Reducing the risks of network restoration with our 'soft energisation' approach

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Soft energisation: reliable, safe and fully controlled high-voltage network restoration
Power disruptions due to blackouts must be kept to a minimum. When energising a transmission network, the variety of components and high voltages and currents involved make system restoration technically complex. So it is essential for Transmission System Operators (TSO) to have a controlled, reliable and safe method to restore transmission networks. System restoration should also minimise stress on network components – too much electrical stress from a restart could damage components or trigger protection devices, plunging the network into another blackout.

The traditional process for restoration is based on ‘switching’ overhead lines, cables and transformers. However, because the network supply is not that firm, due to a limited short-cirrcuit level, due to relatively low generation capacity availability, this approach can easily lead to voltage oscillations. Furthermore, assets are exposed to severe electrical stress which can lead to damage and further network component trips.

Soft energisation
To reduce the risk of transient voltage oscillations and triggering follow-up blackouts, DNV in conjunction with Dutch TSO TenneT and energy supplier ENGIE have developed and tested an approach for transmission network restoration, based on the principle of soft energisation. It enables reliable system recovery for any network, with a lower risk profile for the network assets involved.

Benefits of soft energisation

• Reliable, safe and fully controlled
• System restoration is typically successful first time 
• No stress or risk of damage during live tests 
• Applicable to any network of any size in any country and involving any components
• Not all components need to be tested yearly
• Provides competitive advantage in restoration facility tendering because limited feasibility studies are needed
• A small generator can be used to energise a network of any size
• Soft energisation of step-up transformers makes it possible to start additional power plants and increase short circuit level, hardening the network

Whole network restoration
Soft energisation can energise any network with limited feasibility studies beforehand. Because the soft-energisation methodology causes no transient / oscillation phenomena, complex transient studies and impact assessment are not needed. Also, as the process is fully controlled, one rather small generator can safely energise the whole network.

Download our approach to system restoration based on soft energisation, including its successful trial on TenneT’s network in the northern Netherlands. You can also contact us directly for more information.