IEC 60909 - Idc parameter

[SindhuK]

Hello,

I was looking at the old post related to Idc parameter of IEC 60909 study. Below is the link for the thread.

http://www.eng-tips.com/viewthread.cfm?qid=248832

Does anyone know what happened at the end ? Thanks

I am trying to understand how the standard or ETAP calculates the X/R ratio values using Method C in determining the Idc parameter.
The formula is mentioned in the manual, but it appears that actual X/R values were not used for this calculation.

http://files.engineering.com/getfile.aspx?folder=5...

Any insight into the calculation of Idc and Method C X/R is appreciated.

thanks

 

[7anoter4]

By definition maximum Idc=A=sqrt(2)*I"k. Applying a d.c. voltage in a L-R circuit we have:
L*di/dt+R*i=Vdc or L*di2/dt2+R*di/dt=0.The solution of this differential equation it is as following :
i=Imax*e^(-R/L*t) where Imax=A and L=X/(2*pi()*frq) then:
idc=sqrt(2)*I"k*e^(-R/X*(2*pi()*frq)*t).
R and X are total circuit parameters-from source up to short-circuit location.
You have to reduce the circuitry according Thevenin rule:
V=I*Zth+Vth
In short-circuit case V=0 and Isc=-Vth/Zth where Vth=c*Vrated.
Table 1 are the standard recommendations for maximum and minimum factors of supply voltage with respect to the rated.
For meshed networks there are some methods in 4.3 chapter.

 

[7anoter4]

I think you are referring to IEC 60909-0/2001 chapter 4.3.1.2 Short circuits in meshed networks.
[Method] c) Equivalent frequency fc.
But, in my opinion, it is for the peak short-circuit current ip, in meshed networks, calculation, only and not for idc calculation.
You could find in IEC 60909-1 ch. 2.4.3 Factor κ of parallel R-L-Z branches.
Equation no.75 gives the exact factor k general for all 3 methods.