Learnings

Outcomes

The main output of the project is around better understanding of Cold Start and its implications in terms of network operation. This allowed for areas of key focus for future work to be defined. 

The project created:

•       a model of 11kV network and used different LCT uptake and outage scenarios to investigate Cold Start data from simulation 

•       insights into network performance (further described below in key findings)

•       a series of recommendations based on the insights (further described in Lessons Learnt)

The project delivered successfully insights into network behavior in a Cold Start scenarios based on a realistic model for loads, network and future low carbon technology uptake.

The key findings of the project included:

•       The peak demand after outages can be more than double the no-outage value, both at the level of the whole network and in terms of per-customer demand, when considering 2030 levels of LCT uptake.

•       Following a 24 hour power outage, the longest duration outage that was studied, peak demand can last for up to three hours and power flows can take up to 10 hours to return to baseline levels.

•       Even for the shorter outages studied (8 hours) peak demand increased by almost 75%.

•       Compared to the present day, After Diversity Maximum Demand (ADMD) values were 25% higher in the 2030 no-outage case, but increased further after the power outage by almost 100% to over 4kW per consumer.

•       Outage duration was seen to have the most significant impact on peak demand following the outage. LCT uptake scenario choice and restoration time/day had an observable but less significant impact.

•       LV feeder segments can experience up to 50% overloading, even for the 8 hour outage. However, only a small minority of these overloading events lasted longer than 20 minutes.

•       Possible approaches to mitigate Cold Start effects include operational policies, network controls, demand-side flexibility and conventional reinforcement.

•       Re-energising the full network after Cold Start could cause protection relay or fuse tripping, but this was not studied.

The findings were then presented to key internal and external stakeholders. Based on this some recommended steps were agreed and insights were included into future planning scenarios.

Lessons Learnt

From the key findings of the project, the following learnings were generated:

This project was a limited study and there are many points that would support a wider understanding of CLPU and potential mitigations and these are being explored through development of new projects.

A key contribution of this work is providing evidence that Cold Start impacts in 2030 are significant for outages as short as eight hours – with the potential for more rapid LCT uptake, as proposed in the recent “Ten Point Plan”, to bring forward the time horizon when significant impacts may be expected and for higher LCT uptake to further reduce the minimum outage length that causes issues.
 

The following areas for future investigation and next steps were recommended:

•       Incorporation of findings into ongoing network planning and operational processes:

Target network regions with highest risk of adverse effects from CLPU: While this study used network information from UK Power Networks, the findings are relevant to other DNOs since we have used a generic LV modelling approach based on the Transform Model which was developed based on input from all network operators, and since all regions are expected to see significant levels of LCT uptake in coming years. In particular, the results show the significant impact of Cold Start on load diversity in areas with near-future levels of LCT uptake. However, rates of LCT uptake may be different in different areas due to geographical and socioeconomic factors, and so the time horizon at which effects become significant may also vary across the UK.

Consider both reinforcement and flexibility: a case by case approach might be required to understand the long term financial and service implications of either options and as such an individual business case might need to be created based on assets present at site and likelihood of procuring suitably reliable flexibility in each site

•       Review policies, procedures and standards: Current network operational policies do not account for cold start implications in network design in detail and there is a need to review this with associated engineering standards and procedures

•       Consider broader significance such as implications in:

Black Start planning: The key consideration in Black Start is sequencing restoration of generation and demand to energise the complete system while maintaining safe and stable operation. We did not consider the generation side in our work, but results on future CLPU effects would inform the rate at which demand can be reconnected for a given generation capacity if outages are prolonged;

Active network management: Actively managing the network through different technological solution should be investigated for potential avoidance of cold start effects;

Smart appliance rollout: From the perspective of the network’s demand customers, we believe that these results contribute further evidence that deploying smart appliances, including for electrified transport and heating, will bring benefits to all customers – in this case, through the potential to avoid or mitigate secondary loss of power following re-energisation if the EV chargers or electric heating systems can limit or postpone demand until the network can accommodate their load. The terms under which such load management takes place should, however, be carefully considered in order to avoid undue impacts on individual domestic customers, particularly vulnerable customers, and it is unlikely that all such demand will be shiftable. We envisage that in general postponement of EV charging will be more acceptable than restricted heating, but any mechanisms should allow individual domestic customers’ circumstances to be taken into account;

Protection operation: This might be impacted by the elevated after diversity demand after restoration which can interfere functions at LV level unless addressed by protection operation;Analyse sensitivity of impacts on network to characteristics e.g. housing stock & LCT uptake to support investment planning in network upgrades

Assess potential management methods (incl. impact on vulnerable customers) to explore lowest cost mitigation approaches: It is recommended to work towards including targeted network investment plans in future development plans.

The findings and recommendations have been shared across internal and external stakeholders. They are being integrated into policies looking into future planning and are being used to define scope for other innovative work in projects exploring black start scenarios and heat.

One caveat is that this project studied only one particular 11kV feeder with representative LV feeders, meaning that there may be some limitations in terms of wider rollout. However, we consider that the measures set out above would provide significant value if applied as a business as usual approach. In the long term these steps would contribute to improved awareness of, and ability to mitigate risks of, adverse outcomes from Cold Start – through new or improved business processes to manage the new demands, and leading to better consumer experience (including vulnerable customers) during Cold Start events.