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. 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.
They must be installed at least 7 feet above the ground.
At least two phases
Transformer

2. 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.
A grounding resistor.
5:1.
It provides good speed control.
Disconnect the frame-grounding conductor.

3. How should clothing be removed from a burn?
800 volts.
Cut around clothing that has adhered to the burned area.
A device used to store electrical energy.
The sum of the two capacitors.

4. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
100 turns.
The current will read zero.
They should be made by the same manufacturer.
1 amp.

5. Where should grounding resistors be located?
They should be made by the same manufacturer.
At the source transformer.
Clamp-on ammeter.
Carotid pulse - which is located in the neck next to the Adam's apple.

6. 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.
15 feet off the ground.
Draw less current.
Carotid pulse - which is located in the neck next to the Adam's apple.

7. The property of an electrical circuit that opposes any change in voltage is called...
Two speeds
Capacitance.
The current will read zero.
5:1

8. The standard frequency of alternating current used at a mine is...
60 Hertz
15 feet off the ground.
They must be installed at least 7 feet above the ground.
Transformers.

9. What should the duty rating of a grounding resistor be?
It provides good speed control.
Circuit Breaker.
Draw less current.
Continuous.

10. The secondary windings on a 10:1 step-down transformer will have a wire size...
Continuous.
Larger than that found in the primary winding.
7 -630 volts.
Transformer

11. To protect against over-current in a three-phase circuit over-current protection must be provided for...
60 Hertz
Shunted and taped
At least two phases
Current that changes constantly in magnitude and periodically in direction.

12. The purpose of a zig-zag transformer is to...
150 turns.
Derive a neutral for grounding purposes.
Lower current and higher voltage.
Alternating current.

13. Not true about AC power?
The motor rotation is reversed.
It provides good speed control.
Transformer
Larger than that found in the primary winding.

14. How do you change the direction of a 3-phase AC motor?
Check to make sure that the victim is not still in contact with the electricity.
25 feet.
Reverse any two-phase leads.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

15. The property of an electric circuit that opposes any change in current is called...
3 -979 Volts.
5:1.
Inductance.
200 volts AC.

16. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
The capacitors should be discharged.
Zero amps.
480 volts.
Alternating current.

17. Current in an AC circuit may be measured by...
Clamp-on ammeter.
100 volts.
Lower current and higher voltage.
Continuous.

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

19. Three-phase AC underground cables must be provided with overcurrent protection using a...
60 Hertz
75 turns.
Circuit Breaker.
Squirrel-cage rotor.

20. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
150 turns.
Isolation transformer.
75 turns.
The current will read zero.

21. The main function of CT's and PT's on a main substation is to...
Allow for metering voltage and Current.
5:1.
Clamp-on ammeter.
Because less current flowing at high voltage causes less line loss per kilowatt.

22. What type motor is a wound-rotor induction motor?
Potential transformer.
H terminals.
100 turns.
A.C.

23. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
Electro-magnetism for their operation.
480 volts.
Circuit Breaker.

24. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
Reverse its rotation.
No.6 AWG.
Shunted and taped

25. The standard frequency of power supplied by the power company is...
Two speeds
Reverse any two-phase leads.
60 cycles per second (60 Hertz).
A step-up transformer.

26. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
1 amp.
Squirrel-cage induction motor.
800 volts.

27. The primary function of a power transformer is to provide...
An electromagnet.
They must be installed at least 7 feet above the ground.
Full-load - three-phase voltage.
They should be made by the same manufacturer.

28. A transformer with 3000 turns in the primary winding has a primary voltage of 4 -800 volts and a secondary voltage of 240 volts. How many turns are in the secondary winding?
Inductance.
7 -630 volts.
At the source transformer.
150 turns.

29. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Allow for metering voltage and Current.
1 amp.
600 volts.
A grounding resistor.

30. Current that changes periodically in direction is...
Kilovolt ampere (KVA).
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Clamp-on ammeter.
Alternating current.

31. A wound-rotor induction motor has all the following EXCEPT...
Squirrel-cage rotor.
Hyperventilation.
The chest should rise or inflate.
Current changing constantly in magnitude and periodically in direction.

32. When not connected to a load - the secondary leads of a current transformer should be...
100 volts.
Shunted and taped
75 turns.
1 amp.

33. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Draw less current.
The current will read zero.
480 volts.

34. The transformer used only to measure voltage is a...
Current that changes constantly in magnitude and periodically in direction.
Reverse any two-phase leads.
Potential transformer.
At the source transformer.

35. What is a capacitor?
Carotid pulse - which is located in the neck next to the Adam's apple.
A device used to store electrical energy.
Current changing constantly in magnitude and periodically in direction.
Stator windings.

36. 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...
The chest should rise or inflate.
Current that changes constantly in magnitude and periodically in direction.
Grounded phase and ground fault devices were not operating.
Draw less current.

37. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Draw less current.
At least two phases

38. The primary leads of a single-phase transformer should be connected to the...
Larger than that found in the primary winding.
Full-load - three-phase voltage.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
H terminals.

39. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Four times less than that of the secondary.
Inductance.
Zero amps.
An electrical shock hazard may exist.

40. 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?
3 -979 Volts.
600 volts.
Squirrel-cage induction motor.
15 feet off the ground.

41. Define alternating current...
15 feet off the ground.
Squirrel-cage rotor.
Current that changes constantly in magnitude and periodically in direction.
Current changing constantly in magnitude and periodically in direction.

42. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
75 turns.
Squirrel-cage induction motor.
A step-up transformer.
800 volts.

43. 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 capacitors should be discharged.
Tied together
Squirrel-cage rotor.
277 volts.

44. A transformer with a 1:1 ratio is usually a (an)...
25 feet.
Isolation transformer.
7 -630 volts.
Grounded phase and ground fault devices were not operating.

45. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Two speeds
25 feet.
Because less current flowing at high voltage causes less line loss per kilowatt.

46. What is the danger when working around capacitors?
They must be installed at least 7 feet above the ground.
X.
An electrical shock hazard may exist.
It provides good speed control.

47. Compared to the secondary of a loaded - step-down transformer - the primary has...
Current changing constantly in magnitude and periodically in direction.
Full-load - three-phase voltage.
Lower current and higher voltage
75 turns.

48. What is the first step to be followed in aiding a victim of electrical shock?
Isolation transformer.
Check to make sure that the victim is not still in contact with the electricity.
At least two phases
Circuit Breaker.

49. Current transformers - or CT's - are used to...
25 feet.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Draw less current.
100 volts.

50. The size of a transformer is measured in...
Kilovolt ampere (KVA).
Short-circuited after power has been removed.
Reverse its rotation.
Lower current and higher voltage.