Substation
A node in the electrical grid where voltage is transformed, circuits are switched, and faults are isolated. Substations sit between generation, Electric Power Transmission, and Electric Power Distribution — power may pass through several substations at different voltage levels between generator and consumer.
Types
| Type | Function | Flexibility relevance |
|---|---|---|
| Transmission | Connects transmission lines, may transform between voltage levels | Grid-level balancing point |
| Distribution | Steps down to medium voltage (2.4–33 kV) for local feeders | Key boundary between TSO and DSO domains; where flexibility coordination happens |
| Collector | Aggregates DER output (wind/solar farms) and steps up to transmission | Where variable generation enters the grid |
| Converter | HVDC/AC-DC conversion, frequency conversion | Enables cross-border flexibility trading |
| Switching | Single-voltage switching, fault isolation | Network reconfiguration |
Key components
- Transformers — voltage conversion
- Circuit breakers — automatic fault current interruption
- Disconnect switches — manual isolation for maintenance
- Busbars — internal conductors
- SCADA — remote monitoring and control (substations are typically unattended)
- Surge arrestors — lightning/switching surge protection
- Modern substations may use IEC 61850 communication standard
Relevance to flexibility
Distribution substations are the critical boundary between the transmission grid (TSO) and distribution grid (DSO). As DER penetration increases, these become points where:
- Bidirectional power flows must be monitored and managed
- Local Congestion Management decisions are made
- Flexibility services are coordinated between TSO and DSO
- Measurement and settlement of flexibility takes place
The physical capacity of a distribution substation transformer sets a hard limit on how much power can flow in either direction — this is often where Congestion Management bottlenecks appear as local solar generation or EV charging exceeds transformer ratings.