According to Paragraph 5.2 of Annex 1 of Regulation (EC) No. 714/2009 of the European Parliament and of the Council of 13 July 2009, the transmission system operator (TSO) shall publish a scheme for the calculation of the interconnection capacity for the different timeframes, based upon the electrical and physical realities of the network.
The cross-border interconnection capacity values are calculated as follows:
- The Total Transfer Capacity (TTC) between transmission networks of different countries is calculated for the 330 kV transmission network subject to the criteria required for ensuring safety of the electricity supply;
- The Transmission Reliability Margin (TRM) is calculated by analysing the statistics of capacity flow deviation in the particular section for the previous period. The capacity flow deviation is the difference between the estimated and actual capacity flow in the cross-border section;
- The Net Transfer Capacity (NTC) is calculated by deducting the transmission reliability value from the maximum transfer capacity;
- The Already Allocated Capacity (AAC) is the total capacity value that has been actually allocated for trade according to the results of the electricity market session;
- The Available Transmission Capacity (ATC) is the portion of the NTC for the market that has remained and is available during each trade interval after each electricity trade session.
The cross-border transfer capacity is calculated by taking into account the electrical and technical parameters of the 330 kV transmission network, including the length of power transmission lines, nominal current values, power transmission line resistance, etc. The transmission network modes and cross-border transfer capacities are calculated by using the PSS/E software and in compliance with the transparency and confidentiality principles set forth in EC Regulation No. 714/2009.
AST is calculating the maximum cross-border transfer capacity and the allocated capacity of the 330 kV transmission network by considering the peculiarities and technical limitations of the network. The calculation scheme is based on peculiarities and parameters of the real network, the data of the 330 kV transmission lines in the territory of Latvia.
The maximum cross-border transmission capacity is calculated according to the methodology approved by the Baltic countries and countries of the BRELL electric ring, Methodological Instructions regarding Stability in the Electric Ring of Energy Systems of Belarus, Russia, Estonia, Latvia and Lithuania. Calculation of cross-border trade transfer capacity of the Baltic countries is carried out in accordance with the regulations approved by the TSOs of the Baltic countries.
As of 1 January 2016, the power transmission capacities in the Baltics are calculated and allocated according to the document Terms, Conditions and Methodologies on Cross-Zonal Capacity Calculation, Provision and Allocation within the Baltic states and with the 3rd Countries jointly developed by the power transmission system operators of the Baltic countries JSC Augstsprieguma tīkls, AS Elering and AB Litgrid and accepted by the public utility regulators of these countries (document in English). Thus, from 1 January 2016 the annual, monthly and weekly transfer capacities are calculated in accordance with the above Methodology.
BRELL documents (in Russian) that are mentioned in the Methodology and that are not prohibited for publishing:
National Regulatory Authorities of Latvia and Estonia have assessed and endorsed the rules for the calculation and allocation of cross-border capacities with the third countries. “Methodology on cross-zonal capacity calculation and allocation with Russia” will apply from 13 October, 2021. The Methodology was developed by Latvian and Estonian transmission system operators (TSOs) Augstsprieguma tīkls and Elering.
Public Utilities Commission on November 16, 2018 approved "Capacity calculation methodology within the Baltic Capacity Calculation Region". Subject to provisions for the implementation of the methodology as detailed within 15.1 section are fulfilled, this methodology should become effective in 2019.