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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. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
Kilovolt ampere (KVA).
Shunted and taped
Capacitance.

2. The property of an electric circuit that opposes any change in current is called...
60 Hertz
75 turns.
Derive a neutral for grounding purposes.
Inductance.

3. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
An electromagnet.
Two speeds
Current changing constantly in magnitude and periodically in direction.
A step-up transformer.

4. All transformers step voltage up or down by...
At least two phases
They should be made by the same manufacturer.
Transformers.
Inductance.

5. Current in an AC circuit may be measured by...
150 turns.
Clamp-on ammeter.
480 volts.
Kilovolt ampere (KVA).

6. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
12 to 15 times a minute.
25 feet.
100 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

7. 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.
They must be installed at least 7 feet above the ground.
Capacitance.
Full-load - three-phase voltage.

8. How do you change the direction of a 3-phase AC motor?
60 Hertz
Clamp-on ammeter.
Continuous.
Reverse any two-phase leads.

9. A control power transformer...
Isolation transformer.
A.C.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Potential transformer.

10. Not true about AC power?
It provides good speed control.
Allow for metering voltage and Current.
Larger than that found in the primary winding.
Check to make sure that the victim is not still in contact with the electricity.

11. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Grounded phase and ground fault devices were not operating.
Short-circuited after power has been removed.
The sum of the two capacitors.
3 -979 Volts.

12. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Lower current and higher voltage
Squirrel-cage induction motor.
The sum of the two capacitors.

13. 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...
Continuous.
Draw less current.
They should be made by the same manufacturer.
Allow for metering voltage and Current.

14. A wound-rotor induction motor has all the following EXCEPT...
H terminals.
Squirrel-cage rotor.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Transformers.

15. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Grounded phase and ground fault devices were not operating.
Full-load - three-phase voltage.
2000 watts
12 to 15 times a minute.

16. The secondary windings on a 10:1 step-down transformer will have a wire size...
The chest should rise or inflate.
Larger than that found in the primary winding.
25 feet.
60 Hertz

17. The transformer used only to measure voltage is a...
Current changing constantly in magnitude and periodically in direction.
Potential transformer.
Capacitance.
60 cycles per second (60 Hertz).

18. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Derive a neutral for grounding purposes.
Isolation transformer.
No.6 AWG.
X.

19. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
600 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
The capacitors should be discharged.
15 feet off the ground.

20. 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...
Disconnect the frame-grounding conductor.
5:1.
100 volts.
Inductance.

21. The primary leads of a single-phase transformer should be connected to the...
H terminals.
Grounded phase and ground fault devices were not operating.
The capacitors should be discharged.
Clamp-on ammeter.

22. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
Check to make sure that the victim is not still in contact with the electricity.
Tied together
A grounding resistor.

23. 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?
Inductance.
200 volts AC.
An electromagnet.
75 turns.

24. 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.
600 volts.
At least two phases
277 volts.

25. A transformer with a 1:1 ratio is usually a (an)...
Lower current and higher voltage.
A.C.
Isolation transformer.
The chest should rise or inflate.

26. A burn causing a blister is classified as a...
Second-degree burn.
It provides good speed control.
Lower current and higher voltage.
An electromagnet.

27. The speed of an alternating current - squirrel-cage induction motor is...
Inductance.
Nearly constant.
Second-degree burn.
The sum of the two capacitors.

28. 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...
The sum of the two capacitors.
At least two phases
Isolation transformer.
Tied together

29. Three-phase AC underground cables must be provided with overcurrent protection using a...
Current changing constantly in magnitude and periodically in direction.
The capacitors should be discharged.
Circuit Breaker.
3 -979 Volts.

30. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Lower current and higher voltage.
480 volts.
15 feet off the ground.
Circuit Breaker.

31. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
At least two phases
3 -979 Volts.
No.6 AWG.
Tied together

32. High voltage is used to transmit power over long distances...
2000 watts
Carotid pulse - which is located in the neck next to the Adam's apple.
60 Hertz
Because less current flowing at high voltage causes less line loss per kilowatt.

33. AC voltage is raised or lowered by means of...
Hyperventilation.
Draw less current.
Transformers.
800 volts.

34. 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.
An electrical shock hazard may exist.
480 volts.
3 -979 Volts.

35. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Capacitance.
Four times less than that of the secondary.
Inductance.
The chest should rise or inflate.

36. What is the first step to be followed in aiding a victim of electrical shock?
12 to 15 times a minute.
The motor rotation is reversed.
Check to make sure that the victim is not still in contact with the electricity.
Hyperventilation.

37. Compared to the secondary of a loaded - step-down transformer - the primary has...
Transformer
Because less current flowing at high voltage causes less line loss per kilowatt.
A step-up transformer.
Lower current and higher voltage.

38. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
The chest should rise or inflate.
480 volts.
Inductance.
Zero amps.

39. 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?
Current changing constantly in magnitude and periodically in direction.
Second-degree burn.
800 volts.
Zero amps.

40. What should the duty rating of a grounding resistor be?
100 turns.
They must be installed at least 7 feet above the ground.
Lower current and higher voltage.
Continuous.

41. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Derive a neutral for grounding purposes.
At the source transformer.
12 to 15 times a minute.
The motor rotation is reversed.

42. The combined capacitance of two capacitors in parallel is...
5:1
2000 watts
The sum of the two capacitors.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

43. The main function of CT's and PT's on a main substation is to...
75 turns.
An electromagnet.
15 feet off the ground.
Allow for metering voltage and Current.

44. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
277 volts.
100 volts.
They should be made by the same manufacturer.

45. A solenoid coil is...
Circuit Breaker.
An electromagnet.
5:1
Lower current and higher voltage.

46. Compared to the secondary of a loaded - step-down transformer - the primary has...
Full-load - three-phase voltage.
Potential transformer.
Lower current and higher voltage
Squirrel-cage induction motor.

47. 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?
Current changing constantly in magnitude and periodically in direction.
Inductance.
15 feet off the ground.
75 turns.

48. The purpose of a zig-zag transformer is to...
They should be made by the same manufacturer.
Tied together
Derive a neutral for grounding purposes.
An electromagnet.

49. 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?
The sum of the two capacitors.
Larger than that found in the primary winding.
75 turns.
They must be installed at least 7 feet above the ground.

50. What is the danger when working around capacitors?
75 turns.
An electrical shock hazard may exist.
Inductance.
The motor rotation is reversed.