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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. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
600 volts.
Lower current and higher voltage.
Clamp-on ammeter.

2. The purpose of a zig-zag transformer is to...
Squirrel-cage induction motor.
Disconnect the frame-grounding conductor.
Squirrel-cage rotor.
Derive a neutral for grounding purposes.

3. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Because less current flowing at high voltage causes less line loss per kilowatt.
Isolation transformer.
75 turns.

4. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Short-circuited after power has been removed.
Cut around clothing that has adhered to the burned area.
It provides good speed control.

5. Where should grounding resistors be located?
A grounding resistor.
At least two phases
A step-up transformer.
At the source transformer.

6. 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?
25 feet.
Isolation transformer.
200 volts AC.
75 turns.

7. If any two-phase wires are reversed on a three-phase motor - the motor will...
They should be made by the same manufacturer.
No.6 AWG.
Reverse its rotation.
H terminals.

8. Which of the following does a squirrel cage induction motor have?
150 turns.
Stator windings.
60 cycles per second (60 Hertz).
Full-load - three-phase voltage.

9. The size of a transformer is measured in...
Tied together
Full-load - three-phase voltage.
Squirrel-cage rotor.
Kilovolt ampere (KVA).

10. 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.
5:1
12 to 15 times a minute.
A.C.

11. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Kilovolt ampere (KVA).
7 -630 volts.
Draw less current.
1 amp.

12. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
At least two phases
Reverse its rotation.
The capacitors should be discharged.

13. AC voltage is raised or lowered by means of...
Inductance.
Transformers.
5:1
Full-load - three-phase voltage.

14. 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...
Cut around clothing that has adhered to the burned area.
H terminals.
Carotid pulse - which is located in the neck next to the Adam's apple.
Draw less current.

15. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The chest should rise or inflate.
Squirrel-cage induction motor.
The capacitors should be discharged.
Short-circuited after power has been removed.

16. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
60 Hertz
7 -630 volts.
The sum of the two capacitors.

17. 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...
25 feet.
5:1
Tied together
Alternating current.

18. Current in an AC circuit may be measured by...
75 turns.
Clamp-on ammeter.
Larger than that found in the primary winding.
200 volts AC.

19. Not true about AC power?
Circuit Breaker.
Larger than that found in the primary winding.
It provides good speed control.
480 volts.

20. How do you change the direction of a 3-phase AC motor?
Disconnect the frame-grounding conductor.
Inductance.
Reverse any two-phase leads.
Allow for metering voltage and Current.

21. The primary leads of a single-phase transformer should be connected to the...
Tied together
100 turns.
H terminals.
Grounded phase and ground fault devices were not operating.

22. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Two speeds
X.
Zero amps.
At the source transformer.

23. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
Lower current and higher voltage
Draw less current.
An electrical shock hazard may exist.

24. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
An electrical shock hazard may exist.
Transformer
Four times less than that of the secondary.
75 turns.

25. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Two speeds
5:1
An electrical shock hazard may exist.
480 volts.

26. What should the duty rating of a grounding resistor be?
Potential transformer.
Continuous.
Shunted and taped
The chest should rise or inflate.

27. 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?
Provides single-phase power to smaller loads such as lights - heaters - etc.
Carotid pulse - which is located in the neck next to the Adam's apple.
3 -979 Volts.
Second-degree burn.

28. Not an acceptable method for the installations of surface transformers?
100 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.
They must be installed at least 7 feet above the ground.
Nearly constant.

29. 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.
75 turns.
Transformer
The capacitors should be discharged.

30. A burn causing a blister is classified as a...
Because less current flowing at high voltage causes less line loss per kilowatt.
The current will read zero.
Draw less current.
Second-degree burn.

31. What is the danger when working around capacitors?
They must be installed at least 7 feet above the ground.
25 feet.
An electrical shock hazard may exist.
Allow for metering voltage and Current.

32. A solenoid coil is...
Alternating current.
At the source transformer.
An electromagnet.
Current changing constantly in magnitude and periodically in direction.

33. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
75 turns.
Hyperventilation.
Circuit Breaker.

34. 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.
Potential transformer.
7 -630 volts.
Cut around clothing that has adhered to the burned area.

35. The secondary windings on a 10:1 step-down transformer will have a wire size...
A device used to store electrical energy.
12 to 15 times a minute.
Larger than that found in the primary winding.
277 volts.

36. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
The current will read zero.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Shunted and taped
150 turns.

37. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
600 volts.
Two speeds
Reverse any two-phase leads.
5:1

38. The property of an electrical circuit that opposes any change in voltage is called...
Tied together
Derive a neutral for grounding purposes.
Capacitance.
60 cycles per second (60 Hertz).

39. 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.
The current will read zero.
100 volts.
5:1.
At least two phases

40. 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.
Squirrel-cage rotor.
Draw less current.
5:1
Current that changes constantly in magnitude and periodically in direction.

41. The standard frequency of power supplied by the power company is...
12 to 15 times a minute.
60 cycles per second (60 Hertz).
5:1.
No.6 AWG.

42. 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...
Draw less current.
Cut around clothing that has adhered to the burned area.
2000 watts
Isolation transformer.

43. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
Circuit Breaker.
5:1.
150 turns.

44. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
1 amp.
No.6 AWG.
15 feet off the ground.
The current will read zero.

45. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
60 cycles per second (60 Hertz).
200 volts AC.
They should be made by the same manufacturer.
X.

46. Three-phase AC underground cables must be provided with overcurrent protection using a...
Clamp-on ammeter.
An electrical shock hazard may exist.
Kilovolt ampere (KVA).
Circuit Breaker.

47. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Zero amps.
2000 watts
Potential transformer.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

48. What is a capacitor?
A device used to store electrical energy.
Stator windings.
480 volts.
The capacitors should be discharged.

49. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
The chest should rise or inflate.
12 to 15 times a minute.
Lower current and higher voltage.

50. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
A.C.
The sum of the two capacitors.
480 volts.