Short-circuit calculation with IEC363

[HVmariner]

Hi all!

I am currently trying to calculate following IEC363 standard the short-circuit current on the secondary side of a distribution transfomer supplied by 3 6.6kV generators of different powers. Would any-one know if it possible to avoid using the "equivalent generator" method described in this standard? If yes, how could I proceed?

Thanks in advance...

 

[hheid]

Hi,
Would you please clarify in which page this method is described or please send a copy to me.

With Best Regards,

 

[HVmariner]

In fact it is not clearly explained. To understand this, it is necessary to read very carefully what is written in chapter 8.5 page 71 (especially the last paragraph):

"If the effects of the primary circuit components cannot be neglected, then the impedance due
to the transformer must be added to the (equivalent) generator impedance, and new time
constants evaluated. These new parameters may then be used to determine the timedependent
short-circuit currents as outlined in 8.2."


Finally, after thinking for a long time about that and trying to carry out simple hand calculations to understand this, my conclusion is that it is necessary to use this complicated equivalent generator method.

Regards,

 

[rbulsara]

I am not familiar with IEC's detailed terminology or process, but electricity does not know the difference, so the end results should be the same, regardless of the procedures employed.

Could it mean equivalent impedances of the multiple generators (and any other impedance such as cable, or other contributing sources)? It would be a reduction of generator impedances in parallel, in sereis with the transformer impedance.(All impedances converted to a common base if using PU method)

By time dependent SCC do you mean SCC values during different phases? E.g: first 1/2 cycle substransitent (X&quotstate , trasnient (X') state and steady state (X)??

If you are using a software, its should take care of everything automatically for you.

Sorry if I did not understand your question correctly.

 

[jbartos]

Suggestion: The equivalent generator impedance may be considered equal to zero, i.e. complex zero 0+j0, p.u., if the load, kVA or MVA, considered is substantially smaller than the generator kVA (kW) or MVA (MW) rating. In this case, the "infinite bus" is considered. The impedance will be equal to complex zero, and voltage will be Eg=1.0, p.u.
IEEE Standards are using Zsys and Vsys for the power supply system input to the short circuit calculations.
If the load is relatively large with respect to the generator rating, the generator equivalent impedance should be considered to obtain accurate short circuit current results. The equivalent generator impedance is in series with the transformer impedance.

 

[jbartos]

Suggestion: Visit

http://www.dcmt.bc.ca/PDF DOCS/SCC Rep R1.pdf

etc. for more info