3.5 Examples of DER Grid Codes for Advanced Functions

3.5.1 European 2003 Blackout and Updated Grid Codes

On September 28 2003, large parts of Italy and portions of neighboring companies experienced a blackout . The primary cause was transmission problems in Germany and Switzerland, but the ultimate result was a rapid cascading of equipment that tripped off. Of interest to distribution utilities is that about 1700 MW of DER generation precipitously tripped off-line when the frequency reached 49 Hz. This caused an even more rapid cascading effect as this generation was lost.

In part because of this event, the European power industry determined that in areas of distribution grids with increased amount of dispersed generation capacity, certain electrical faults could no longer be managed by the existing protection schemes to avoid unintentional islanding or undefined system conditions.  “Consequently the risk of serious system disturbances due to an uncoordinated disconnection of a high amount of distributed generation corresponding to a multiple of the available primary control power reserve cannot be excluded anymore. It can be foreseen that the resulting system balance might be managed only by the activation of large scale underfrequency load shedding.”

Therefore, the decision was made to require DER systems to “ride-through” short-term spikes and sags of voltage and frequency. At the request of ENTSO-E (the European Network of Transmission System Operators for Electricity), several European countries, led by Germany and Italy, have updated the interconnection requirements of new distributed generating units in order to ensure the disconnection thresholds are set to deviations beyond 47.5 Hz or 51.5 Hz. In addition, Germany and Italy started large programs to upgrade (or retrofit) most of the existing noncompliant units to these new thresholds. The upgrade programs were expected to be finalized by end of 2014. No exact cost figures have yet been firmly established for this retrofitting requirement,  After analysis and revisions to the grid codes, the larger DER systems were refitted to include ride-through functionality, but at great cost. This cost has not been fully determined, but additional concerns by ENSTO-E are leading to additional retrofits and other programs for minimizing the risk of major blackouts.

Subsequently, in an international effort to develop the communications requirements for enabling these DER functions, the International Electrotechnical Commission (IEC) expanded these requirements in the communications standard IEC/TR 61850-90-7. This communications standard provides interoperability for DER systems across all DER manufacturers. In Germany, the key DER functionalities are mandated and enabled and the communications protocols have been specified so that utilities can monitor these DER systems, update their settings, and issue commands.