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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?
75 turns.
Disconnect the frame-grounding conductor.
At least two phases
Tied together

2. Current in an AC circuit may be measured by...
Squirrel-cage rotor.
1 amp.
Because less current flowing at high voltage causes less line loss per kilowatt.
Clamp-on ammeter.

3. 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...
Zero amps.
Draw less current.
Capacitance.
An electrical shock hazard may exist.

4. When not connected to a load - the secondary leads of a current transformer should be...
Kilovolt ampere (KVA).
Carotid pulse - which is located in the neck next to the Adam's apple.
Shunted and taped
Because less current flowing at high voltage causes less line loss per kilowatt.

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.
Kilovolt ampere (KVA).
The current will read zero.
Transformer

6. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
A.C.
Continuous.
Two speeds
Electro-magnetism for their operation.

7. Three-phase AC underground cables must be provided with overcurrent protection using a...
Second-degree burn.
Circuit Breaker.
Continuous.
Grounded phase and ground fault devices were not operating.

8. What is a capacitor?
Shunted and taped
Capacitance.
A device used to store electrical energy.
600 volts.

9. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
The sum of the two capacitors.
Inductance.
Provides single-phase power to smaller loads such as lights - heaters - etc.

10. What type of 3-phase AC motor is used most often around a mine?
Full-load - three-phase voltage.
Squirrel-cage induction motor.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Hyperventilation.

11. A transformer with a 1:1 ratio is usually a (an)...
A grounding resistor.
At the source transformer.
Isolation transformer.
Grounded phase and ground fault devices were not operating.

12. AC voltage is raised or lowered by means of...
5:1
A.C.
Four times less than that of the secondary.
Transformers.

13. What steps up or steps down AC voltage?
Transformer
Draw less current.
An electromagnet.
They must be installed at least 7 feet above the ground.

14. 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?
An electromagnet.
100 turns.
2000 watts
5:1

15. All transformers step voltage up or down by...
A grounding resistor.
Four times less than that of the secondary.
Inductance.
Derive a neutral for grounding purposes.

16. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Zero amps.
Capacitance.
Derive a neutral for grounding purposes.
X.

17. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
3 -979 Volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
Electro-magnetism for their operation.
Grounded phase and ground fault devices were not operating.

18. Not true about AC power?
At the source transformer.
75 turns.
Inductance.
It provides good speed control.

19. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
At least two phases
Transformer
75 turns.

20. 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?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
1 amp.
At least two phases
3 -979 Volts.

21. A wound-rotor induction motor has all the following EXCEPT...
Draw less current.
Squirrel-cage induction motor.
Squirrel-cage rotor.
Lower current and higher voltage

22. What is the danger when working around capacitors?
Clamp-on ammeter.
Reverse any two-phase leads.
It provides good speed control.
An electrical shock hazard may exist.

23. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Short-circuited after power has been removed.
1 amp.
5:1.
277 volts.

24. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The sum of the two capacitors.
60 Hertz
The motor rotation is reversed.
The current will read zero.

25. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
Grounded phase and ground fault devices were not operating.
An electromagnet.
Cut around clothing that has adhered to the burned area.

26. 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.
150 turns.
Stator windings.
The current will read zero.
5:1.

27. The main function of CT's and PT's on a main substation is to...
Current that changes constantly in magnitude and periodically in direction.
Lower current and higher voltage
Allow for metering voltage and Current.
They should be made by the same manufacturer.

28. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Cut around clothing that has adhered to the burned area.
75 turns.
A grounding resistor.
Current that changes constantly in magnitude and periodically in direction.

29. The purpose of a zig-zag transformer is to...
They must be installed at least 7 feet above the ground.
Carotid pulse - which is located in the neck next to the Adam's apple.
3 -979 Volts.
Derive a neutral for grounding purposes.

30. The transformer used only to measure voltage is a...
Potential transformer.
At least two phases
Reverse any two-phase leads.
They should be made by the same manufacturer.

31. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Grounded phase and ground fault devices were not operating.
They must be installed at least 7 feet above the ground.
7 -630 volts.
The chest should rise or inflate.

32. A solenoid coil is...
The motor rotation is reversed.
An electromagnet.
A device used to store electrical energy.
Alternating current.

33. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
The current will read zero.
Hyperventilation.
Clamp-on ammeter.

34. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Draw less current.
H terminals.
Second-degree burn.
No.6 AWG.

35. 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?
Shunted and taped
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
100 turns.
800 volts.

36. How should clothing be removed from a burn?
Potential transformer.
200 volts AC.
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.

37. 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
12 to 15 times a minute.
1 amp.
The capacitors should be discharged.

38. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Squirrel-cage induction motor.
Transformers.
Four times less than that of the secondary.
They must be installed at least 7 feet above the ground.

39. Alternating current may be defined as...
75 turns.
Current that changes constantly in magnitude and periodically in direction.
Zero amps.
Clamp-on ammeter.

40. What should the duty rating of a grounding resistor be?
75 turns.
Transformer
H terminals.
Continuous.

41. A control power transformer...
A device used to store electrical energy.
An electrical shock hazard may exist.
Provides single-phase power to smaller loads such as lights - heaters - etc.
100 volts.

42. The property of an electrical circuit that opposes any change in voltage is called...
The chest should rise or inflate.
No.6 AWG.
Cut around clothing that has adhered to the burned area.
Capacitance.

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

44. Operating coils - motors - transformers - relays and solenoids depend upon...
Circuit Breaker.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Electro-magnetism for their operation.
15 feet off the ground.

45. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
Kilovolt ampere (KVA).
Electro-magnetism for their operation.
A step-up transformer.

46. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
12 to 15 times a minute.
277 volts.
15 feet off the ground.
Second-degree burn.

47. How do you change the direction of a 3-phase AC motor?
A device used to store electrical energy.
5:1.
Reverse any two-phase leads.
Hyperventilation.

48. High voltage is used to transmit power over long distances...
5:1.
Because less current flowing at high voltage causes less line loss per kilowatt.
480 volts.
Second-degree burn.

49. 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?
A step-up transformer.
75 turns.
Second-degree burn.
Circuit Breaker.

50. Which of the following does a squirrel cage induction motor have?
1 amp.
The capacitors should be discharged.
Stator windings.
100 turns.