An agreement with VGB (the technically based association of power plant owners and manufacturers headquartered in Germany) allows us to exchange information and attend each other’s meetings. This was a meeting for VGB members to hear the results of a study on the above topic by the Universities of Rostock and Stuttgart, led by Professor Harald Weber and Florian Gutekunst, using two differing approaches. One study used an overall model (Copper-plate model), the other was in more detail, with simulations of the supergrid lines in the EU system. Both models were used for the analysis of the transient frequency behaviour of the system.
Broadly, the Copper-plate model showed there could be some problems with stability as renewable capacities were increased in the future, while the detailed model seemed to suggest that, especially with the planned HVDC lines from Northern Germany to Western and Southern parts of the country, there would not be insurmountable difficulties. Constant power devices as they become more prevalent could contribute to regulation of the grid. Too high a proportion of hydro-electric power capacity would actually reduce the stability of the system, as these plants can pulsate. This is a well-known thing (but not previously to me) with hydro plants, caused by pressure pulsations within the penstocks (inlet water channels).
A representative from ESB, Ireland (Marios Zarifakis) was invited to present some of his own slides to highlight the effects of grid frequency and voltage transients on the power plants themselves. There can be huge reversals of power, and, sometimes, resonances with different sections of the turbine may occur if frequency changes happen too fast. Plant suppliers have told him that a rate of change of frequency of 0.5 Hz/s is acceptable, but that the effect of greater rates of change, say 1 Hz/s, needs investigation. Mr Zarifakis painted a graphic picture in extremis of the large, fast-rotating low-pressure turbine blades ending up in the power plant staff car park! I don’t think this has happened yet, but I think we had better not let the renewables contribution to capacity get too large. Who said renewables were the most friendly power plants? 20% of synchronous capacity (fossil or nuclear) seems like the absolute safe minimum.
Discussions centred on how to use the universities study, for example producing versions for public education and for generators, and on getting the message across that plants could potentially be highly affected by rapid transients.
My German is almost non-existent but the meeting was conducted in English. The lowest point was when the first presenter asked if there was anyone present who did not speak German well. Fortunately, I was not entirely alone. Incidentally, the lunch, courtesy of VGB, was extremely good, so I am glad that we at IEA CCC treat the VGB representative well at our meetings!