Black start capability has historically relied on large thermal generation. These assets provided the strength and controllability needed to re-energise the network following a widespread outage, and restoration strategies were built around their behaviour.
As the generation mix changes, that foundation is shifting.
Renewable generation is typically located at the edges of the network, where system strength is lower. At the same time, the size of the assets being connected continues to increase. This creates a mismatch between network strength and asset size, which becomes particularly relevant during energisation.
Changing assumptions for black start
This has direct implications for black start.
Traditional approaches assume strong system conditions and large, centralised sources. In a network with more distributed and inverter-based generation, those assumptions no longer hold in the same way.
The challenge is not simply how to deliver existing black start capability, but how to deliver it under changing system conditions.
The role of distributed restart
One of the approaches now being explored is distributed restart using grid forming battery energy storage systems.
These systems are capable of establishing voltage and supporting network energisation, allowing restoration to begin from locations that would not traditionally have been considered.
This changes how restoration can be approached. Rather than relying on a small number of large generators, it becomes possible to initiate restoration from distributed sources and progressively bring sections of the network back online.
Energisation remains the constraint
The underlying challenge, however, does not change.
Energising transformers and network circuits introduces transients. Transformer inrush current in particular, can be significant depending on the point on the voltage waveform at which energisation occurs. On stronger networks, this is often absorbed without consequence. On weaker or partially restored networks, it can result in voltage depression and instability.
In this context, black start is not simply about establishing voltage source. It is about how the network is energised around that source, and whether those switching events can be managed in a controlled and predictable way.
From concept to application
A recent Enspec project explored how this can be achieved in practice through a distributed restart approach using grid forming BESS.
The full case study sets out the application in more detail here.
