Determination of capacities method
Foreword
The method for determining the export commercial capacities is carried out in the following stages :
- Calculation of the physical flows on all network facilities,
- Determination of the physical margins available,
- Transformation of the physical margins into available commercial capacities.
Learn more on D-2 and D-1 process.
1. Hypotheses
An exchange capacity calculation is carried out according to a set of given hypotheses and a certain time period. Among the hypotheses the following elements are to be found :
- State of the French transmission network,
- State of the transmission network of neighbouring TSOs (models simplified in some cases),
- French consumption forecast (extraction in MW per network node),
- French generation forecast (injection in MW per network node),
- Exchanges already known or exchange forecasts.
RTE controls the French consumption forecast process and develops co-operation with its partners to reduce the uncertainties with regard to the other hypotheses.
These hypotheses improve the closer one gets to the day for which the study is performed. The values calculated by RTE are therefore always indicative and may change in time depending on the events affecting the calculation hypotheses.
2. Calculation of the physical flows on all the facilities of the network
According to the hypotheses selected for the study considered, RTE calculates the breakdown of the flows on the network (or load flow). Once this calculation has been completed, the active and reactive power values on all the facilities (lines and transformers) of the network are available.
3. Determination of the physical margins available
RTE determines the physical margins on the network facilities so that any incident has a minimum impact on its customers. Using the initial situation as a basis, a number of incidents mainly corresponding to the outages of network lines are therefore simulated. The physical flows after an incident are compared to the acceptable physical limits of the network facilities. A facility is said to be undergoing constraint when the acceptable physical limits have been exceeded.
The incidents which must be taken into account and the definition of the acceptable consequences with regard to the operating safety of the power system (in terms of current in the lines, voltage stability, consumption shedding, etc.) are specified in RTE's operating rules. Thus one can detect the existence of any constraints (one also refers to congestion) which may affect the "internal" facilities of the network or the interconnection lines. The physical capacity still available, or physical margin, on each of the network facilities is determined.
4. Transformation of physical margins into available commercial capacities
RTE calculates the commercial capacities on the basis of the physical margins by using in particular factors called influencing factors.
The influencing factor of an exchange, in a given direction, on facility 1 after the outage of facility 2, is the impact of a volume of additional exchanges on the physical transit through facility 1 after the outage of facility 2. This factor is expressed in % and in relative value. For example, saying that an exchange from France to Belgium has an influence of 10% on facility 1 after the outage of facility 2, means that 100 MW of exchanges from France to Belgium increase the physical flow by 10 MW on facility 1 after the outage of facility 2.
The physical margin on a given facility is transformed into commercial capacity available on each of the interconnections: this margin is divided up equally on each interconnection and one takes into account the influencing factors of an additional exchange on the interconnection, on the physical flow of the facility for the incident considered.
This transformation of physical margin into commercial capacity is carried out for all the facilities of the French grid. The commercial capacity available on each interconnection is finally defined as being the minimum value of the calculated commercial capacities from all studied outages. This available commercial capacity, shared between the different timeframes of allocation, therefore meets all of the constraints studied.
The commercial capacity available at each timeframe of allocation (yearly, monthly and daily – on most of the interconnections) is defined under the term ATC (Available Transfer Capacity) according to the ENTSO-E meaning.
- More information :
