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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. 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.
277 volts.
7 -630 volts.
5:1
X.

2. The standard frequency of power supplied by the power company is...
Reverse any two-phase leads.
Electro-magnetism for their operation.
Squirrel-cage rotor.
60 cycles per second (60 Hertz).

3. 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...
7 -630 volts.
Stator windings.
Tied together
Provides single-phase power to smaller loads such as lights - heaters - etc.

4. Current transformers - or CT's - are used to...
Lower current and higher voltage
7 -630 volts.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Clamp-on ammeter.

5. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
Clamp-on ammeter.
60 cycles per second (60 Hertz).
800 volts.

6. 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.
100 turns.
Isolation transformer.
Squirrel-cage rotor.

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

8. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
H terminals.
Continuous.
Inductance.
Four times less than that of the secondary.

9. The primary function of a power transformer is to provide...
Transformers.
Larger than that found in the primary winding.
Full-load - three-phase voltage.
Capacitance.

10. 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...
Current changing constantly in magnitude and periodically in direction.
No.6 AWG.
100 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.

11. Three-phase AC underground cables must be provided with overcurrent protection using a...
Four times less than that of the secondary.
Circuit Breaker.
150 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.

12. Current that changes periodically in direction is...
The sum of the two capacitors.
Clamp-on ammeter.
Alternating current.
Transformer

13. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
It provides good speed control.
The current will read zero.
3 -979 Volts.

14. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Derive a neutral for grounding purposes.
Short-circuited after power has been removed.
75 turns.
Disconnect the frame-grounding conductor.

15. 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 rotor.
Lower current and higher voltage.
5:1.

16. Where should grounding resistors be located?
An electromagnet.
At the source transformer.
An electrical shock hazard may exist.
Squirrel-cage induction motor.

17. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
15 feet off the ground.
75 turns.
Derive a neutral for grounding purposes.

18. What should the duty rating of a grounding resistor be?
Inductance.
The current will read zero.
Nearly constant.
Continuous.

19. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
They should be made by the same manufacturer.
Carotid pulse - which is located in the neck next to the Adam's apple.
A.C.

20. The size of a transformer is measured in...
Zero amps.
Kilovolt ampere (KVA).
The capacitors should be discharged.
Check to make sure that the victim is not still in contact with the electricity.

21. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
800 volts.
7 -630 volts.
Potential transformer.

22. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Capacitance.
1 amp.
Provides single-phase power to smaller loads such as lights - heaters - etc.
480 volts.

23. What type motor is a wound-rotor induction motor?
Kilovolt ampere (KVA).
Draw less current.
Capacitance.
A.C.

24. 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...
Lower current and higher voltage
12 to 15 times a minute.
Hyperventilation.
Draw less current.

25. 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?
Draw less current.
800 volts.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Larger than that found in the primary winding.

26. The property of an electric circuit that opposes any change in current is called...
75 turns.
Inductance.
Draw less current.
No.6 AWG.

27. 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
800 volts.
Draw less current.
The sum of the two capacitors.

28. High voltage is used to transmit power over long distances...
12 to 15 times a minute.
A device used to store electrical energy.
At the source transformer.
Because less current flowing at high voltage causes less line loss per kilowatt.

29. What is the first step to be followed in aiding a victim of electrical shock?
Capacitance.
Squirrel-cage rotor.
Check to make sure that the victim is not still in contact with the electricity.
Cut around clothing that has adhered to the burned area.

30. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Kilovolt ampere (KVA).
25 feet.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
150 turns.

31. A solenoid coil is...
800 volts.
150 turns.
An electromagnet.
75 turns.

32. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
The chest should rise or inflate.
No.6 AWG.
Hyperventilation.
Lower current and higher voltage

33. The purpose of a zig-zag transformer is to...
Lower current and higher voltage
1 amp.
Derive a neutral for grounding purposes.
At least two phases

34. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
An electromagnet.
A.C.

35. Compared to the secondary of a loaded - step-down transformer - the primary has...
X.
7 -630 volts.
25 feet.
Lower current and higher voltage.

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

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37. What is a capacitor?
Kilovolt ampere (KVA).
Inductance.
A device used to store electrical energy.
Tied together

38. 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.
Alternating current.
5:1.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Derive a neutral for grounding purposes.

39. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
The sum of the two capacitors.
Capacitance.
100 volts.

40. What steps up or steps down AC voltage?
5:1
Transformer
Potential transformer.
Stator windings.

41. The transformer used only to measure voltage is a...
Reverse any two-phase leads.
Potential transformer.
100 volts.
5:1.

42. The property of an electrical circuit that opposes any change in voltage is called...
Continuous.
Carotid pulse - which is located in the neck next to the Adam's apple.
Capacitance.
100 volts.

43. The combined capacitance of two capacitors in parallel is...
800 volts.
Squirrel-cage rotor.
The sum of the two capacitors.
Draw less current.

44. 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.
Draw less current.
Clamp-on ammeter.
They must be installed at least 7 feet above the ground.

45. Not an acceptable method for the installations of surface transformers?
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
480 volts.
They must be installed at least 7 feet above the ground.
It provides good speed control.

46. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Circuit Breaker.
No.6 AWG.
Draw less current.

47. 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.
Two speeds
A step-up transformer.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

48. 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?
Cut around clothing that has adhered to the burned area.
Short-circuited after power has been removed.
Shunted and taped
100 turns.

49. Not a symptom of electrical shock?.
It provides good speed control.
Hyperventilation.
Current that changes constantly in magnitude and periodically in direction.
Transformer

50. When not connected to a load - the secondary leads of a current transformer should be...
Allow for metering voltage and Current.
Shunted and taped
They should be made by the same manufacturer.
Stator windings.