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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 solenoid coil is...
Tied together
The capacitors should be discharged.
Alternating current.
An electromagnet.

2. Compared to the secondary of a loaded - step-down transformer - the primary has...
Circuit Breaker.
60 Hertz
100 turns.
Lower current and higher voltage

3. Not true about AC power?
It provides good speed control.
The sum of the two capacitors.
7 -630 volts.
A.C.

4. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Full-load - three-phase voltage.
Grounded phase and ground fault devices were not operating.
277 volts.
Current that changes constantly in magnitude and periodically in direction.

5. The speed of an alternating current - squirrel-cage induction motor is...
Zero amps.
Stator windings.
Nearly constant.
H terminals.

6. Current that changes periodically in direction is...
Short-circuited after power has been removed.
7 -630 volts.
Lower current and higher voltage
Alternating current.

7. 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?
Transformer
60 Hertz
100 turns.
277 volts.

8. 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.
Hyperventilation.
At least two phases
2000 watts

9. Current in an AC circuit may be measured by...
800 volts.
Clamp-on ammeter.
Reverse its rotation.
Transformer

10. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
Hyperventilation.
Disconnect the frame-grounding conductor.
Transformers.

11. The secondary windings on a 10:1 step-down transformer will have a wire size...
H terminals.
Carotid pulse - which is located in the neck next to the Adam's apple.
Larger than that found in the primary winding.
A step-up transformer.

12. 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...
Stator windings.
Derive a neutral for grounding purposes.
Circuit Breaker.
Tied together

13. What should the duty rating of a grounding resistor be?
Continuous.
Capacitance.
100 volts.
Clamp-on ammeter.

14. 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?
The capacitors should be discharged.
Draw less current.
Kilovolt ampere (KVA).
800 volts.

15. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Short-circuited after power has been removed.
The chest should rise or inflate.
600 volts.
An electromagnet.

16. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Inductance.
200 volts AC.
2000 watts
100 turns.

17. 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?
25 feet.
600 volts.
They must be installed at least 7 feet above the ground.
Draw less current.

18. All transformers step voltage up or down by...
Stator windings.
The motor rotation is reversed.
Shunted and taped
Inductance.

19. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Check to make sure that the victim is not still in contact with the electricity.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
A device used to store electrical energy.
Tied together

20. 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.
A.C.
Draw less current.
They should be made by the same manufacturer.

21. What is the danger when working around capacitors?
An electrical shock hazard may exist.
The sum of the two capacitors.
75 turns.
Nearly constant.

22. The primary leads of a single-phase transformer should be connected to the...
H terminals.
Tied together
The current will read zero.
At the source transformer.

23. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
At the source transformer.
Tied together
The motor rotation is reversed.
No.6 AWG.

24. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
A.C.
75 turns.
150 turns.
Two speeds

25. 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...
800 volts.
100 volts.
H terminals.
Circuit Breaker.

26. 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?
3 -979 Volts.
Tied together
Nearly constant.
Squirrel-cage induction motor.

27. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Current that changes constantly in magnitude and periodically in direction.
Electro-magnetism for their operation.
Lower current and higher voltage.
No.6 AWG.

28. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
100 volts.
Hyperventilation.
Disconnect the frame-grounding conductor.
An electrical shock hazard may exist.

29. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
600 volts.
Zero amps.
X.
2000 watts

30. Alternating current may be defined as...
Clamp-on ammeter.
Capacitance.
Current that changes constantly in magnitude and periodically in direction.
Grounded phase and ground fault devices were not operating.

31. If any two-phase wires are reversed on a three-phase motor - the motor will...
Clamp-on ammeter.
800 volts.
Reverse any two-phase leads.
Reverse its rotation.

32. What type motor is a wound-rotor induction motor?
75 turns.
A.C.
800 volts.
5:1

33. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Draw less current.
5:1.
Short-circuited after power has been removed.

34. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
They should be made by the same manufacturer.
A step-up transformer.
The capacitors should be discharged.
Transformer

35. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
They should be made by the same manufacturer.
Transformers.
25 feet.
At least two phases

36. Not an acceptable method for the installations of surface transformers?
5:1.
A step-up transformer.
75 turns.
They must be installed at least 7 feet above the ground.

37. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Draw less current.
They must be installed at least 7 feet above the ground.
480 volts.

38. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
No.6 AWG.
Lower current and higher voltage
A.C.

39. The main function of CT's and PT's on a main substation is to...
Capacitance.
Allow for metering voltage and Current.
150 turns.
Reverse its rotation.

40. 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.
Squirrel-cage induction motor.
Full-load - three-phase voltage.
An electromagnet.

41. The transformer used only to measure voltage is a...
60 Hertz
Potential transformer.
Stator windings.
Two speeds

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.
600 volts.
100 turns.
Shunted and taped

43. 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.
Because less current flowing at high voltage causes less line loss per kilowatt.
Allow for metering voltage and Current.
5:1
A step-up transformer.

44. At what rate should mouth-to-mouth resuscitation be applied?
5:1.
12 to 15 times a minute.
Derive a neutral for grounding purposes.
Reverse any two-phase leads.

45. What steps up or steps down AC voltage?
Reverse any two-phase leads.
No.6 AWG.
Transformer
The chest should rise or inflate.

46. Where should grounding resistors be located?
Two speeds
Nearly constant.
Disconnect the frame-grounding conductor.
At the source transformer.

47. Define alternating current...
25 feet.
Current changing constantly in magnitude and periodically in direction.
No.6 AWG.
A grounding resistor.

48. Which of the following does a squirrel cage induction motor have?
Second-degree burn.
Squirrel-cage rotor.
Stator windings.
H terminals.

49. 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
3 -979 Volts.
Transformer

50. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
The chest should rise or inflate.
The current will read zero.
Reverse any two-phase leads.
Tied together