Explain the reason of not assigning a single impedance value for a generator. What are the impedances applicable for a generator starting from the moment of a short circuit to reaching a steady state and how are the values normally considered in rating calculations?

 

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The impedance of a system is the effective value of resistance and reactance of a system expressed in ohms. The effective value has to be calculated properly adding series and parallel combination of the various elements resistance and reactance in the vectorial form. Therefore impedance value is specific to the particular system and must be recalculated for any addition or deletion of any element. Impedances are phases or vectors with different angles cannot be arithmetically added, they all must be referred to a common voltage the impedance is depending on the system voltage.

 

A generator/alternator is not a passive component, it does not have a fixed impedance that does not change when there is a short circuit. Under short circuit conditions they have a much lower initial impedance which increases gradually to a steady state value. The reasons for this are the Armature Reaction and the reduction of the field current during a terminal fault in excitation systems directly taking power from the generator terminals.

 

does anyone recommend ebooks on electrical and instrument engineering?..

 

Electical technology(Vol. 2) by Theraja and theraja is good for transformers motors etc.(see google books)

the same volume 4 has topics on instruments but I recomend the book on instrumentation by David A Bell

 

Look here :

http://cr4.globalspec.com/thread/63480

and here:

http://www.eng-tips.com/threadminder.cfm?pid=237

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