Grounding using FCDIST module of CDEGS
Grounding using FCDIST module of CDEGS
(OP)
I am looking for the actual 12 kV (Star) ground fault current flowing into a grounding system using FCDIST module of CDEGS. What I have is SLG 6025 A at LV distribution side (12 kV) and 2382 A at HV side (66 kV Delta ). The distribution side has three phases and a single neutral cable. HV side is without OHSW. Having these information,how can I model model LV side using FCDIST?






RE: Grounding using FCDIST module of CDEGS
I usually model distribution lines as a typical length with the "end station" grid resistance equal to the average pole ground resistance. For 69 kV faults (the worst case for faults in the substation), the source current of distribution lines is zero.
RE: Grounding using FCDIST module of CDEGS
RE: Grounding using FCDIST module of CDEGS
I'm not sure what you are getting at by considering one 69 kV tower away from the station as a central station. The worst case fault will normally be a SLG fault on the 69 kV bus in the substation. The substation will be the central station. The substation at the end of the 69 kV line will be a terminal. The current of importance is the "Total Earth Current" at the central station (your substation). This is what causes GPR, step-voltage, and touch-voltage at the substation.
I don't know why you want to "find which tower directs the maximum current into ground." FCDIST does calculate the current into earth at each tower, but not all of this flows in the substation grid. At towers close to the central station, the earth current flows from the shield wire into earth and ultimately to the terminal substation. At towers close to the terminal station, the earth current flows from earth into the shield wire to get to the terminal station ground grid. Unless you are worried about potentials around the towers, tower earth currents do not need to be considered.
I suggest that you go into CDEGS Help and look at the section "FCDIST: An Overview".
RE: Grounding using FCDIST module of CDEGS
RE: Grounding using FCDIST module of CDEGS
RE: Grounding using FCDIST module of CDEGS
The worst case for GPR at distribution poles may be for a 69 kV fault at the station. In this case, FCDIST will give GPR and earth current at each pole. I recently did an analysis of a facility on a distribution line about a mile from the substation. The 12 kV fault level at the facility was 2919A, of which 46A returned through the earth, causing a 1460V GPR. For a 6700A high side fault at the substation, the earth current at the facility was 470A, with a 11070V GPR, almost as high as the GPR at the substation. This may have been an unusual case because of the relatively high (5.2 ohm) substation grid resistance and high earth resistivity (1220 ohm-m).
RE: Grounding using FCDIST module of CDEGS
RE: Grounding using FCDIST module of CDEGS
RE: Grounding using FCDIST module of CDEGS
RE: Grounding using FCDIST module of CDEGS
I agree that the GPR due to fault at HV side can be transferred to the distribution facilities. In the case I investigated, this was a much worse case than 12 kV faults. That is why I cautioned that considering faults on the 12 kV line (which I think pertained to your original question) may not be sufficient.