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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. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Four times less than that of the secondary.
The motor rotation is reversed.
At the source transformer.
A step-up transformer.

2. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Hyperventilation.
7 -630 volts.
12 to 15 times a minute.
Reverse its rotation.

3. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Shunted and taped
The current will read zero.
5:1
Alternating current.

4. 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...
Reverse its rotation.
An electrical shock hazard may exist.
Tied together
Nearly constant.

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.
Two speeds
Cut around clothing that has adhered to the burned area.
Potential transformer.

6. If any two-phase wires are reversed on a three-phase motor - the motor will...
Four times less than that of the secondary.
Lower current and higher voltage.
X.
Reverse its rotation.

7. 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?
Reverse its rotation.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
480 volts.
75 turns.

8. Three-phase AC underground cables must be provided with overcurrent protection using a...
Nearly constant.
Shunted and taped
600 volts.
Circuit Breaker.

9. 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.
A grounding resistor.
The motor rotation is reversed.
5:1
Clamp-on ammeter.

10. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A grounding resistor.
The chest should rise or inflate.
Stator windings.
A step-up transformer.

11. A wound-rotor induction motor has all the following EXCEPT...
7 -630 volts.
Squirrel-cage rotor.
Electro-magnetism for their operation.
Continuous.

12. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Two speeds
Carotid pulse - which is located in the neck next to the Adam's apple.
277 volts.
No.6 AWG.

13. A burn causing a blister is classified as a...
Second-degree burn.
Circuit Breaker.
Grounded phase and ground fault devices were not operating.
480 volts.

14. 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...
100 volts.
Short-circuited after power has been removed.
A grounding resistor.
Isolation transformer.

15. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Zero amps.
The capacitors should be discharged.
Disconnect the frame-grounding conductor.
15 feet off the ground.

16. Which of the following does a squirrel cage induction motor have?
Stator windings.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Kilovolt ampere (KVA).
Full-load - three-phase voltage.

17. The purpose of a zig-zag transformer is to...
A device used to store electrical energy.
60 cycles per second (60 Hertz).
Lower current and higher voltage.
Derive a neutral for grounding purposes.

18. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
An electromagnet.
15 feet off the ground.
Cut around clothing that has adhered to the burned area.

19. The speed of an alternating current - squirrel-cage induction motor is...
75 turns.
Nearly constant.
Inductance.
Hyperventilation.

20. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Allow for metering voltage and Current.
Squirrel-cage rotor.
Two speeds

21. What is the danger when working around capacitors?
An electrical shock hazard may exist.
Cut around clothing that has adhered to the burned area.
Tied together
At the source transformer.

22. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
480 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Grounded phase and ground fault devices were not operating.
Current that changes constantly in magnitude and periodically in direction.

23. A control power transformer...
Current that changes constantly in magnitude and periodically in direction.
Lower current and higher voltage
Provides single-phase power to smaller loads such as lights - heaters - etc.
A step-up transformer.

24. 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?
75 turns.
No.6 AWG.
150 turns.
Disconnect the frame-grounding conductor.

25. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
25 feet.
Second-degree burn.
Derive a neutral for grounding purposes.

26. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
A step-up transformer.
5:1.
100 volts.

27. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
Hyperventilation.
Current that changes constantly in magnitude and periodically in direction.
75 turns.

28. Operating coils - motors - transformers - relays and solenoids depend upon...
The sum of the two capacitors.
Electro-magnetism for their operation.
800 volts.
Squirrel-cage induction motor.

29. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
H terminals.
At the source transformer.
3 -979 Volts.

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

31. Compared to the secondary of a loaded - step-down transformer - the primary has...
Disconnect the frame-grounding conductor.
Lower current and higher voltage.
2000 watts
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

32. 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.
Carotid pulse - which is located in the neck next to the Adam's apple.
Lower current and higher voltage
Inductance.

33. Not a symptom of electrical shock?.
A step-up transformer.
Hyperventilation.
Allow for metering voltage and Current.
60 Hertz

34. Not true about AC power?
An electrical shock hazard may exist.
It provides good speed control.
Second-degree burn.
Potential transformer.

35. The transformer used only to measure voltage is a...
Potential transformer.
Four times less than that of the secondary.
Full-load - three-phase voltage.
Circuit Breaker.

36. The combined capacitance of two capacitors in parallel is...
Lower current and higher voltage
Inductance.
The sum of the two capacitors.
At the source transformer.

37. 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?
100 turns.
3 -979 Volts.
60 cycles per second (60 Hertz).
Check to make sure that the victim is not still in contact with the electricity.

38. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
480 volts.
They should be made by the same manufacturer.
Allow for metering voltage and Current.

39. A transformer with a 1:1 ratio is usually a (an)...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Grounded phase and ground fault devices were not operating.
Full-load - three-phase voltage.
Isolation transformer.

40. Define alternating current...
Larger than that found in the primary winding.
Inductance.
Current changing constantly in magnitude and periodically in direction.
At least two phases

41. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
1 amp.
5:1
Clamp-on ammeter.

42. A solenoid coil is...
An electromagnet.
Disconnect the frame-grounding conductor.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
They must be installed at least 7 feet above the ground.

43. 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?
75 turns.
The sum of the two capacitors.
5:1.
No.6 AWG.

44. 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.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The capacitors should be discharged.
1 amp.

45. 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
Current that changes constantly in magnitude and periodically in direction.
Squirrel-cage induction motor.
25 feet.

46. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
The sum of the two capacitors.
Grounded phase and ground fault devices were not operating.
A step-up transformer.
Transformer

47. 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.
Lower current and higher voltage.
7 -630 volts.
150 turns.

48. 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
Transformers.
Carotid pulse - which is located in the neck next to the Adam's apple.
Cut around clothing that has adhered to the burned area.

49. 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.
Carotid pulse - which is located in the neck next to the Adam's apple.
Full-load - three-phase voltage.
An electrical shock hazard may exist.

50. To protect against over-current in a three-phase circuit over-current protection must be provided for...
15 feet off the ground.
At least two phases
Because less current flowing at high voltage causes less line loss per kilowatt.
Reverse its rotation.