Within the framework of this project, GridCon, as part of a small working group of the distribution network operators Westfalen Weser Netz, EWE, Energienetz Mitte and Wesernetz, thermally dimensioned the earthing connection between the transformer tank and earthing bar in local network stations on the basis of a jointly developed standard procedure.
In particular, the low-voltage-side short circuit between the winding/bushing and the transformer tank was also included in the dimensioning, as this demands the highest standards of protection and fault disconnection. The fault duration that is relevant for the thermal design was determined from the fuse characteristics and the break-times of the overcurrent protection. On the basis of coordinated worst-case assumptions, standardized preferred cross-sections were determined for the voltage levels 10, 20 and 30 kV as well as transformer rated powers from 250 up to 2,500 kVA.
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