Impact case study database

DC power enables more efficient electrical power transmission but requires careful integration within the existing AC grid to maximise its potential. The Cardiff Centre for Integrated Renewable Energy Generation and Supply advanced the capacity, cost-effectiveness, and reliability of DC electrical transmission systems within UK and Europe across three key areas:

• The Angle-DC connection: a £15 million project for Europe’s first AC to DC retrofit, designed to increase network capacity and regional economic growth.

• Developed and de-risked control strategies for connecting offshore DC power, saving the National Grid at least £10M.

• Enabled the introduction of DC circuit breakers into transmission systems, building National Grid’s confidence for strategic HVDC infrastructure projects.

4.1 The Angle-DC Connection

The Angle-DC project is an industrial pilot project led by Scottish Power Electrical Networks (SPEN) to overcome limitations of the existing infrastructure connecting the Isle of Anglesey with Bangor by retrofitting AC circuits to MVDC. James Yu, the Future Network Manager at SPEN, noted that Cardiff was selected as the project’s academic partner in recognition of twelve years of “ extensive and acknowledged research work”, and that it was “ the strongest and most suitable institution to support the development of the investment case” [5.1].

Cardiff’s wide-ranging support for the investment case – including simulation studies, models, and technical recommendations – resulted in Ofgem announcing a £13.5M investment in the Angle-DC project, with an additional £1.5M invested by SPEN (£15M total investment) [5.1]. The project completed the MVDC link between Anglesey and Bangor in April 2020, with functionality tests and full commission completed by end of July 2020 [5.1].

By allowing a better utilisation of existing assets, additional network operational capacity has been made available. Conversion of the existing 24.8MW AC circuit to MVDC increased transmission capacity by 23%. SPEN stated: “ *The [MVDC] link has increased the operational power transfer capability between Anglesey and mainland by 30.5MW.*” [5.1] SPEN further confirmed that, following the transmission increase, the “ previously normally open” (meaning unused) transmission corridor between Anglesey and Bangor is now permanently connected [5.1]. Based on the trial validation period 2020-2050, SPEN forecast around £18.67M in economic energy savings and annual reduction of CO₂ of 128 tonnes a year, worth £20M in carbon benefits [5.1].

The scale of the Angle-DC project enabled further impact through economic and social benefits that SPEN confirmed “ Cardiff was instrumental in supporting” [5.1]. Between 2016 and 2020 the project created 200 FTE jobs (80 FTE direct and 120 FTE indirect positions) [5.1]. Through the jobs created, and with wider economic benefits from additional community engagements undertaken by the company , SPEN estimated that the project led to “socio-economic impact of at least £20 million” [5.1].

Angle-DC has been enthusiastically received by Welsh Government, who in a report discussing the Angle-DC project, anticipated future low-carbon economic growth in North Wales through widespread “ripple effects across the system” [5.2, p.18 ] linked to increased renewable power whilst enabling greater transmission efficiency using existing infrastructure. Based on the success of Angle-DC, 25 additional projects across the UK are now being actively investigated [5.1] that could see significant economic and functional benefits to electrical transmission. SPEN forecast that the projects could bring economic impacts of £69.2M by 2030, escalating to £396M by 2050.

4.2 HVDC for National Grid offshore transmission

DC networks have a lower impedance than AC systems of equivalent rating and exhibit faster fault propagation and a higher rate of change in fault currents. Control strategies and protective devices are thus required for the safe and reliable operation of HVDC grids. Tools, such as the Cardiff-led BEST PATHS [5.3] simulation toolbox for HVDC grid-connection of offshore wind farms integral to transmission system operators, manufacturers, and companies for system studies, design, and performance improvement [5.4]. Cardiff also influenced grid design for National Grid through multiple Network Innovation Allowance (NIA) projects, including a) testing of control strategies for HVDC grids and b) investigation into DC circuit breakers, as detailed below.

a. Control strategies for HVDC grids

In 2012, Cardiff began collaborating with National Grid to investigate Voltage Source Converter-based (VSC) HVDC technology for integrating offshore wind power into onshore grids and interconnection with neighbouring countries. While the potential of VSC links was recognised, National Grid had not yet implemented VSC-HVDC converters in their transmission system prior to the NIA projects . National Grid’s significant interest in HVDC control systems relates to HDVC systems suitability in high-power applications, such as the 2.2GW Western HVDC Link and offshore DC links for integration of large-scale wind farms. Paul Gallagher, Head of Innovation at National Grid confirmed that ensuring reliability of such high-power links is critical with “ potentially significant direct impacts on the NGET’s network assets/performance” [5.5].

National Grid confirmed the Cardiff-developed VSC Control Strategy rectified the management of risks associated with introducing new technology into British electricity transmission networks , thereby “ derisking the failure caused by improper operation and control of HVDC systems” [5.5]. Recognising that the overall savings of new HVDC operation and control strategies is approximately £100M, National Grid specifically highlight the “ autonomous converter control proposed by Cardiff University contributes up to 5% savings against this cost, i.e. £5 million” [5.5].

National Grid also note that the successful implementation of the control strategies was enabled by extensive testing at Cardiff. Delayed commissioning or interrupted HVDC links cost National Grid “ of the order of £5 million per month” [5.5] with potential for additional further costs. The validation of operation within the Cardiff test-rig led National Grid to “ identify these potential problems before contract placement and allow the above costs to be avoided” [5.5]. This represents a further £5M in economic savings.

b. DC circuit breakers

Between July 2012 and November 2017, Cardiff collaborated with National Grid on an NIA project (NGET0060) that investigated DC circuit breakers for HVDC grids [3.3]. Prior to this project, no DC Circuit Breaker was available for such application [5.5], meaning a single fault would affect an entire DC network, limiting the deployment of DC grids. Cardiff’s investigations into reliable and cost-effective protective devices and protection strategies formed “ an essential component of the risk managed introduction of the DC circuit breaker into the transmission system” [5.5]. National Grid further stated: “ The main impact of the research outcome is that it directly built up confidence for the HVDC links in the technical roadmap developed by National Grid” [5.5].

National Grid confirmed that the implications of Cardiff’s research translated into development of several strategic and operational plans. Specifically, National Grid specified the research informed development of National Grid Risk Registers, Policy Statements and “ Technical Specifications relating to both strategies and assets for fault management for high power DC applications” for projects such as the GW-level Eastern HVDC Link: a proposed 400kV link between Aberdeenshire and North Yorkshire [5.5].

4.3 Summary

Cardiff’s research into converting medium- and high-voltage systems enabled Europe’s first upgrade of an idle AC transmission corridor to a 30MW medium-voltage DC link, creating 200 jobs and £35M of economic impact. Further research created and verified control strategies for offshore DC connections for National Grid, saving at least £10M through greater efficiency and risk mitigation, and enabled confidence in UK-wide strategies for large-scale high-voltage DC infrastructure projects.