Improvement of the Performance of Scheduled Stepwise Power Programme Changes within the European Power System

Since the deregulation of the electrical energy market, the technical realisation of power transactions based on energy market contracts often effects large stepwise power programme changes – especially at the change of the hour. Due to mainly economic reasons these stepwise power programme changes lead to remarkable power imbalances within the European Power System causing large unintended frequency deviations.

In case of these – mostly negative – frequency deviations up to Δf = -150 mHz, considerably more than half of the primary control reserve is activated needlessly, which highly stresses the corresponding power generating units and increases the mechanical wear of respective actuators. Therefore, the Uni Stuttgart has investigated the origins of the power imbalances within the framework of a research project on behalf of the VGB Powertech.

One main reason for the occurrence of the described power imbalances is the non-uniform conversion of scheduled stepwise power programme changes as rampwise changes of the actual power outputs with different ramp durations and gradients respectively, such as fast power output decreases of hydro power plants and slow power output increases of inert steam power plant units.

These power imbalances may occur within single control areas or between different control areas. Therefore, as a countermeasure, power output ramps with a standardised ramp duration of 2T ≤ 15 min are required so that no power imbalance occurs during scheduled power programme changes. After extended discussions with power plant and power system operators as well as with power plant dispatchers the described issues will be adopted into a VGB-recommendation which shall be published by VGB Powertech for Germany and Europe.

Subsequently, it is intended to include the main elements of the VGB-recommendation into the rules and recommendations of the UCTE and the national grid codes at a later time. This proceeding is also supported from an executive position among power system operators.