Self-healing is the ability of the distribution network to automatically detect, isolate faults and restore service to its normal state. A combination of sensors, software algorithms, local protection systems and automated switches is applied, e.g., breaking the circuit automatically and safely under abnormal conditions such as overloads and short circuit currents. Low voltage (LV) self-healing principally uses healthy sections to assist the loads in a faulty section and isolate the fault from the rest of the circuit. Service restoration is performed by automatic reclosing and/or manually by human operators. Centralised and decentralised architectures for self-healing are possible. In the latter case, intelligence is distributed amongst several nodes. It is necessary to distinguish between overhead and underground network structures which are both present in the current power systems in Europe, implying different designs for LV self-healing.
Highlights
Regulatory incentives may need to be designed for the scalability of LV self-healing in case it is proven as beneficial to society.
Challenges and opportunities for DSOs
Opportunities:
- Self-healing allows for quicker fault detection and isolation when combined with adequate measurements and smart metering, possibly providing additional insights into the faults. The reduction of fault duration and impact leads to improved service quality. Fault detection and insights are not exclusively linked to self-healing itself, but offer an integral approach with other aspects of the smart grid.
- Impacts related to extreme weather events (for overhead grids) or cyberattacks can be automatically reconfigured and restored, improving resilience. For normal faults, self-healing helps improve power quality, identify operational problems and provide efficiency in solving problems.
- Challenges:
- Business case. At the LV level utilities generally do not have equipment providing data on transformers (voltage, current, power) nor the possibility of remote opening and closing. Benefits, such as potential CAIDI-related improvements, should overweigh costs for investments needed for more intelligence. Potential benefits could also be realised in terms of effective deployment flexibility and avoiding or postponing grid reinforcements.
- Not all grid structures are suitable for self-healing grid functionalities. For instance, switching is not directly suitable in radial networks, but more suitable in a ring or a meshed structure. Moreover, activation of flexibility from decentralised generation can be challenging because the detection system may not be fit for the purpose. Post-fault schemes need to be defined.
- Technological developments for sensors, actuators for automation and remote control. The quality of telecommunication solutions should support real-time interaction between components that functions in all situations. The management of decentralised intelligence, update and maintenance of software and cybersecurity in general are also a concern.
- A balance between a centralised and decentralised architecture should be sought for automatic intervention.
Challenges:
- Organisational. Changing fault handling and restoration requires active participation and confidence in the solution within the DSOs.
EDSO Considerations
- At the moment, self-healing is mainly applied to medium voltage (MV) grids, given the network structure, design of switches, protections and the impact on connected parties, providing a better business case than at LV. Implementation of LV self-healing is in its early stages, especially because it is not directly suitable for radial networks, business case aspects etc.
- Operational experience is needed for full-fledged implementation of self-healing. A gradual implementation from a partial to fully automatic mechanism can be considered together with a gradual deployment of monitoring and control devices for increased electric vehicle (EV) and distributed energy resource (DER) penetration.
Potential use cases
- Self-healing through microgrid and distributed battery energy storage systems (BESS). Decentralised control architecture by using DER (such as BESS) to enable islanded operation of the LV network, when a fault occurs on the upstream network.
- Supply of critical clients (police stations, hospitals, etc.) connected to the LV grid. Non-discriminatory criteria need to be evaluated at the national level.
- An integral smart grid approach, not limited to but including self-healing, could help balance loads from congested networks (e.g., with high concentration of EVs, heat pumps etc.) with other networks with excess capacity and, hence, potentially reduce/postpone grid reinforcement needs.
- For LV grids, resettable fuses are used (e.g., by Stedin) in LV cables after dormancy due to previously detected faults, which are difficult to identify. The automatic fuse responds to the set short-circuit characteristics and automatically switches on again after a few seconds.
Ongoing projects
- RESOLVD Horizon 2020 project (more info).
- Stedin and E-REDES do not have, nor had in the past, self-healing projects at the LV level but only at the MV level. UFD does not have self-healing projects either at MV or at LV. As indicated, the LV network must be meshed, and it is necessary to install automatic switches in the LV panels of secondary substations.
Last update: 17 May 2024