Jean-François Ballet, Managing Director of the SuperGrid Institute and Vice-President Industry Projects at Alstom Grid, explains,
“We have structured the SuperGrid Institute into five key programmes to achieve our ambitious goals.”
Programme 1: Supergrid system architecture, operation and control
Developing large DC grids raises a number of technical challenges: DC grid protection against electrical fault, DC voltage transformation, power flow controllability in a meshed system or in a system which involves LCC and VSC technologies, and more. Architecture principles must also allow the co-existence of technologies from different origins. Achieving the right technical performance of future DC grids or combined AC-DC power systems is only possible through simulation. This is because:
- DC grid stability involves much faster dynamics than AC grids, so precise electromagnetic transient simulation is required in which power electronics converter control systems need to be modelled accurately;
- real-time simulation is necessary to demonstrate system performance when integrating a new technology into the grid (for example a new protection scheme).Supergrid simulation in itself is a field for research and development.
Programme 2: Technologies for breaking, insulation and measurement
Programme 2 has the mission to prepare the technological building blocks for future substations. Its first challenge is circuit breaking on DC networks. This question is complex since the current does not pass through zero as in AC. To overcome this problem it is crucial to design a new generation of circuit breakers that opposes a high enough voltage to that of the network to force the current to zero. Different short-circuit conditions and the time needed to eliminate the fault will demand optimised circuit breakers to reduce infrastructure costs.
The second challenge is the optimisation of gas-insulated substations for DC applications. Particular effort will be devoted to the use of solid insulation for DC as well as insulating materials that offer better performance and lower environmental impact. This includes the choice of new gas mixtures to replace SF6.
The third focus area will be the principles of AC-breaking without SF6. Designs using more environment-friendly products should be made available for 145 kV to 1,100 kV circuit breakers for short-circuit current up to 80 kA.
Programme 3: Power conversion technologies
Programme 3 is focused on power electronics technologies to meet the requirements of the future DC grid. Research covers innovative topologies and control to build highly efficient HVDC power converters – in particular for DC/DC conversion – that do not exist today.
Research projects include:
- medium-frequency transformers working at several kHz;
- new generation silicon carbide components to reach blocking voltages of 10 kV and higher;
- integration of transformers, power electronics and control to a very high level of voltage for the power converters.
Programme 4: Supergrid cables and lines
Programme 4 covers the development of specific technological building blocks for cable systems and advanced materials, in particular for meshed HVDC networks. The specifics of meshed grids that could influence the requirements for materials and components of cable systems are:
- new types of power flow variation, transient modes and harmonics;
- new architecture configurations or iterative deployment (in particular offshore).
Hence the need to investigate:
- design optimisation and the development of new components;
- materials ageing;
- the development of advanced materials with improved performance.
Programme 5: Stabilisation and storage
Programme 5 aims at developing more grid flexibility with high capacitive storage. A special focus will be on developing a reversible pump turbine with improved performance:
- more responsiveness and stability during the start and stop of pumped and turbined sequences, to improve stocking or destocking electric energy;
- new turbo-machinery designs for a broader operational area, enabling off-design operation at low discharge flow;
- more operability with low or high head imposed by the plant site. The specifics of long-distance and meshed grids and the hydrologic and geographic conditions (continental and offshore) demand research into new combinations of head and discharge flow with high efficiency.