It must be obvious to anyone these days that power grids of the future will have to be capable of coping with a rising demand for electrical energy and also incorporate a high proportion of renewable energy sources. Incidentally, regarding these ‘renewables’, an important distinction will have to be drawn between concentrations of wind turbines, hydro dams, large photovoltaic (PV) projects, etc. and far more plentiful, small-scale power handling/generation systems that will be embedded into local distribution networks (e.g. rooftop PV, electric vehicle charging stations, battery storage).
The trend toward increased ‘renewables’ used in the grid and factors such as new end-use applications (e.g. electric vehicles), increased grid utilization and more active consumer involvement have all combined to create a burgeoning worldwide interest in Smart Grids. Key elements for Smart Grids will be information and communication technology to enable a range of new services. These will include active demand, sensors and smart meters – all intended to improve the operation and reliability of the grid. Power electronics will then serve to enable flow control and steering of all this ‘smart’ energy. In particular, the trend to power flow control and steering equipment at medium voltages as well as for large-scale transmission (through super- or overlay-grids) will naturally have an important impact on future testing of equipment.
Now, since almost everything will be electrical – from transport to heating – it will become necessary to strengthen grids, increase their reliability and security, reduce vulnerability and optimize profitability. As part of this process, there is now a clear trend in several regions of the world toward increasing short-circuit power. This, in turn, will lead to high voltage equipment capable of managing short-circuit currents in excess of 80 kA – once viewed as a threshold of sorts but soon about to be surpassed. In fact, generator circuit breakers dealing with fault currents in excess of 200 kA have already been tested.
Some utilities will try to handle this increase in short-circuit levels with (superconducting) fault current limiters that are presently being developed. Indeed, standardization of such limiters is now under discussion at IEEE and they will undoubtedly need massive power for testing once they are applied for high voltages. For example, in order to keep pace with these trends of increased grid strength, we at KEMA are maintaining our short circuit test capability, notwithstanding the high cost of the present generator overhaul program.
Another issue is that power is being transmitted across ever- greater distances due to commercial, geographic (hydro generation connected to mega-cities) and security (i.e. redundancy) reasons. This means that additional components will be needed to stabilize such extended systems. These will include capacitor and shunt reactor banks for AC networks and this implies increased stresses on this equipment from both the dielectric and switching points of view. New test requirements are therefore under study at CIGRE, such as those for series capacitor banks or new fault elimination strategies including single phase or fast auto-reclosure.
New transmission systems are also now either under construction or being planned all over the world, often as an ‘overlay’ to existing grids. For example, Germany has to transport all its wind power from the North Sea, India wants to exploit its hydro resources to the east, while the U.S. needs to connect its windy northern states with the more populated ones to the south and east. In addition, China has its great dams, Brazil is tapping the Amazon to bring power to São Paulo, North Africa is being viewed as able to supply much of Europe with solar power, and so on.
The missing link is of course connecting these disparate grids. As in the days of inventors such as Tesla and Edison, AC and DC are again competing but this time on a gigawatt scale. For the field of testing, this implies that laboratories will have to invest to cover these ultra-high voltage technologies and we at KEMA, for example, have already completed test demonstrations for 1100 kV class breakers. Moreover, recent developments in the field of voltage source converter technology, along with progress in standardization, are together shifting the borders of independent testing towards DC switching.
Future meshed DC grids will need DC circuit breakers, a completely new ‘kid on the block’ and, indeed, studies on the implication of such super grids are already underway. But even for the classical AC breakers, the presence of AC/ DC conversion may pose a few surprises by introducing harmonics into the high voltage grid.
DC cables as well as gas-insulated lines will play an increasingly important role as well – mostly for submarine applications or for densely populated areas due to restrictions on power frequency magnetic field. Another tendency will be to reduce dependence on SF6. Air as well as solid insulation are now steadily phasing out this greenhouse gas in medium voltage switchgear although ‘pensioning off’ SF6 at the high voltage end will present a greater challenge. In East Asia, for example, there is rapid introduction of high-voltage vacuum switchgear and American utilities also seem eager to start pilot projects. We have already tested several such high-voltage vacuum breakers and had to confront various challenges when it came to maintaining a realistic arcing and recovery voltage stress.
On the more traditional component level, test laboratories will no doubt see compact medium power generator breakers, often using vacuum technology and serving middle to large size local generation units. The recent commissioning of the EES (electrical energy storage) laboratory at our facility in the U.S. is one example of such a new laboratory, dedicated to a key smart-grid component. Another area with coming test needs will be batteries for community storage and electric vehicles. KEMA’s Flex Power Grid lab is one such new facility that deals with power conversion equipment for smart distribution grids.
So, the lesson is clear. The testing world will need not only to observe all these tendencies of the future but also invest to provide the services needed to make them become reality that much sooner.
Professor Rene Smeets