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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. Not a symptom of electrical shock?.
Hyperventilation.
7 -630 volts.
The motor rotation is reversed.
Allow for metering voltage and Current.

2. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Continuous.
15 feet off the ground.
7 -630 volts.
A device used to store electrical energy.

3. The speed of an alternating current - squirrel-cage induction motor is...
Disconnect the frame-grounding conductor.
Nearly constant.
Inductance.
5:1.

4. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
They must be installed at least 7 feet above the ground.
5:1.
Grounded phase and ground fault devices were not operating.
200 volts AC.

5. 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...
The sum of the two capacitors.
100 volts.
75 turns.
The current will read zero.

6. Operating coils - motors - transformers - relays and solenoids depend upon...
Draw less current.
Squirrel-cage induction motor.
Hyperventilation.
Electro-magnetism for their operation.

7. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Draw less current.
60 Hertz
The current will read zero.
15 feet off the ground.

8. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
25 feet.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
150 turns.

9. The property of an electrical circuit that opposes any change in voltage is called...
Current changing constantly in magnitude and periodically in direction.
Full-load - three-phase voltage.
Capacitance.
Transformer

10. The property of an electric circuit that opposes any change in current is called...
The capacitors should be discharged.
Current changing constantly in magnitude and periodically in direction.
At least two phases
Inductance.

11. The main function of CT's and PT's on a main substation is to...
5:1.
480 volts.
Allow for metering voltage and Current.
Current that changes constantly in magnitude and periodically in direction.

12. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
A.C.
The current will read zero.
It provides good speed control.
Two speeds

13. Not true about AC power?
Circuit Breaker.
Current that changes constantly in magnitude and periodically in direction.
Four times less than that of the secondary.
It provides good speed control.

14. What steps up or steps down AC voltage?
200 volts AC.
Clamp-on ammeter.
Inductance.
Transformer

15. A wound-rotor induction motor has all the following EXCEPT...
At the source transformer.
Tied together
Clamp-on ammeter.
Squirrel-cage rotor.

16. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
A grounding resistor.
25 feet.
60 Hertz
Cut around clothing that has adhered to the burned area.

17. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
Isolation transformer.
75 turns.
They must be installed at least 7 feet above the ground.

18. The purpose of a zig-zag transformer is to...
Derive a neutral for grounding purposes.
Reverse its rotation.
Transformers.
The chest should rise or inflate.

19. The standard frequency of power supplied by the power company is...
Potential transformer.
No.6 AWG.
Continuous.
60 cycles per second (60 Hertz).

20. Compared to the secondary of a loaded - step-down transformer - the primary has...
At the source transformer.
Lower current and higher voltage.
Shunted and taped
480 volts.

21. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Larger than that found in the primary winding.
1 amp.
15 feet off the ground.
The current will read zero.

22. What position of a selector switch using a voltmeter would you select to check a 120-volt AC circuit to obtain the most accurate reading?
At least two phases
Zero amps.
No.6 AWG.
200 volts AC.

23. Current in an AC circuit may be measured by...
Clamp-on ammeter.
75 turns.
Inductance.
Cut around clothing that has adhered to the burned area.

24. The standard frequency of alternating current used at a mine is...
Transformers.
Squirrel-cage rotor.
2000 watts
60 Hertz

25. AC voltage is raised or lowered by means of...
Inductance.
Disconnect the frame-grounding conductor.
Transformers.
100 turns.

26. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Squirrel-cage rotor.
3 -979 Volts.
The chest should rise or inflate.
An electrical shock hazard may exist.

27. High voltage is used to transmit power over long distances...
A.C.
Because less current flowing at high voltage causes less line loss per kilowatt.
Capacitance.
Potential transformer.

28. All transformers step voltage up or down by...
The current will read zero.
Inductance.
A.C.
An electrical shock hazard may exist.

29. 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?
Zero amps.
100 turns.
Kilovolt ampere (KVA).
They should be made by the same manufacturer.

30. 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.
At least two phases
Allow for metering voltage and Current.
5:1.
Draw less current.

31. Three-phase AC underground cables must be provided with overcurrent protection using a...
An electromagnet.
A.C.
Circuit Breaker.
Reverse any two-phase leads.

32. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Carotid pulse - which is located in the neck next to the Adam's apple.
X.
100 turns.

33. The combined capacitance of two capacitors in parallel is...
At the source transformer.
A device used to store electrical energy.
Draw less current.
The sum of the two capacitors.

34. Not an acceptable method for the installations of surface transformers?
Continuous.
They must be installed at least 7 feet above the ground.
At least two phases
25 feet.

35. Alternating current may be defined as...
Full-load - three-phase voltage.
Check to make sure that the victim is not still in contact with the electricity.
At least two phases
Current that changes constantly in magnitude and periodically in direction.

36. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
600 volts.
Zero amps.
25 feet.
Provides single-phase power to smaller loads such as lights - heaters - etc.

37. 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?
Transformers.
480 volts.
Full-load - three-phase voltage.
800 volts.

38. 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.
Lower current and higher voltage
Two speeds
1 amp.

39. 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.
60 Hertz
Stator windings.
5:1
They should be made by the same manufacturer.

40. What type motor is a wound-rotor induction motor?
480 volts.
A.C.
H terminals.
Four times less than that of the secondary.

41. What is the danger when working around capacitors?
An electrical shock hazard may exist.
Squirrel-cage rotor.
800 volts.
7 -630 volts.

42. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Two speeds
480 volts.
The motor rotation is reversed.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

43. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Four times less than that of the secondary.
12 to 15 times a minute.
Because less current flowing at high voltage causes less line loss per kilowatt.

44. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
The motor rotation is reversed.
Short-circuited after power has been removed.
Shunted and taped
3 -979 Volts.

45. A transformer with a 1:1 ratio is usually a (an)...
Circuit Breaker.
Allow for metering voltage and Current.
Isolation transformer.
5:1

46. The transformer used only to measure voltage is a...
Continuous.
Reverse any two-phase leads.
Potential transformer.
No.6 AWG.

47. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Cut around clothing that has adhered to the burned area.
An electromagnet.
Lower current and higher voltage.
Four times less than that of the secondary.

48. 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.
Tied together
100 turns.
75 turns.

49. What is a capacitor?
At least two phases
2000 watts
Nearly constant.
A device used to store electrical energy.

50. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
A.C.
An electrical shock hazard may exist.
A step-up transformer.
Full-load - three-phase voltage.