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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. Not true about AC power?
It provides good speed control.
Continuous.
Capacitance.
200 volts AC.

2. A transformer with a 1:1 ratio is usually a (an)...
Four times less than that of the secondary.
Because less current flowing at high voltage causes less line loss per kilowatt.
Isolation transformer.
Shunted and taped

3. The purpose of a zig-zag transformer is to...
Carotid pulse - which is located in the neck next to the Adam's apple.
No.6 AWG.
Isolation transformer.
Derive a neutral for grounding purposes.

4. The combined capacitance of two capacitors in parallel is...
H terminals.
The sum of the two capacitors.
Grounded phase and ground fault devices were not operating.
Tied together

5. 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...
25 feet.
Draw less current.
Capacitance.
The capacitors should be discharged.

6. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
The sum of the two capacitors.
Inductance.
Four times less than that of the secondary.
Two speeds

7. AC voltage is raised or lowered by means of...
800 volts.
Hyperventilation.
The sum of the two capacitors.
Transformers.

8. How should clothing be removed from a burn?
Reverse any two-phase leads.
Current changing constantly in magnitude and periodically in direction.
60 Hertz
Cut around clothing that has adhered to the burned area.

9. Define alternating current...
100 volts.
Current changing constantly in magnitude and periodically in direction.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Draw less current.

10. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
5:1
Lower current and higher voltage
Allow for metering voltage and Current.
Grounded phase and ground fault devices were not operating.

11. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Nearly constant.
They must be installed at least 7 feet above the ground.
No.6 AWG.

12. What is the first step to be followed in aiding a victim of electrical shock?
75 turns.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Check to make sure that the victim is not still in contact with the electricity.
X.

13. The primary leads of a single-phase transformer should be connected to the...
7 -630 volts.
A device used to store electrical energy.
Lower current and higher voltage.
H terminals.

14. Where should grounding resistors be located?
Hyperventilation.
At the source transformer.
200 volts AC.
Alternating current.

15. Compared to the secondary of a loaded - step-down transformer - the primary has...
Four times less than that of the secondary.
Lower current and higher voltage.
A grounding resistor.
The sum of the two capacitors.

16. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Short-circuited after power has been removed.
Disconnect the frame-grounding conductor.
An electrical shock hazard may exist.
Full-load - three-phase voltage.

17. Three-phase AC underground cables must be provided with overcurrent protection using a...
3 -979 Volts.
Circuit Breaker.
Inductance.
Kilovolt ampere (KVA).

18. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Full-load - three-phase voltage.
Isolation transformer.
Zero amps.
The motor rotation is reversed.

19. How do you change the direction of a 3-phase AC motor?
Provides single-phase power to smaller loads such as lights - heaters - etc.
X.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Reverse any two-phase leads.

20. The primary function of a power transformer is to provide...
Transformer
Circuit Breaker.
A device used to store electrical energy.
Full-load - three-phase voltage.

21. The property of an electric circuit that opposes any change in current is called...
Inductance.
Circuit Breaker.
An electromagnet.
Squirrel-cage induction motor.

22. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
5:1
Carotid pulse - which is located in the neck next to the Adam's apple.
12 to 15 times a minute.

23. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Alternating current.
Derive a neutral for grounding purposes.
75 turns.
25 feet.

24. Current in an AC circuit may be measured by...
100 turns.
3 -979 Volts.
Clamp-on ammeter.
Transformers.

25. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Short-circuited after power has been removed.
Draw less current.
Clamp-on ammeter.
An electromagnet.

26. A control power transformer...
Disconnect the frame-grounding conductor.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Two speeds
Derive a neutral for grounding purposes.

27. A burn causing a blister is classified as a...
Second-degree burn.
277 volts.
Reverse any two-phase leads.
Capacitance.

28. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
The current will read zero.
Hyperventilation.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
1 amp.

29. The transformer used only to measure voltage is a...
Because less current flowing at high voltage causes less line loss per kilowatt.
Potential transformer.
Larger than that found in the primary winding.
800 volts.

30. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
12 to 15 times a minute.
Inductance.
No.6 AWG.

31. The size of a transformer is measured in...
60 Hertz
Capacitance.
Shunted and taped
Kilovolt ampere (KVA).

32. What type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
Carotid pulse - which is located in the neck next to the Adam's apple.
Provides single-phase power to smaller loads such as lights - heaters - etc.
A step-up transformer.

33. Which of the following does a squirrel cage induction motor have?
Transformer
A grounding resistor.
Stator windings.
Two speeds

34. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Disconnect the frame-grounding conductor.
No.6 AWG.
The current will read zero.
Stator windings.

35. Not an acceptable method for the installations of surface transformers?
The current will read zero.
A.C.
They must be installed at least 7 feet above the ground.
A device used to store electrical energy.

36. 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?
3 -979 Volts.
7 -630 volts.
Squirrel-cage induction motor.
A.C.

37. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Alternating current.
Zero amps.
277 volts.
They should be made by the same manufacturer.

38. 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.
H terminals.
Clamp-on ammeter.
Derive a neutral for grounding purposes.

39. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Alternating current.
No.6 AWG.
7 -630 volts.
Stator windings.

40. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Shunted and taped
A grounding resistor.
The motor rotation is reversed.
Derive a neutral for grounding purposes.

41. All transformers step voltage up or down by...
X.
7 -630 volts.
Electro-magnetism for their operation.
Inductance.

42. 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.
Electro-magnetism for their operation.
60 Hertz
Full-load - three-phase voltage.

43. What steps up or steps down AC voltage?
Squirrel-cage rotor.
Because less current flowing at high voltage causes less line loss per kilowatt.
Current that changes constantly in magnitude and periodically in direction.
Transformer

44. 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?
100 turns.
Larger than that found in the primary winding.
3 -979 Volts.
Kilovolt ampere (KVA).

45. Current transformers - or CT's - are used to...
Because less current flowing at high voltage causes less line loss per kilowatt.
Allow for metering voltage and Current.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Nearly constant.

46. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
5:1.
Because less current flowing at high voltage causes less line loss per kilowatt.
Disconnect the frame-grounding conductor.

47. 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?
At least two phases
75 turns.
Hyperventilation.
The capacitors should be discharged.

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

49. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The current will read zero.
The chest should rise or inflate.
Squirrel-cage rotor.
Second-degree burn.

50. 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...
3 -979 Volts.
Lower current and higher voltage
Continuous.
100 volts.