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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. 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?
Because less current flowing at high voltage causes less line loss per kilowatt.
150 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.
A.C.

2. The standard frequency of power supplied by the power company is...
The motor rotation is reversed.
Provides single-phase power to smaller loads such as lights - heaters - etc.
H terminals.
60 cycles per second (60 Hertz).

3. The purpose of a zig-zag transformer is to...
Clamp-on ammeter.
100 volts.
Derive a neutral for grounding purposes.
5:1.

4. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Capacitance.
Reverse any two-phase leads.
A step-up transformer.

5. The primary function of a power transformer is to provide...
600 volts.
Full-load - three-phase voltage.
Shunted and taped
Continuous.

6. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Draw less current.
Inductance.
480 volts.

7. The standard frequency of alternating current used at a mine is...
60 Hertz
12 to 15 times a minute.
Current that changes constantly in magnitude and periodically in direction.
Potential transformer.

8. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Squirrel-cage induction motor.
Lower current and higher voltage
The motor rotation is reversed.
Tied together

9. Current that changes periodically in direction is...
Alternating current.
Stator windings.
Clamp-on ammeter.
The chest should rise or inflate.

10. At what rate should mouth-to-mouth resuscitation be applied?
25 feet.
A step-up transformer.
12 to 15 times a minute.
An electromagnet.

11. 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?
Isolation transformer.
It provides good speed control.
800 volts.
Potential transformer.

12. Compared to the secondary of a loaded - step-down transformer - the primary has...
At least two phases
Lower current and higher voltage
Check to make sure that the victim is not still in contact with the electricity.
Alternating current.

13. 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.
At least two phases
800 volts.
H terminals.

14. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Disconnect the frame-grounding conductor.
800 volts.
Tied together
1 amp.

15. A burn causing a blister is classified as a...
The motor rotation is reversed.
Second-degree burn.
Tied together
Derive a neutral for grounding purposes.

16. Current transformers - or CT's - are used to...
Allow for metering voltage and Current.
An electromagnet.
The motor rotation is reversed.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

17. The size of a transformer is measured in...
An electromagnet.
Kilovolt ampere (KVA).
Tied together
Disconnect the frame-grounding conductor.

18. All transformers step voltage up or down by...
Circuit Breaker.
Inductance.
2000 watts
25 feet.

19. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
Derive a neutral for grounding purposes.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
200 volts AC.

20. What is the first step to be followed in aiding a victim of electrical shock?
Draw less current.
100 volts.
60 Hertz
Check to make sure that the victim is not still in contact with the electricity.

21. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
277 volts.
Grounded phase and ground fault devices were not operating.
100 turns.
600 volts.

22. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Four times less than that of the secondary.
Derive a neutral for grounding purposes.
150 turns.

23. Not true about AC power?
It provides good speed control.
Second-degree burn.
Stator windings.
The sum of the two capacitors.

24. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Tied together
Carotid pulse - which is located in the neck next to the Adam's apple.
The motor rotation is reversed.
25 feet.

25. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Allow for metering voltage and Current.
Because less current flowing at high voltage causes less line loss per kilowatt.
No.6 AWG.
Zero amps.

26. 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.
Two speeds
Lower current and higher voltage
75 turns.
5:1

27. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
Lower current and higher voltage
A.C.
The chest should rise or inflate.

28. The primary leads of a single-phase transformer should be connected to the...
H terminals.
Inductance.
Provides single-phase power to smaller loads such as lights - heaters - etc.
5:1.

29. Which of the following does a squirrel cage induction motor have?
The sum of the two capacitors.
Stator windings.
75 turns.
Lower current and higher voltage.

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...
Draw less current.
Hyperventilation.
A step-up transformer.
A grounding resistor.

31. 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?
Larger than that found in the primary winding.
200 volts AC.
75 turns.
Lower current and higher voltage

32. A solenoid coil is...
At the source transformer.
A step-up transformer.
An electromagnet.
100 turns.

33. 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...
Clamp-on ammeter.
Full-load - three-phase voltage.
2000 watts
Draw less current.

34. The property of an electrical circuit that opposes any change in voltage is called...
Clamp-on ammeter.
60 Hertz
They should be made by the same manufacturer.
Capacitance.

35. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Larger than that found in the primary winding.
They should be made by the same manufacturer.
Carotid pulse - which is located in the neck next to the Adam's apple.
100 turns.

36. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Short-circuited after power has been removed.
277 volts.
3 -979 Volts.
Full-load - three-phase voltage.

37. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
15 feet off the ground.
Nearly constant.
Squirrel-cage induction motor.
2000 watts

38. The secondary windings on a 10:1 step-down transformer will have a wire size...
A.C.
Zero amps.
Allow for metering voltage and Current.
Larger than that found in the primary winding.

39. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
Tied together
A step-up transformer.
3 -979 Volts.

40. 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?
75 turns.
12 to 15 times a minute.
Squirrel-cage induction motor.
Draw less current.

41. How should clothing be removed from a burn?
Isolation transformer.
Draw less current.
A.C.
Cut around clothing that has adhered to the burned area.

42. A transformer with a 1:1 ratio is usually a (an)...
Lower current and higher voltage.
600 volts.
Lower current and higher voltage
Isolation transformer.

43. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
15 feet off the ground.
75 turns.
Grounded phase and ground fault devices were not operating.
7 -630 volts.

44. 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...
Continuous.
Hyperventilation.
It provides good speed control.
Tied together

45. Current in an AC circuit may be measured by...
60 Hertz
Clamp-on ammeter.
Nearly constant.
Kilovolt ampere (KVA).

46. What is the danger when working around capacitors?
60 cycles per second (60 Hertz).
Four times less than that of the secondary.
An electrical shock hazard may exist.
60 Hertz

47. AC voltage is raised or lowered by means of...
Transformers.
The motor rotation is reversed.
It provides good speed control.
A step-up transformer.

48. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Kilovolt ampere (KVA).
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The chest should rise or inflate.
Reverse any two-phase leads.

49. 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.
Allow for metering voltage and Current.
Alternating current.
Check to make sure that the victim is not still in contact with the electricity.

50. Define alternating current...
Circuit Breaker.
Current changing constantly in magnitude and periodically in direction.
At least two phases
15 feet off the ground.