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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. 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.
Alternating current.
75 turns.
200 volts AC.

2. 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?
Transformer
They must be installed at least 7 feet above the ground.
800 volts.
Full-load - three-phase voltage.

3. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
100 turns.
Two speeds
A device used to store electrical energy.

4. 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...
Lower current and higher voltage
Draw less current.
Reverse its rotation.
Continuous.

5. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
12 to 15 times a minute.
Four times less than that of the secondary.
At the source transformer.
Transformer

6. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
The chest should rise or inflate.
277 volts.
An electrical shock hazard may exist.

7. The primary leads of a single-phase transformer should be connected to the...
H terminals.
The sum of the two capacitors.
Derive a neutral for grounding purposes.
200 volts AC.

8. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Lower current and higher voltage.
The chest should rise or inflate.
1 amp.
Inductance.

9. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
They should be made by the same manufacturer.
200 volts AC.
Hyperventilation.
Check to make sure that the victim is not still in contact with the electricity.

10. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Check to make sure that the victim is not still in contact with the electricity.
25 feet.
Current changing constantly in magnitude and periodically in direction.
277 volts.

11. 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...
A device used to store electrical energy.
3 -979 Volts.
Tied together
Lower current and higher voltage

12. Not a symptom of electrical shock?.
The motor rotation is reversed.
H terminals.
Because less current flowing at high voltage causes less line loss per kilowatt.
Hyperventilation.

13. A burn causing a blister is classified as a...
Second-degree burn.
Inductance.
Larger than that found in the primary winding.
Full-load - three-phase voltage.

14. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
3 -979 Volts.
Zero amps.
Reverse any two-phase leads.

15. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Derive a neutral for grounding purposes.
The motor rotation is reversed.
1 amp.
Short-circuited after power has been removed.

16. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Allow for metering voltage and Current.
Two speeds
Disconnect the frame-grounding conductor.
Clamp-on ammeter.

17. Current transformers - or CT's - are used to...
150 turns.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Squirrel-cage induction motor.
The chest should rise or inflate.

18. Alternating current may be defined as...
Lower current and higher voltage
Full-load - three-phase voltage.
Potential transformer.
Current that changes constantly in magnitude and periodically in direction.

19. 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.
75 turns.
100 turns.
15 feet off the ground.
5:1.

20. A solenoid coil is...
An electromagnet.
The current will read zero.
800 volts.
They should be made by the same manufacturer.

21. Which of the following does a squirrel cage induction motor have?
Stator windings.
600 volts.
5:1.
Transformer

22. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
H terminals.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Grounded phase and ground fault devices were not operating.
Continuous.

23. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Second-degree burn.
1 amp.
Inductance.
Carotid pulse - which is located in the neck next to the Adam's apple.

24. Where should grounding resistors be located?
Inductance.
At the source transformer.
Reverse its rotation.
Current changing constantly in magnitude and periodically in direction.

25. What is the danger when working around capacitors?
Carotid pulse - which is located in the neck next to the Adam's apple.
At the source transformer.
An electrical shock hazard may exist.
An electromagnet.

26. 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.
800 volts.
Zero amps.
5:1

27. Current in an AC circuit may be measured by...
Clamp-on ammeter.
A device used to store electrical energy.
Disconnect the frame-grounding conductor.
Alternating current.

28. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
The capacitors should be discharged.
5:1
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Squirrel-cage induction motor.

29. How do you change the direction of a 3-phase AC motor?
Two speeds
100 volts.
Squirrel-cage rotor.
Reverse any two-phase leads.

30. The size of a transformer is measured in...
800 volts.
Kilovolt ampere (KVA).
The chest should rise or inflate.
100 turns.

31. Not an acceptable method for the installations of surface transformers?
Circuit Breaker.
Two speeds
They must be installed at least 7 feet above the ground.
Nearly constant.

32. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
Nearly constant.
Draw less current.
Grounded phase and ground fault devices were not operating.

33. Not true about AC power?
Tied together
It provides good speed control.
7 -630 volts.
Reverse its rotation.

34. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Draw less current.
Transformer
The chest should rise or inflate.
480 volts.

35. A transformer with a 1:1 ratio is usually a (an)...
60 Hertz
100 turns.
No.6 AWG.
Isolation transformer.

36. 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.
200 volts AC.
Zero amps.
5:1.

37. What steps up or steps down AC voltage?
Transformer
100 volts.
15 feet off the ground.
A step-up transformer.

38. When not connected to a load - the secondary leads of a current transformer should be...
800 volts.
Hyperventilation.
Shunted and taped
Continuous.

39. All transformers step voltage up or down by...
100 volts.
277 volts.
3 -979 Volts.
Inductance.

40. AC voltage is raised or lowered by means of...
Check to make sure that the victim is not still in contact with the electricity.
Transformers.
Inductance.
X.

41. The standard frequency of alternating current used at a mine is...
Tied together
Potential transformer.
100 volts.
60 Hertz

42. The purpose of a zig-zag transformer is to...
Check to make sure that the victim is not still in contact with the electricity.
Kilovolt ampere (KVA).
Electro-magnetism for their operation.
Derive a neutral for grounding purposes.

43. The transformer used only to measure voltage is a...
Potential transformer.
Transformer
200 volts AC.
Reverse its rotation.

44. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Stator windings.
They should be made by the same manufacturer.
Larger than that found in the primary winding.

45. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A grounding resistor.
7 -630 volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
An electromagnet.

46. Operating coils - motors - transformers - relays and solenoids depend upon...
They should be made by the same manufacturer.
2000 watts
Electro-magnetism for their operation.
Lower current and higher voltage.

47. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Squirrel-cage rotor.
Clamp-on ammeter.
25 feet.
100 volts.

48. 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.
100 turns.
X.
5:1
Two speeds

49. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
100 volts.
60 cycles per second (60 Hertz).
An electrical shock hazard may exist.

50. 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?
Draw less current.
100 turns.
Current changing constantly in magnitude and periodically in direction.
At the source transformer.