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Test your basic knowledge |

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 main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
The chest should rise or inflate.
150 turns.
3 -979 Volts.

2. 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?
5:1
Four times less than that of the secondary.
Reverse its rotation.
3 -979 Volts.

3. Not true about AC power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
It provides good speed control.
Potential transformer.
Isolation transformer.

4. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
A grounding resistor.
5:1.
H terminals.

5. 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.
Alternating current.
Kilovolt ampere (KVA).
Electro-magnetism for their operation.

6. Where should grounding resistors be located?
7 -630 volts.
At the source transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Full-load - three-phase voltage.

7. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Zero amps.
Tied together
The capacitors should be discharged.
They must be installed at least 7 feet above the ground.

8. Not a symptom of electrical shock?.
Tied together
Capacitance.
Hyperventilation.
Draw less current.

9. A solenoid coil is...
No.6 AWG.
An electromagnet.
At least two phases
Transformers.

10. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
The sum of the two capacitors.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Cut around clothing that has adhered to the burned area.
25 feet.

11. AC voltage is raised or lowered by means of...
Current that changes constantly in magnitude and periodically in direction.
Draw less current.
Transformers.
Reverse any two-phase leads.

12. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Current that changes constantly in magnitude and periodically in direction.
Disconnect the frame-grounding conductor.
Inductance.
X.

13. 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...
Nearly constant.
Inductance.
Draw less current.
Continuous.

14. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
Squirrel-cage induction motor.
They must be installed at least 7 feet above the ground.
It provides good speed control.

15. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Disconnect the frame-grounding conductor.
Two speeds
Tied together
Cut around clothing that has adhered to the burned area.

16. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Provides single-phase power to smaller loads such as lights - heaters - etc.
At least two phases
Stator windings.
Capacitance.

17. The purpose of a zig-zag transformer is to...
Allow for metering voltage and Current.
A step-up transformer.
Full-load - three-phase voltage.
Derive a neutral for grounding purposes.

18. All transformers step voltage up or down by...
Inductance.
The current will read zero.
277 volts.
100 volts.

19. The primary leads of a single-phase transformer should be connected to the...
Capacitance.
H terminals.
277 volts.
Squirrel-cage rotor.

20. The property of an electric circuit that opposes any change in current is called...
60 cycles per second (60 Hertz).
Squirrel-cage induction motor.
Inductance.
480 volts.

21. High voltage is used to transmit power over long distances...
At the source transformer.
At least two phases
Because less current flowing at high voltage causes less line loss per kilowatt.
The sum of the two capacitors.

22. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Full-load - three-phase voltage.
Transformers.
1 amp.
Current that changes constantly in magnitude and periodically in direction.

23. The primary function of a power transformer is to provide...
277 volts.
200 volts AC.
Full-load - three-phase voltage.
2000 watts

24. A burn causing a blister is classified as a...
Second-degree burn.
H terminals.
A.C.
A grounding resistor.

25. The size of a transformer is measured in...
Kilovolt ampere (KVA).
A device used to store electrical energy.
2000 watts
Full-load - three-phase voltage.

26. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
3 -979 Volts.
Inductance.
Zero amps.
No.6 AWG.

27. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Isolation transformer.
Clamp-on ammeter.
Two speeds

28. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
Cut around clothing that has adhered to the burned area.
Draw less current.
Reverse any two-phase leads.

29. At what rate should mouth-to-mouth resuscitation be applied?
Inductance.
Because less current flowing at high voltage causes less line loss per kilowatt.
12 to 15 times a minute.
60 cycles per second (60 Hertz).

30. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Transformer
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
They should be made by the same manufacturer.
At least two phases

31. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A step-up transformer.
Disconnect the frame-grounding conductor.
100 volts.
Kilovolt ampere (KVA).

32. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
H terminals.
An electrical shock hazard may exist.
The chest should rise or inflate.
Draw less current.

33. Not an acceptable method for the installations of surface transformers?
They must be installed at least 7 feet above the ground.
75 turns.
Isolation transformer.
A device used to store electrical energy.

34. 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.
It provides good speed control.
Continuous.
Provides single-phase power to smaller loads such as lights - heaters - etc.

35. 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.
200 volts AC.
1 amp.

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

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.
Potential transformer.
Squirrel-cage rotor.
Reverse its rotation.

38. Three-phase AC underground cables must be provided with overcurrent protection using a...
They should be made by the same manufacturer.
Inductance.
Circuit Breaker.
Two speeds

39. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Lower current and higher voltage
A grounding resistor.
Four times less than that of the secondary.
The motor rotation is reversed.

40. How do you change the direction of a 3-phase AC motor?
Electro-magnetism for their operation.
Reverse any two-phase leads.
They should be made by the same manufacturer.
Lower current and higher voltage

41. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Because less current flowing at high voltage causes less line loss per kilowatt.
Inductance.
Lower current and higher voltage.
Short-circuited after power has been removed.

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.
Transformers.
Isolation transformer.
Circuit Breaker.

43. What is the first step to be followed in aiding a victim of electrical shock?
Check to make sure that the victim is not still in contact with the electricity.
Derive a neutral for grounding purposes.
Carotid pulse - which is located in the neck next to the Adam's apple.
Short-circuited after power has been removed.

44. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
Stator windings.
H terminals.
3 -979 Volts.

45. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
Stator windings.
Check to make sure that the victim is not still in contact with the electricity.
Full-load - three-phase voltage.

46. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
60 Hertz
Reverse its rotation.
Capacitance.

47. 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?
Four times less than that of the secondary.
100 turns.
Capacitance.
A grounding resistor.

48. 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.
480 volts.
Nearly constant.
They must be installed at least 7 feet above the ground.

49. What is a capacitor?
60 Hertz
Tied together
A device used to store electrical energy.
The motor rotation is reversed.

50. The transformer used only to measure voltage is a...
150 turns.
Current changing constantly in magnitude and periodically in direction.
Potential transformer.
60 Hertz