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AC Theory ch 31
Understanding the Design and Function of AC Generators
| Question | Answer |
|---|---|
| 1. Another name for an AC generator is the ___ | alternator |
| 2. What is the primary difference between a simple DC generator and a simple AC generator | Dc uses a comutator AC uses slip rings and brushes |
| 3. There are two basic types of altenator. These are the revolving ___ type and the revolving ___ type | Armature Field |
| 4. Slip rings, unlike the segmented commutator, are contructed as a ___ ring, with each end of the armature loop connected to a seperate ___ | continuous, ring |
| 5. In a 3-phase generator, the three sets of windings are placed ___ apart. | 120 degrees |
| 6. What limits the amount of power that can be generated with the revolving armature type of generator | brushes and slip rings.. page 234 |
| 7.What is the advantae of using a rotating field and a stationary armature on commercial generators | design permits higher kva ratings because he output of circuit is connected to the stator. page 240 |
| 8. The ___ is the rotating member of a generator or motor. | rotor |
| 9. When the armature is held stationary in a generator it is called the ___ | stator |
| 10. Two tpes of rotating field construction are the ___ rotor and the ___ rotor | salient pole, round rotor |
| 11. Pole faces that jut out and are ery pronounced are called ___ poles. | salient poles |
| 12. The ___ rotor uses a smooth, longer, and narrower construction to minimize wind resistance and centrifugal forces | round |
| 13. Exciters are made in a variety of ways including ___ and ___ | stationary, rotating |
| 14. A rotating exciter mounted on the same shaft as the main generator is usually called a ___exciter | brushless |
| 15. Alternators wiht small kVa ratings are usually ___ cooled | Air |
| 16. Air cooled alternator usually have a ___ attached to one end of the rotor to help circulate air. | fan |
| 17. Large-capacity generators are often enclosed in a ___ atmosphere for cooling purposes | hydrogen |
| 18. Which dissipates heat faster, hydrogen or air? | hydrogen |
| 19. What are the factors that determine the frequency of an alternator? | number of poles, speed of rotor |
| 20. What is the mathematical formula for determining the frequency of an alternator? | f = p * s/120 p= # of poles z= speed RPM |
| 21. To generate 50 Hz with an 8-pole generator, the speed of rotation must be ___RPM | 750 RPM |
| 22. How many poles are required for a generator to hae a frequecy of 60 Hz at 1,200 RPM? | P = 6 60 = ( 1,200 * P / 120) |
| 23. A generator has four poles and a speed of 1,500 RPM. what is the output frequency? | 50 Hz 5- = (4 * 1,500) / 120 |
| 24. What three factors determine the output voltage of an alternator? | length of conductors, speed of rotation, strength if magnetic field. |
| 25. How is the output voltage controlled? | increasing or decreasing strength of magnetic field. |
| 26. What three conditions must be met when connection two 3-phase alternators in parallel? | 1) ? 2) outputs must be same frequency 3) all output kVa must be same |
| 27. The most common method of detecting when the direction of the magnetic field of one alternator is matched with the phase rotation of a paralleled alternator is with the use of ___ | 3 lights |
| 28. Using the "Three Lamp" method, houw do yu know when the two alternators are in-phase with each other? | all the lights are out |
| 29. Another method of paralleling two alternator is with the use of a | synchroscope |
Created by:
JoshHampton