Electricity networks contain equipment that operates at different voltage levels. Domestic customers are fed from the low voltage (LV) network. The LV network is fed from the high voltage (HV) network. The HV network is fed from the extra high voltage (EHV) network, and so on. When a fault occurs on the HV network, there is a cascading impact to the LV network that it feeds.
In more modern parts of the network, automation is used to prevent an LV outage when there is a HV fault. However, a large proportion of the LV network does not have any automation.
For the majority of LV networks, when a HV fault occurs, the LV network fed from the affected substation loses supply. This means that all customers fed from that substation experience a power cut.
Benefits
With the introduction of LV Interconnected Pairs, restoration times to those affected on the LV network will be reduced due to enhanced automation.
Gross financial benefit if all eligible substations received interconnected pairs technology: £1.75m per year
This is made up of CI and CML benefits.
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[benefit per substation = HV fault rate x customers per substation x time that automation would save]
On average, we estimate that it takes 90 minutes to apply a backfeed.
The potential benefits across LPN, EPN and SPN are technically the same. The actual benefits will vary on a case by case basis based on network behaviour, such as where HV faults occur. This is analogous to the benefits from the Automated Power Restoration Software, which are reported each year in the E6 submission. See page 27 onwards in this document for more information on APRS: http://library.ukpowernetworks.co.uk/library/en/EnvReports201617/Environment%20and%20Innovation%202016-17%20Commentary_Final.pdf
Learnings
Outcomes
The project successfully managed to validate that the proposed scheme is achievable. The design approach was formally signed off by the responsible stakeholders. Physical compatibility of the solution has also been validated due to the successful installation on 26 sites. The project team developed a detailed Network Operational Procedure highlighting all key aspects of the project and the responsible parts of the business associated with them.
Another aspect of the project that can be viewed as an outcome is the established proof-of-concept environment within the ADMS which can be integrated into the live system following a successful business-as-usual transition. Additionally, the modifications to the RTUs can be standardised for future rollout if successful. Lastly, the interface box design has been commercially validated and can now be procured from an existing supplier in the market.
In relation to the next steps in RIIO-ED2, the project team will continue to finalise the installations and commissioning activities under the business funded innovation scheme (BFI). The team will continue to monitor all sites and keep a record of any operations triggered by the solution. Those findings will be documented and used as evidence to support the transition of the solution to business as usual. The project team is also considering expanding the project to the remaining UK Power Networks licence areas to maximise the benefits of this solution.
Lessons Learnt
The key lesson learnt from this project is related to the site selection exercise. In order to identify suitable sites to install this solution, the project team had to go through a multi-stage assessment process which spanned various departments. The initial step was to extract a list of the worst-performing sites in the network. This list was then filtered based on the compatibility of sites with the proposed solution. Following that, a desk-based assessment was carried out on both the potential donor and receiver sites to validate compatibility. All successful sites are then assessed through a site visit to ensure physical compatibility.
As the drop rate between each of the aforementioned stages has been substantial, an investigation was carried out to assess the causes of such results. These can be summarised as follows:
· Geographical distance between the donor and receiver
· Risk of overloading the LV cable
· Inefficient size of the transformers at the receiver site
· Volumes of connected customers
All key project learnings and operational information has been documented on the Network Operational Procedure (NOP) linked to the project in order to ensure future operability and an efficient business transition of the solution.
