Substation Topology Planning: Impact on Voltage Stability and Short-circuit Current

Substation topology planning can be beneficial to reduce redispatch and better utilize existing infrastructure. This could lower the cost of grid operation and expansion. Various optimization methods are available to find substation topologies. These methods have in common that they are based on steady-state load flow calculations. It must be expected that an increasing grid utilization comes with negative effects on the dynamic stability. This study identifies these possible consequences of grid reconfiguration. A voltage stability study is performed, comparing a meshed grid against two reconfigured grid topologies. It shows that the greatest impact is expected to be on short-term voltage recovery. Depending on the system state and fault location, the permissible voltage limits may be exceeded. These effects are localized and depend on the changes in electrical distances. Such consequences can be mitigated by the use of dynamic reactive power compensation. However, it is clear that substation topologies based on steady-state optimizations need to be examined regarding the impact on voltage stability. With the topological changes, short-circuit currents can be reduced. This could be beneficial for some locations to comply the short-circuit breaker's capacities, but negative for others with an already low short-circuit ratio.