Automatic last measures (VDE-AR-N 4142)

Automatic last measures are adopted in case of malfunctions and hazards, if there is not enough time for manual measures. The new Application Rule VDE-AR-N 4142 is valid from April 01, 2020 and replaces the FNN guideline on automatic frequency relief or AFE (German automatische Frequenzentlastung)

In a nutshell

  • The Application Rule implements requirements of the European Network Code on Emergency and Restoration (NC ER)
  • Updating of underfrequency-dependent load shedding ensures its effectiveness in the future

Manual or automatic final measures play a major role in case of malfunctions and hazards. In critical grid situations, they make a decisive contribution to the safe and reliable operation of the European electricity supply system.

As a rule, manual final measures taken by transmission and distribution system operators are sufficient. These measures are already defined in the cascade requirements (VDE-AR-N 4140). These include, for example, the reduction of in-feed from generation plants in the event of grid constraints. Automatic final measures are only used in exceptional cases if there is not enough time to carry out manual measures.

The Network Code on Emergency and Restoration (EU Regulation 2017/2196) defines EU-wide binding requirements for automatic final measures. The VDE-Application Rule VDE-AR-N 4142 implements these requirements for Germany. In the Application Rule, the Network Code distinguishes between:

  • Measures for underfrequency-dependent load shedding
  • Measures in case of overfrequency
  • Measures to avoid a stress collapse

Automatic final measures for underfrequency were already defined with the introduction of interconnected operation ("5-step plan"). This concept was part of the Transmission Code 2007; an adaptation was made in 2012 with the FNN guideline "Technical requirements for automatic frequency relief". It described measures to ensure the effectiveness of load shedding even with an increasing number of distributed generation plants in the distribution grids. This included the underfrequency triggering depending on the direction of active power and the appropriate determination of the loads per load shedding stage. The new Application Rule updates specifications from the FNN guideline to include the new requirements from the European Network Code ER.

Concrete innovations

  • Determination of the discharge capacity based on the total load
  • Expansion to ten frequency levels
  • Option of group-shedding concepts with several network operators
  • Detailed monitoring and reporting

Target groups

  • Transmission system operator
  • Distribution system operator
  • Network customers connected to public networks

Benefits and improvement

The Application Rule defines automatic final measures which must be implemented as a precautionary measure to prevent system failures. It describes the monitoring to check the effectiveness of the automatic actions. The Application Rule is the basis for a standardized and binding implementation of automatic last measures in Germany.

Source of supply

The Application Rule VDE-AR-N 4142 is available as a preliminary version. Following notification by the EU Commission and adoption, it will become part of the VDE regulations.