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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. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Transformer
They should be made by the same manufacturer.
Nearly constant.
At least two phases

2. Not true about AC power?
At least two phases
It provides good speed control.
Because less current flowing at high voltage causes less line loss per kilowatt.
No.6 AWG.

3. 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.
Larger than that found in the primary winding.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Reverse its rotation.

4. Not a symptom of electrical shock?.
H terminals.
Nearly constant.
Inductance.
Hyperventilation.

5. 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?
Shunted and taped
600 volts.
800 volts.
Reverse its rotation.

6. 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.
Clamp-on ammeter.
Because less current flowing at high voltage causes less line loss per kilowatt.
The motor rotation is reversed.

7. How should clothing be removed from a burn?
A step-up transformer.
7 -630 volts.
Kilovolt ampere (KVA).
Cut around clothing that has adhered to the burned area.

8. Which of the following does a squirrel cage induction motor have?
Stator windings.
100 turns.
Potential transformer.
Derive a neutral for grounding purposes.

9. Where should grounding resistors be located?
They must be installed at least 7 feet above the ground.
At the source transformer.
They should be made by the same manufacturer.
Reverse any two-phase leads.

10. The primary leads of a single-phase transformer should be connected to the...
200 volts AC.
Because less current flowing at high voltage causes less line loss per kilowatt.
H terminals.
The chest should rise or inflate.

11. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Circuit Breaker.
Reverse its rotation.
Hyperventilation.
25 feet.

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

13. Three-phase AC underground cables must be provided with overcurrent protection using a...
Current that changes constantly in magnitude and periodically in direction.
The chest should rise or inflate.
200 volts AC.
Circuit Breaker.

14. How do you change the direction of a 3-phase AC motor?
Circuit Breaker.
Second-degree burn.
Tied together
Reverse any two-phase leads.

15. Compared to the secondary of a loaded - step-down transformer - the primary has...
Reverse any two-phase leads.
A device used to store electrical energy.
100 volts.
Lower current and higher voltage

16. Not an acceptable method for the installations of surface transformers?
Kilovolt ampere (KVA).
A step-up transformer.
They must be installed at least 7 feet above the ground.
12 to 15 times a minute.

17. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
Shunted and taped
100 volts.
Alternating current.

18. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Alternating current.
Clamp-on ammeter.
Short-circuited after power has been removed.
An electromagnet.

19. A transformer with a 1:1 ratio is usually a (an)...
Second-degree burn.
Isolation transformer.
150 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.

20. High voltage is used to transmit power over long distances...
X.
Four times less than that of the secondary.
Because less current flowing at high voltage causes less line loss per kilowatt.
Reverse its rotation.

21. A control power transformer...
Two speeds
Provides single-phase power to smaller loads such as lights - heaters - etc.
Reverse any two-phase leads.
X.

22. Operating coils - motors - transformers - relays and solenoids depend upon...
Reverse its rotation.
No.6 AWG.
Check to make sure that the victim is not still in contact with the electricity.
Electro-magnetism for their operation.

23. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Full-load - three-phase voltage.
15 feet off the ground.
7 -630 volts.
75 turns.

24. What should the duty rating of a grounding resistor be?
Shunted and taped
At least two phases
Continuous.
5:1.

25. What is the danger when working around capacitors?
75 turns.
100 turns.
An electrical shock hazard may exist.
150 turns.

26. 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...
Draw less current.
Zero amps.
Short-circuited after power has been removed.
Transformers.

27. 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.
Lower current and higher voltage.
Transformers.
Cut around clothing that has adhered to the burned area.

28. 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.
Zero amps.
An electromagnet.
Because less current flowing at high voltage causes less line loss per kilowatt.

29. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
Because less current flowing at high voltage causes less line loss per kilowatt.
1 amp.
Zero amps.
A grounding resistor.

30. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
Circuit Breaker.
Second-degree burn.
Provides single-phase power to smaller loads such as lights - heaters - etc.

31. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
X.
A step-up transformer.
The motor rotation is reversed.
Continuous.

32. Compared to the secondary of a loaded - step-down transformer - the primary has...
5:1
Lower current and higher voltage.
1 amp.
Alternating current.

33. What type of 3-phase AC motor is used most often around a mine?
Second-degree burn.
Squirrel-cage induction motor.
Stator windings.
Draw less current.

34. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
150 turns.
Short-circuited after power has been removed.
H terminals.

35. Current transformers - or CT's - are used to...
Squirrel-cage rotor.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
60 cycles per second (60 Hertz).
75 turns.

36. What type motor is a wound-rotor induction motor?
A.C.
The sum of the two capacitors.
Lower current and higher voltage
Current changing constantly in magnitude and periodically in direction.

37. The standard frequency of alternating current used at a mine is...
60 Hertz
3 -979 Volts.
Squirrel-cage induction motor.
1 amp.

38. Alternating current may be defined as...
150 turns.
Current that changes constantly in magnitude and periodically in direction.
Inductance.
A device used to store electrical energy.

39. A burn causing a blister is classified as a...
Shunted and taped
Two speeds
A grounding resistor.
Second-degree burn.

40. The property of an electric circuit that opposes any change in current is called...
Clamp-on ammeter.
Capacitance.
The current will read zero.
Inductance.

41. When not connected to a load - the secondary leads of a current transformer should be...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Shunted and taped
Inductance.
Zero amps.

42. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Derive a neutral for grounding purposes.
5:1
Grounded phase and ground fault devices were not operating.
Two speeds

43. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Allow for metering voltage and Current.
480 volts.
Transformer

44. The main function of CT's and PT's on a main substation is to...
A device used to store electrical energy.
75 turns.
Allow for metering voltage and Current.
Zero amps.

45. The standard frequency of power supplied by the power company is...
100 turns.
A device used to store electrical energy.
60 cycles per second (60 Hertz).
12 to 15 times a minute.

46. The size of a transformer is measured in...
Kilovolt ampere (KVA).
Short-circuited after power has been removed.
Continuous.
At least two phases

47. 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...
Second-degree burn.
480 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.
100 volts.

48. 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?
Cut around clothing that has adhered to the burned area.
5:1.
The current will read zero.
75 turns.

49. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
X.
Potential transformer.
Draw less current.
Provides single-phase power to smaller loads such as lights - heaters - etc.

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?
60 Hertz
The motor rotation is reversed.
100 turns.
Two speeds