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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?
An electrical shock hazard may exist.
Hyperventilation.
It provides good speed control.
A step-up transformer.

2. The property of an electrical circuit that opposes any change in voltage is called...
Draw less current.
5:1
Because less current flowing at high voltage causes less line loss per kilowatt.
Capacitance.

3. 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...
It provides good speed control.
Draw less current.
Capacitance.
Hyperventilation.

4. What is the first step to be followed in aiding a victim of electrical shock?
100 volts.
800 volts.
Clamp-on ammeter.
Check to make sure that the victim is not still in contact with the electricity.

5. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The current will read zero.
A device used to store electrical energy.
Zero amps.
3 -979 Volts.

6. A control power transformer...
Derive a neutral for grounding purposes.
Draw less current.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Short-circuited after power has been removed.

7. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
The capacitors should be discharged.
Kilovolt ampere (KVA).
200 volts AC.

8. 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.
Four times less than that of the secondary.
H terminals.
5:1
Nearly constant.

9. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Lower current and higher voltage.
25 feet.
1 amp.
The chest should rise or inflate.

10. The transformer used only to measure voltage is a...
Transformers.
A device used to store electrical energy.
Potential transformer.
Cut around clothing that has adhered to the burned area.

11. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
The chest should rise or inflate.
Draw less current.
X.
Lower current and higher voltage

12. If any two-phase wires are reversed on a three-phase motor - the motor will...
Four times less than that of the secondary.
They should be made by the same manufacturer.
The motor rotation is reversed.
Reverse its rotation.

13. 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.
Second-degree burn.
A grounding resistor.
Full-load - three-phase voltage.

14. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
Provides single-phase power to smaller loads such as lights - heaters - etc.
An electrical shock hazard may exist.
A step-up transformer.

15. A wound-rotor induction motor has all the following EXCEPT...
Tied together
Check to make sure that the victim is not still in contact with the electricity.
480 volts.
Squirrel-cage rotor.

16. Current transformers - or CT's - are used to...
Alternating current.
Capacitance.
Stator windings.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

17. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Carotid pulse - which is located in the neck next to the Adam's apple.
Derive a neutral for grounding purposes.
A.C.
7 -630 volts.

18. What type motor is a wound-rotor induction motor?
A.C.
75 turns.
Check to make sure that the victim is not still in contact with the electricity.
Full-load - three-phase voltage.

19. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
60 cycles per second (60 Hertz).
Four times less than that of the secondary.
Reverse any two-phase leads.
Check to make sure that the victim is not still in contact with the electricity.

20. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
3 -979 Volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
Full-load - three-phase voltage.

21. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The motor rotation is reversed.
The sum of the two capacitors.
277 volts.
A step-up transformer.

22. When not connected to a load - the secondary leads of a current transformer should be...
At the source transformer.
Kilovolt ampere (KVA).
Shunted and taped
Zero amps.

23. AC voltage is raised or lowered by means of...
Transformers.
Squirrel-cage rotor.
Lower current and higher voltage
Alternating current.

24. Alternating current may be defined as...
Inductance.
A step-up transformer.
Current that changes constantly in magnitude and periodically in direction.
60 cycles per second (60 Hertz).

25. Compared to the secondary of a loaded - step-down transformer - the primary has...
Inductance.
A step-up transformer.
Lower current and higher voltage.
Short-circuited after power has been removed.

26. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Current changing constantly in magnitude and periodically in direction.
Cut around clothing that has adhered to the burned area.
They should be made by the same manufacturer.
Larger than that found in the primary winding.

27. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
480 volts.
It provides good speed control.
Shunted and taped

28. 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?
100 turns.
Full-load - three-phase voltage.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
75 turns.

29. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Grounded phase and ground fault devices were not operating.
Reverse any two-phase leads.
At least two phases
Current changing constantly in magnitude and periodically in direction.

30. 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...
Derive a neutral for grounding purposes.
Draw less current.
75 turns.
3 -979 Volts.

31. Current in an AC circuit may be measured by...
Lower current and higher voltage
Full-load - three-phase voltage.
An electrical shock hazard may exist.
Clamp-on ammeter.

32. Operating coils - motors - transformers - relays and solenoids depend upon...
Shunted and taped
The chest should rise or inflate.
Electro-magnetism for their operation.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

33. 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 step-up transformer.
Tied together
Shunted and taped
H terminals.

34. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Isolation transformer.
7 -630 volts.
Allow for metering voltage and Current.
Two speeds

35. What is the danger when working around capacitors?
5:1
Nearly constant.
An electrical shock hazard may exist.
Potential transformer.

36. The standard frequency of power supplied by the power company is...
Reverse its rotation.
60 cycles per second (60 Hertz).
Shunted and taped
At least two phases

37. The primary leads of a single-phase transformer should be connected to the...
Current changing constantly in magnitude and periodically in direction.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
H terminals.
Short-circuited after power has been removed.

38. A transformer with a 1:1 ratio is usually a (an)...
A grounding resistor.
Isolation transformer.
At the source transformer.
Transformers.

39. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
100 volts.
A.C.
A grounding resistor.
The capacitors should be discharged.

40. A burn causing a blister is classified as a...
75 turns.
Tied together
Second-degree burn.
H terminals.

41. 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.
Hyperventilation.
Four times less than that of the secondary.
Draw less current.

42. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Larger than that found in the primary winding.
A device used to store electrical energy.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

43. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Transformers.
800 volts.
Potential transformer.
2000 watts

44. 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?
Two speeds
A grounding resistor.
600 volts.
Short-circuited after power has been removed.

45. The size of a transformer is measured in...
Kilovolt ampere (KVA).
Nearly constant.
5:1
Current that changes constantly in magnitude and periodically in direction.

46. All transformers step voltage up or down by...
12 to 15 times a minute.
Shunted and taped
Inductance.
600 volts.

47. What steps up or steps down AC voltage?
Grounded phase and ground fault devices were not operating.
Transformer
Electro-magnetism for their operation.
25 feet.

48. Current that changes periodically in direction is...
Alternating current.
150 turns.
Isolation transformer.
An electrical shock hazard may exist.

49. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
No.6 AWG.
800 volts.
Zero amps.
1 amp.

50. What should the duty rating of a grounding resistor be?
Nearly constant.
The motor rotation is reversed.
Two speeds
Continuous.