Jan 2017
Electricity Distribution
Transition to low voltage DC distribution networks – Phase 1
Jan 2017
Oct 2017
SP Energy Networks
Anthony Donoghue
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Network Innovation Allowance
LV & 11kV Networks

It is well documented that the shift towards a low carbon society will result in a step change in how electricity is generated and consumed across distribution networks. In particular, the uptake of Low Carbon Technologies (LCTs) such as Electric Vehicles, Photovoltaics and Heat Pumps is reducing the available capacity within LV networks and creating a requirement for costly and time consuming network reinforcement. In fact, the potential UK network reinforcement caused by the uptake of Electric Vehicles alone has been estimated to reach £34bn - £48bn by 2040.

Furthermore, these LCTs are connected to an AC distribution network despite the fact that most consume and generate DC power. This creates the requirement for often low efficiency three stage converters between DC devices and the AC network, increasing both network demand and customer losses and equipment cost.

To overcome the challenges discussed above existing LV AC circuits could be converted to DC networks operation to release additional capacity within existing network infrastructure whilst significantly reducing customer losses. In theory, an LV DC distribution network could support longer LV feeders and reduce the number of secondary substations required to supply an area. This is due to improvements in transfer capacity caused by improved circuit voltage drop and increased cable thermal capacity.  In addition to this, if the losses associated with EV charging were reduced by only 4% using a DC supply UK consumers could save up to £52m annually by 2040. For targeted applications LV DC network operations could deliver significant value to UK electricity consumers in the near future if innovation funding is invested into its development.

However, there are number of technical and commercial challenges which need to be addressed before LVDC can be fully adopted by UK DNOs as a business as usual (BaU) approach to facilitate the uptake of LCTs. Some of these challenges include:

·           The impact on cable ageing when converting existing low voltage AC cables to LV DC at different voltage levels and cable types.

·           The optimal LV DC voltage for distribution networks when considering both customers (reduced losses) and network requirements (increased transfer capacity).

·           How an increased transfer capacity over distance could benefit and change network design practices i.e. longer LV feeders, less secondary substations, smaller cable etc.

·           The H&S requirement for LV DC adoption both within the network and at the point of customer connection.

·           The number of opportunities for UK DNOs to convert existing LV AC circuits to DC including a proven Cost Benefit Analysis (CBA) for different applications demonstrating the financial benefit.

The operational and maintenance requirements for existing LV AC circuits which have been converted to DC i.e. is the impact of a cable fault at DC any more or less severe?
  • Provide DNOs with a proven business case to demonstrate whether low voltage DC networks can be a financially and technically competitive alternative to costly conventional reinforcement and network design.
  • Evaluate and understand the performance of existing low voltage cables under DC operation to provide adequate learnings for the technical and operational requirements of converting LV AC networks to DC operation.
  • Provide a road map of potential applications that could benefit from low voltage DC supplies (rapid EV charging, street lighting) along with a detailed cost benefit analysis using relevant case studies.

Assessment  and quantification of the impact of DC voltages on existing AC cable.

Provision of technical guidance for converting LV AC circuits to LV DC operation.

Development of a clear business case demonstrating benefits of converting circuits to DC under different applications to avoid costly conventional network reinforcement.