Introduction: The European Union Renewable Energy Directive has committed the Member States to National targets for renewable energy production such that at least 20% of the EU’s energy will be produced from renewable sources by 2020. Meanwhile, the creation of an internal market for energy remains one of the EU’s priority objectives. The development of an interconnected internal market will facilitate cross-border exchanges in electricity and improve competition. The potential role of HVDC in integrating renewable energy generation and cross-border electricity exchanges is widely recognised and many ideas for dc grids linking the transmission systems of different countries and renewable generation are being promoted.

At present, no dc circuit-breaker is commercially available and any dc fault will affect the entire dc network. A dc grid is, therefore, restricted to a single protection zone at present and the capacity of generation connected to it may not exceed the infrequent infeed loss risk limit prescribed by the Security and Quality of Supply Standard. The dc circuit-breaker is therefore an essential technology in enabling the concept of a dc grid to develop.

Objectives:

The objective of the proposed work is to understand the application issues associated with dc circuit-breakers in dc grids. The work will study the impact of dc circuit-breaker operation on the dc system, the HVDC converters and the connected ac systems. In particular, the challenges presented by protection and fault clearance in dc grids will be addressed. The work forms an essential component of the risk-managed introduction of the dc circuit-breaker onto the transmission system in accordance with PS(T)013. The results of the work will inform technical specifications and risk-registers for the dc circuit-breaker and for the protection and control of dc grids.

The project will deliver reports on the results of studies of the system behaviour and the results of experiments performed on a model (low voltage simulation) dc circuit-breaker in the analogue HVDC test facility at Cardiff University. The work complements a closely-related project at the University of Manchester which aims to study the electrical operating environment of the dc circuit-breaker and derive design and test requirements for the device itself. 

Expected Benefits: This project is successful if we improve the understanding of the issues associated with application of dc circuit breakers. There is a high likelihood that such studies will allow application issues to be identified, better understood and enable their mitigation to be evaluated. The work will contribute significantly to the specification of requirements for dc circuit breakers and protection for dc grids.