COP26 case studies
Low voltage DC

Growing international awareness of the environment has increased the urgent need to reduce carbon emissions within the electricity, transport, and building sectors. Traditional low voltage alternating current (LVAC) public distribution systems are now facing pressure to connect large numbers of small-scale renewables such as micro-wind and solar panels. This is in addition to the need for supplying the increased low carbon heat demand such as heat pumps and the increased transport demand such as electric vehicles.

However, existing electricity distribution systems were not originally designed for accommodating such changes. As a result, significantly increased power flow capacity and reduced energy waste will be required over and above the provision of smart controls. Such challenges increase the need for a rethink of the new standard designs to be adopted in the last mile of public electricity distribution networks. Low voltage direct current (LVDC) distribution systems, combined with smart controls, have the potential to facilitate this transformation with advantages over the corresponding LVAC systems.

The use of LVDC systems is not new. The first public electricity supply introduced in 1882 (Edison’s Pearl Street Station) was an LVDC. Since that time AC has dominated due to the capability of AC for transmitting power over long distances. In today’s digital era and low carbon economy, the use of electronic devices run on DC and microgenerators that generate DC has been rapidly growing. This, in addition to advanced power electronics, has motivated the return of LVDC distribution systems after more than 120 years. They can be used to power different sized data centers, facilitate the connection of end-users’ electronic loads and sources, and potentially to be used in last mile cables to reduce energy losses and increase power capacity.

LVDC systems do, however, present significant safety and protection challenges. DC faults are more difficult to detect and clear. Their associated arcs are more aggressive than in AC, and they require longer time to be cleared. This makes the risk of fire in DC systems higher than in AC. In addition, the residual current devices (RCDs) which are commonly used in AC systems to protect against electric shocks and fire are not commercially available for DC systems. DC systems will also require AC-DC power electronics converters for providing DC supply. Such interface devices have poor short circuit fault capability and can trip for remote faults. This can lead to substandard protection selectivity and unnecessary disconnection of larger part of the system. Such issues increase the need for fast and reliable DC protection solutions that reduce the risk and the cost of operating such systems.

This impact acceleration account (IAA) project has prototyped a novel DC protection scheme that addresses the outstanding challenges for protecting an LVDC last mile distribution network. The scheme concept which provides fast speed and good selectivity level for clearing DC faults on LVDC systems were initially developed during the EPSRC Transformation of the Top and Tail of Energy Networks project.