The aim of the study was to investigate the effects of the introduction of an impedance grounding of the transformer star points on the 150 kV high-voltage grid and the substations under the following questions:
- Appropriate size of the impedances for setting the short-circuit current in accordance with the requirements of the protection concept
- Effects in operation and in various errors and necessary fault shutdown times
- Effects on the insulation coordination, increase of the earth-fault factor, changes in the fault transients and switching transients
- Estimation of the risks due to the short-term shift of the star-point voltage for the high-voltage devices
- Effect on the grounding systems of the substations and on possible ohmic and electromagnetic influences
The short-circuit calculations were done using a extensive model of the 150 and 11/22 kV power grid in Neplan.