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. What steps up or steps down AC voltage?
15 feet off the ground.
No.6 AWG.
The chest should rise or inflate.
Transformer

2. The property of an electric circuit that opposes any change in current is called...
Lower current and higher voltage.
25 feet.
Inductance.
Full-load - three-phase voltage.

3. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
The current will read zero.
Draw less current.
277 volts.
Two speeds

4. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Draw less current.
A grounding resistor.
The sum of the two capacitors.

5. 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
1 amp.
Squirrel-cage rotor.
200 volts AC.

6. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
60 cycles per second (60 Hertz).
7 -630 volts.
H terminals.
Potential transformer.

7. What type motor is a wound-rotor induction motor?
A.C.
75 turns.
Inductance.
X.

8. 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.
100 turns.
5:1.
Reverse its rotation.
Larger than that found in the primary winding.

9. 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...
Second-degree burn.
Isolation transformer.
Larger than that found in the primary winding.
Tied together

10. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
No.6 AWG.
Short-circuited after power has been removed.
Electro-magnetism for their operation.
Kilovolt ampere (KVA).

11. The speed of an alternating current - squirrel-cage induction motor is...
Short-circuited after power has been removed.
Nearly constant.
Shunted and taped
Clamp-on ammeter.

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

13. A wound-rotor induction motor has all the following EXCEPT...
Lower current and higher voltage.
Allow for metering voltage and Current.
Continuous.
Squirrel-cage rotor.

14. Not a symptom of electrical shock?.
An electromagnet.
150 turns.
Grounded phase and ground fault devices were not operating.
Hyperventilation.

15. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Alternating current.
Because less current flowing at high voltage causes less line loss per kilowatt.
They must be installed at least 7 feet above the ground.

16. A transformer with 1 -500 turns in the primary winding has a primary voltage of 2 -400 volts and a secondary voltage of 120 volts. How many turns are in the secondary winding?
At least two phases
Because less current flowing at high voltage causes less line loss per kilowatt.
Kilovolt ampere (KVA).
75 turns.

17. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
1 amp.
Draw less current.
Because less current flowing at high voltage causes less line loss per kilowatt.
Four times less than that of the secondary.

18. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Shunted and taped
The capacitors should be discharged.
Larger than that found in the primary winding.
Reverse its rotation.

19. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Transformers.
The current will read zero.
A step-up transformer.
Nearly constant.

20. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Capacitance.
Allow for metering voltage and Current.
Disconnect the frame-grounding conductor.
12 to 15 times a minute.

21. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
Kilovolt ampere (KVA).
2000 watts
Transformer
At the source transformer.

22. A control power transformer...
1 amp.
Reverse any two-phase leads.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Lower current and higher voltage

23. What should the duty rating of a grounding resistor be?
Full-load - three-phase voltage.
Nearly constant.
They should be made by the same manufacturer.
Continuous.

24. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
The capacitors should be discharged.
Short-circuited after power has been removed.
A device used to store electrical energy.
They should be made by the same manufacturer.

25. 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...
100 volts.
Zero amps.
Draw less current.
Potential transformer.

26. High voltage is used to transmit power over long distances...
7 -630 volts.
Two speeds
800 volts.
Because less current flowing at high voltage causes less line loss per kilowatt.

27. Operating coils - motors - transformers - relays and solenoids depend upon...
75 turns.
No.6 AWG.
Circuit Breaker.
Electro-magnetism for their operation.

28. 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?
100 turns.
3 -979 Volts.
H terminals.
The current will read zero.

29. A burn causing a blister is classified as a...
Second-degree burn.
Clamp-on ammeter.
Allow for metering voltage and Current.
Nearly constant.

30. What type of 3-phase AC motor is used most often around a mine?
15 feet off the ground.
Squirrel-cage induction motor.
75 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.

31. At what rate should mouth-to-mouth resuscitation be applied?
Two speeds
The motor rotation is reversed.
Inductance.
12 to 15 times a minute.

32. The combined capacitance of two capacitors in parallel is...
At the source transformer.
100 volts.
The sum of the two capacitors.
Clamp-on ammeter.

33. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
The sum of the two capacitors.
Draw less current.
25 feet.
A device used to store electrical energy.

34. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
A step-up transformer.
60 Hertz
Lower current and higher voltage
Zero amps.

35. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Carotid pulse - which is located in the neck next to the Adam's apple.
480 volts.
Two speeds
A device used to store electrical energy.

36. Alternating current may be defined as...
5:1
Hyperventilation.
Derive a neutral for grounding purposes.
Current that changes constantly in magnitude and periodically in direction.

37. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Zero amps.
The motor rotation is reversed.
A device used to store electrical energy.
Squirrel-cage induction motor.

38. What is the danger when working around capacitors?
100 turns.
A step-up transformer.
75 turns.
An electrical shock hazard may exist.

39. 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...
An electrical shock hazard may exist.
Draw less current.
Shunted and taped
Alternating current.

40. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
The capacitors should be discharged.
Capacitance.
Four times less than that of the secondary.
A.C.

41. 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?
Capacitance.
It provides good speed control.
200 volts AC.
Derive a neutral for grounding purposes.

42. The transformer used only to measure voltage is a...
Potential transformer.
Squirrel-cage induction motor.
25 feet.
7 -630 volts.

43. 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?
Inductance.
800 volts.
Potential transformer.
480 volts.

44. How should clothing be removed from a burn?
A step-up transformer.
At the source transformer.
Stator windings.
Cut around clothing that has adhered to the burned area.

45. Not an acceptable method for the installations of surface transformers?
A.C.
They must be installed at least 7 feet above the ground.
Transformer
100 turns.

46. Define alternating current...
Carotid pulse - which is located in the neck next to the Adam's apple.
The chest should rise or inflate.
Current changing constantly in magnitude and periodically in direction.
Continuous.

47. What is the first step to be followed in aiding a victim of electrical shock?
Four times less than that of the secondary.
A device used to store electrical energy.
5:1.
Check to make sure that the victim is not still in contact with the electricity.

48. Compared to the secondary of a loaded - step-down transformer - the primary has...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
The current will read zero.
No.6 AWG.
Lower current and higher voltage

49. 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?
Alternating current.
75 turns.
Reverse any two-phase leads.
Zero amps.

50. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
No.6 AWG.
Short-circuited after power has been removed.
They must be installed at least 7 feet above the ground.
A.C.