# Help please generator impedance question

Discussion in 'Homework Help' started by Ryza, Aug 9, 2011.

1. ### Ryza Thread Starter New Member

Jun 12, 2011
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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?

2. ### Kermit2 AAC Fanatic!

Feb 5, 2010
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If you attempt the explanation first, then somebody here can help you with any mistakes you make. We don't provide a homework completion service, just help with it.

3. ### Ryza Thread Starter New Member

Jun 12, 2011
15
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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.

4. ### Ryza Thread Starter New Member

Jun 12, 2011
15
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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.

5. ### Ryza Thread Starter New Member

Jun 12, 2011
15
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does anyone recommend ebooks on electrical and instrument engineering?..

6. ### abhaymv Active Member

Aug 6, 2011
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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

Nov 21, 2006
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