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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 type of 3-phase AC motor is used most often around a mine?
Squirrel-cage induction motor.
Zero amps.
X.
Second-degree burn.

2. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
The capacitors should be discharged.
Full-load - three-phase voltage.
25 feet.
The motor rotation is reversed.

3. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
They should be made by the same manufacturer.
75 turns.
No.6 AWG.

4. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
H terminals.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Inductance.

5. What is the first step to be followed in aiding a victim of electrical shock?
277 volts.
12 to 15 times a minute.
Check to make sure that the victim is not still in contact with the electricity.
H terminals.

6. Three-phase AC underground cables must be provided with overcurrent protection using a...
100 turns.
It provides good speed control.
Circuit Breaker.
Derive a neutral for grounding purposes.

7. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Potential transformer.
7 -630 volts.
They must be installed at least 7 feet above the ground.
They should be made by the same manufacturer.

8. AC voltage is raised or lowered by means of...
Potential transformer.
480 volts.
Kilovolt ampere (KVA).
Transformers.

9. 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?
Nearly constant.
Disconnect the frame-grounding conductor.
3 -979 Volts.
They must be installed at least 7 feet above the ground.

10. 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.
5:1
They must be installed at least 7 feet above the ground.
5:1.
Stator windings.

11. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
They must be installed at least 7 feet above the ground.
The sum of the two capacitors.
At the source transformer.

12. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Hyperventilation.
200 volts AC.
Inductance.

13. A transformer with a 1:1 ratio is usually a (an)...
Isolation transformer.
At least two phases
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
2000 watts

14. A burn causing a blister is classified as a...
200 volts AC.
Second-degree burn.
Squirrel-cage induction motor.
Because less current flowing at high voltage causes less line loss per kilowatt.

15. What should the duty rating of a grounding resistor be?
3 -979 Volts.
X.
Shunted and taped
Continuous.

16. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
An electrical shock hazard may exist.
Nearly constant.
Zero amps.
Larger than that found in the primary winding.

17. To protect against over-current in a three-phase circuit over-current protection must be provided for...
1 amp.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
At least two phases
100 volts.

18. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Derive a neutral for grounding purposes.
Inductance.
Grounded phase and ground fault devices were not operating.
It provides good speed control.

19. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Circuit Breaker.
Zero amps.
Hyperventilation.
X.

20. Define alternating current...
A.C.
60 cycles per second (60 Hertz).
Grounded phase and ground fault devices were not operating.
Current changing constantly in magnitude and periodically in direction.

21. 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...
Carotid pulse - which is located in the neck next to the Adam's apple.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
100 volts.
The sum of the two capacitors.

22. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
Because less current flowing at high voltage causes less line loss per kilowatt.
Circuit Breaker.

23. 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.
15 feet off the ground.
277 volts.
Transformers.

24. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Grounded phase and ground fault devices were not operating.
No.6 AWG.
The chest should rise or inflate.
2000 watts

25. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
600 volts.
Grounded phase and ground fault devices were not operating.
7 -630 volts.
Check to make sure that the victim is not still in contact with the electricity.

26. The combined capacitance of two capacitors in parallel is...
A step-up transformer.
The sum of the two capacitors.
Draw less current.
100 volts.

27. 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...
Two speeds
A step-up transformer.
Draw less current.
Continuous.

28. Current transformers - or CT's - are used to...
Check to make sure that the victim is not still in contact with the electricity.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
3 -979 Volts.
They should be made by the same manufacturer.

29. The primary function of a power transformer is to provide...
A.C.
Full-load - three-phase voltage.
200 volts AC.
Kilovolt ampere (KVA).

30. Not an acceptable method for the installations of surface transformers?
1 amp.
2000 watts
They must be installed at least 7 feet above the ground.
At least two phases

31. The purpose of a zig-zag transformer is to...
Cut around clothing that has adhered to the burned area.
Draw less current.
150 turns.
Derive a neutral for grounding purposes.

32. What is the danger when working around capacitors?
60 cycles per second (60 Hertz).
1 amp.
An electrical shock hazard may exist.
Nearly constant.

33. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Lower current and higher voltage.
Two speeds
277 volts.
Current that changes constantly in magnitude and periodically in direction.

34. A wound-rotor induction motor has all the following EXCEPT...
Current that changes constantly in magnitude and periodically in direction.
Carotid pulse - which is located in the neck next to the Adam's apple.
Squirrel-cage rotor.
A step-up transformer.

35. 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...
It provides good speed control.
At least two phases
Tied together
Electro-magnetism for their operation.

36. How should clothing be removed from a burn?
Cut around clothing that has adhered to the burned area.
600 volts.
Squirrel-cage rotor.
Alternating current.

37. The standard frequency of power supplied by the power company is...
2000 watts
75 turns.
1 amp.
60 cycles per second (60 Hertz).

38. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
12 to 15 times a minute.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Current that changes constantly in magnitude and periodically in direction.
They must be installed at least 7 feet above the ground.

39. The main function of CT's and PT's on a main substation is to...
Full-load - three-phase voltage.
Allow for metering voltage and Current.
Disconnect the frame-grounding conductor.
A step-up transformer.

40. How do you change the direction of a 3-phase AC motor?
277 volts.
Reverse any two-phase leads.
Cut around clothing that has adhered to the burned area.
Stator windings.

41. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Electro-magnetism for their operation.
Because less current flowing at high voltage causes less line loss per kilowatt.
A step-up transformer.

42. 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.
800 volts.
100 turns.
The current will read zero.

43. Not true about AC power?
Reverse any two-phase leads.
3 -979 Volts.
No.6 AWG.
It provides good speed control.

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

45. 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...
200 volts AC.
Clamp-on ammeter.
A device used to store electrical energy.
Draw less current.

46. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Cut around clothing that has adhered to the burned area.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Squirrel-cage rotor.
No.6 AWG.

47. 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?
600 volts.
No.6 AWG.
75 turns.
Second-degree burn.

48. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
200 volts AC.
Inductance.
No.6 AWG.
25 feet.

49. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
An electromagnet.
Disconnect the frame-grounding conductor.
Current that changes constantly in magnitude and periodically in direction.

50. If any two-phase wires are reversed on a three-phase motor - the motor will...
Second-degree burn.
Reverse its rotation.
60 Hertz
They must be installed at least 7 feet above the ground.