The CNTC approach is built on the current NTC approach, aiming to develop the current NTC approach further in order to fulfill the requirements laid down in the CACM Regulation. The main difference between the current NTC and CNTC approach is that CGMs are applied in the CNTC approach. The CNTC approach is using basic AC load flow and dynamic simulations as a point of departure. In CNTC, the cross-zonal capacities on bidding zone borders are calculated border by border to both directions using CGMs.
The following inputs are needed for the calculations:
CGMs;
GSKs;
Contingencies;
Operational security limits.
Mathematical description of the capacity calculation approach
The AC load flow analysis forms the basis for the CNTC approach. Inputs to the capacity calculation are a CGM, which presents the forecasted state of the power system, GSKs, contingencies, and operational security limits. The AC load flow analysis reveals the voltages in different nodes (magnitude and angle), power flows (active and reactive power) and losses on different transmission lines. Voltages and power flows in the transmission system can be calculated when load and generation in different nodes are known.
Active and reactive power flows in steady state can be calculated using the following equation:
) (j
) (
j i Gi Li Ti Gi Li Ti
i
i P Q P P P Q Q Q
S
Si is the net apparent power coming to node i Pi is the net active power coming to node i Qi is the net reactive power coming to node i
PGi is the active power coming to node i from the connected generators PLi is the active power from node i to the connected load
PTi is the active power going from node i to the connected transmission lines QGi is the reactive power coming to node i from the connected generators QLi is the reactive power from node i to the connected load
QTi is the reactive power going from node i to the connected transmission lines Background on the power flow equations is presented in more detail in Annex IV.
The TTC is the maximum allowed power exchange of active power between adjoining bidding zones respecting N-1 criteria and operational security limits taking into account remedial actions, rules for undue discrimination and rules for efficiently sharing the power flow capabilities of CNEs among different bidding zone borders.
Rules for calculating cross-zonal capacity, including the rules for efficiently sharing the power flow capabilities of CNEs among different bidding zone borders
The CNTC approach shall, in accordance with Article 29(8) of the CACM Regulation:
a) use CGM, GSKs and contingences to calculate maximum power exchange on bidding zone borders, which shall equal the maximum calculated power exchange between two bidding zones on either side of the bidding zone border respecting operational security limits;
b) adjust maximum power exchange using RAs taken into account in capacity calculation;
c) adjust maximum power exchange, applying rules for avoiding undue discrimination between internal and cross-zonal power exchanges;
d) apply the rules for efficiently sharing the power flow capabilities of different CNEs among different bidding zone borders;
e) calculate cross-zonal capacity, which shall equal to maximum power exchange adjusted according to b), c), and d), and taking into account RM and previously allocated cross-zonal capacity.
Point a)
The calculation of the maximum power exchange on a bidding zone border consists of AC load flow analysis and, where appropriate, dynamic analysis. As long as there are no European CGMs that allow for dynamic simulations, offline dynamic simulations applying Nordic CGMs are performed.
The calculation of maximum power exchanges is an iterative process, where the starting point is the CGM for the studied hour (i.e. the CGM includes the forecasted state of the power system). The
calculation of the maximum power exchanges on bidding zone borders consists of contingency analyses taking into account relevant operational security limits. Generation on both sides of the studied borders is scaled stepwise in order to increase the power flow on the studied bidding zone border. After each step (i.e. after each increase in power exchange), contingency analysis (N-1 criterion) is performed and it is checked that operational security limits are not violated. The power flow between the bidding zones can be increased as long as there are no violations of the operational security limits. The analysis is completed, when the maximum power exchange, that still respects operational security limits, is found.
Dynamic simulations are performed, where appropriate, in order to take into account dynamic limits and to ensure operational security.
Point b) and c)
The maximum power exchange is adjusted by using RAs and by applying rules for undue discrimination between internal and cross-zonal power exchanges.
Point d)
Sharing rules may be applied for interdependent bidding zone borders to share cross-zonal capacities efficiently among the different bidding zone borders in situations where full cross-zonal capacity cannot
be given to all bidding zone borders simultaneously due to operational security reasons. The zone-to-zone PTDF matrix may be used to evaluate on which bidding zone-to-zone borders sharing rules may be applied.
The guiding principle in the application of sharing rules is that the sharing rules applied shall ensure the maximization of cross-zonal trading possibilities. Sharing rules are defined by an iterative method
adjusting the power flows on interdependent cross-zonal borders in order to find simultaneously feasible maximum power exchanges on those borders for each CGM scenario. Sharing rules are defined
separately for each CGM scenario in order to take into account the forecasted state of the power system and share the cross-zonal capacities for interdependent borders in the most optimal and efficient way.
Re-evaluation of the interdependencies between bidding zones borders shall be carried out regularly in accordance with the timeframe set in Article 31 of the CACM Regulation, and shall be made available by the CCC together with a justification for the applied sharing rules.
Point e)
Finally, the RM and the previously-allocated cross-zonal capacity are taken into account. It means that cross-zonal capacities are reduced by the amount of RM, and previously allocated capacity.
Article 25: Rules for sharing the power flow capabilities of CNEs among different
4.24CCRs
Cross-zonal capacities on bidding zone borders between CCR Nordic and neighbouring CCRs shall be calculated using CGMs and relevant information from these adjoining bidding zones in coordination with the neighbouring CCC(s). If there is difference in the cross-zonal capacity on the bidding zone border to the neighbouring CCR, the lower value of the cross-zonal capacity shall be used for the capacity
allocation.
Article 26: Methodology for the validation of cross-zonal capacity
4.25Each TSO shall perform the validation of cross-zonal capacities on its bidding zone border(s) in the same way as for the day-ahead market timeframe.
For the CNTC approach, the rules for splitting the corrections of cross-zonal capacity shall follow the same sharing rules as described for calculating cross-zonal capacity for the CNTC approach. The TSOs shall reduce the cross-zonal capacity in a manner that minimizes the negative impact on the market by applying these same rules.
Article 27: Reassessment frequency of cross-zonal capacity for the intraday timeframe
4.26Due to the fact that the intraday gate opening takes place before CGMs for the intraday market timeframe are available, the first assessment of intraday cross-zonal capacity shall be done based on CGMs for the day-ahead market timeframe and the results of the single day-ahead coupling. The cross-zonal capacity shall be released to the intraday market without undue delay. As soon as CGMs for the
intraday market timeframe are available, the cross-zonal capacities shall be reassessed. The frequency of the reassessment of the intraday cross-zonal capacity is dependent on the availability of input data relevant for capacity calculation (e.g. CGMs), as well as any events impacting the cross-zonal capacity.