Generator Transient & Subtransient Reactance
Generator Transient & Subtransient Reactance
(OP)
When calculating fault currents for a generator (400 volt 1250kva for example), I thought that we would use the subtransient reactance, X"d. However, I have just read a paper on short circuit currents that states "for salient pole alternators, subtransient reactance is negligible".
Can anyone explain what this might mean?
Can anyone explain what this might mean?






RE: Generator Transient & Subtransient Reactance
RE: Generator Transient & Subtransient Reactance
RE: Generator Transient & Subtransient Reactance
RE: Generator Transient & Subtransient Reactance
Anyway, this method would indicate short-circuit levels to be unrealistically low - or am I missing something?
RE: Generator Transient & Subtransient Reactance
RE: Generator Transient & Subtransient Reactance
RE: Generator Transient & Subtransient Reactance
IEEE Std 141 (Red Book) gives typical Xd'' & Xd' values for Salient pole as well as Turbo-machines. Refer Annexure 4A. There is also a note there indicating that Xd' for Salient pole machines is not normally used in Short circuit calculations.
The Xd'' values for Turbo-machines and Salient pole machines are in the range 9-15% and 16-21% respectively. Corresponding Xd' values are 15-23% for Turbo-machines and 33% for Salient pole machines.
RE: Generator Transient & Subtransient Reactance
This is because the subtransient stage in generators would not last for more than 100ms (or 5cycles).
Hope you find it useful.
RE: Generator Transient & Subtransient Reactance