA).
Second-degree burn.
The capacitors should be discharged.

28. Current that changes periodically in direction is...
Clamp-on ammeter.
The current will read zero.
The sum of the two capacitors.
Alternating current.

29. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Check to make sure that the victim is not still in contact with the electricity.
Capacitance.
No.6 AWG.
Derive a neutral for grounding purposes.

30. The main function of CT's and PT's on a main substation is to...
Derive a neutral for grounding purposes.
Allow for metering voltage and Current.
X.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

31. The primary leads of a single-phase transformer should be connected to the...
X.
Draw less current.
Current that changes constantly in magnitude and periodically in direction.
H terminals.

32. Which of the following does a squirrel cage induction motor have?
Hyperventilation.
Stator windings.
Reverse any two-phase leads.
Four times less than that of the secondary.

33. Find the turns ratio of a single-phase transformer with the following values: Primary power of 10 KW - secondary current of 200 amps - and primary voltage of 250 volts.
5:1.
100 volts.
Kilovolt ampere (KVA).
Tied together

34. Not true about AC power?
Nearly constant.
150 turns.
It provides good speed control.
Second-degree burn.

35. Where should grounding resistors be located?
H terminals.
Nearly constant.
At the source transformer.
12 to 15 times a minute.

36. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
Allow for metering voltage and Current.
Reverse any two-phase leads.
Current changing constantly in magnitude and periodically in direction.

37. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Potential transformer.
Carotid pulse - which is located in the neck next to the Adam's apple.
A device used to store electrical energy.

38. All transformers step voltage up or down by...
Inductance.
They should be made by the same manufacturer.
Stator windings.
Draw less current.

39. What is the first step to be followed in aiding a victim of electrical shock?
3 -979 Volts.
Check to make sure that the victim is not still in contact with the electricity.
Alternating current.
Inductance.

40. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Cut around clothing that has adhered to the burned area.
Circuit Breaker.
Grounded phase and ground fault devices were not operating.

41. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
Inductance.
H terminals.
75 turns.

42. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
7 -630 volts.
Grounded phase and ground fault devices were not operating.
X.
Alternating current.

43. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
At least two phases
Electro-magnetism for their operation.
Disconnect the frame-grounding conductor.
60 cycles per second (60 Hertz).

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

45. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Clamp-on ammeter.
15 feet off the ground.
25 feet.
Current changing constantly in magnitude and periodically in direction.

46. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Squirrel-cage induction motor.
The current will read zero.
It provides good speed control.
Transformers.

47. 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.
Disconnect the frame-grounding conductor.
Current changing constantly in magnitude and periodically in direction.
5:1
Reverse any two-phase leads.

48. What is the danger when working around capacitors?
Larger than that found in the primary winding.
An electrical shock hazard may exist.
Circuit Breaker.
Reverse its rotation.

49. Compared to the secondary of a loaded - step-down transformer - the primary has...
Squirrel-cage induction motor.
480 volts.
Lower current and higher voltage
Shunted and taped

50. The speed of an alternating current - squirrel-cage induction motor is...
100 turns.
Cut around clothing that has adhered to the burned area.
Allow for metering voltage and Current.
Nearly constant.