Distributed generation over and under frequency protection

Previously the over and under frequency protection of distributed generation was developed with relatively low overall capacities in mind. With increasing penetration of distributed generation, in certain situations these protection settings could lead to unintended consequences. One example is the 50.2 Hz problem. Until the introduction of the low voltage directive in 2012, generators connected to the low-voltage grid – including solar power systems – were required to disconnect from the public grid as soon as the grid frequency exceeded 50.2 hertz. If the instantaneous loss of generation exceeded 3 GW it would possibly lead to an European wide blackout. Reaching a system frequency value of 50.2 Hz during normal operations is as yet quite unlikely. Just if a high feed-in coincident with a major grid error the grid frequency may exceed 50.2 hertz. Last time the European grid frequency was above 50.2Hz due to a major grid error in 2006. In order to prevent such situations, the German government initialised several retrofit programmes for distributed generation units.

In several related projects, Ecofys has been commissioned to investigate the impact of distributed generation (DG) on the system frequency stability and to develop solutions for any adverse impacts.  For solar generation, we developed a detailed retrofit strategy in collaboration with industry and ministries, which is technically justifiable, easy to implement and politically feasible. Ecofys also used a multi-stakeholder assessment to develop several lists, which served as a basis for planning and monitoring the retrofit programme. We defined the content of the lists, collected the data required by manufacturers and did a plausibility check of the data received. In addition, we supported the TSO during the retrofit programme. For the Federal Ministry of Economics Ecofys has extended the analysis to wind power, biomass, CHP and small-scale hydro power plants.


Michael Döring
Energy Systems and Markets
High voltage