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Transmission Reliability Margin (TRM) algorithm

This document describes the current state of the algorithm.

To compute the TRM, you will need uncertainties and unintended deviations.

We focus on the uncertainties.
Unintended deviations computation is easy.
It does not require to manipulate networks.
We ignore this computation for now.

Inputs

Market-based network

The market-based network is either a D2CF network or a DACF network.
This network models what the network is expected to be at a future timestamp from a market point of view.
It does not take into account the last minute operations on the network.

Real time snapshot network

The real time snapshot represents what has really happened on the network.

Real time GLSK

The real time GLSK are required to compute the zonal PTDF.

Real time CRAC

The CRAC contains the network actions.

Outputs

Export results to CSV

The results can be exported to a CSV.

Here is the format :

Case date;Branch ID;Branch name;Country Side 1;Country Side 2;Uncertainty;Market-based flow;Reference flow;Zonal PTDF
2024-07-15T13:14:12Z[UTC];toto;FGEN1 11 BLOAD 11 1;FR;BE;12.0;100.0;112.0;-1.0

Algorithm steps

Critical Network Element (CNE) selection

CNE selection

The CNE are selected using the XnecProvider interface.
This means that you can provide your own list of branches or automatically select interconnections or branches with more than 5% zonal PTDF.
You can also do the union or the intersection of such providers.
You can also implement your own provider.
Note that in the TRM algorithm, the contingencies are not used.

We do not use the CNE available in the CRAC

Hvdc lines cannot not be selected because they are not branches, and we cannot compute their sensitivity.

The CNE are selected by running the provider on the reference network.
The selected CNE have to be available in the market-based network.
This means that the reference network can be a geographical subnetwork (Spain and France for example) of the market-based network (SWE).

Operational condition alignment

The operational conditions of the market-based network are aligned with those of the real time snapshot.
The preventive range actions of these operations are not respected.

This simple behavior might change later.

We assume that the IDs of each network element remains the same between the market-based network and the real time snapshot.

We create a pipeline with desired operational condition aligner.
Here are the available operational condition aligners:

Crac alignment

We apply each network action that has been applied to the real time snapshot to the market-based network.

We ignore the usage rules of the network actions. This means that not only preventive network actions will be used, but also curative ones

Matching HVDC mode and power

For each HVDC line on the market-based network, their mode and power are aligned with their corresponding HVDC line on the real time snapshot.
A warning is issued when some HVDC lines do not have any corresponding HVDC line on the other line.

An HVDC modeled with its AC representation (two generators and loads) will not be aligned.

PST alignment

For each PST on the market-based network, their tap is aligned with their corresponding PST on the real time snapshot.
A warning is issued when some PSTs do not have any corresponding PST on the other network.
Ratio tap PST and phase tap PST are aligned.

Branch connection state aligner

For each branch from the market-based network, the connection states of both terminals are aligned with the ones from the reference network. The algorithm checks if both terminals (through the voltage level ids) are the same in both networks (possibly mismatched).

Dangling line aligner

We want to align exchanges with countries that are not included in the reference network.

  • Given an unpaired reference dangling line,
    • If the market-based dangling line is also not paired, we align the market-based dangling line target P.
    • If the market-based dangling line has been paired, the market-based tie line will be unpaired, and we align the corresponding unpaired market-based dangling line target P.
  • Given a paired reference dangling line,
    • If the market-based dangling line is also paired, we ignore this dangling line.
    • If the market-based dangling line is not paired, we throw an issue.

Align inner exchanges

The goal is to align the exchanges of market-based network on the exchanges of the real time snapshot for each boundary of the real time snapshot.

With balances adjustment

The alignement can be done with balances adjustment, which is used for the SWE.
The alignment is ignored if the exchanges are already the same.

$c$ is a country in the market-based network.
$NP_{target}(c)$ is the target net position of a country $c$.
This net position will be the goal of the balance adjustment.
$exchange_{networkN}(countryA, countryB)$ defines the leaving flow from country $countryA$ to country $countryB$ in the network $networkN$.
If the country is not present in the real-time snapshot, the net position remains the same.
Otherwise, $$NP_{target}(c) = NP_{market} + \sum_{otherCountry!=c}exchange_{real-time}(c, otherCountry) - \sum_{otherCountry!=c}exchange_{market-based}(c, otherCountry)$$

This formula allows the alignement to be valid even with a real time network that might be a subpart of the market-based network.
If the networks have the same countries, this is equivalent to setting the target net positions to the real-time net positions.
If the network is not for a NTC process and if a smaller network is used, the alignement might fail with a status TARGET_NET_POSITION_REACHED_BUT_EXCHANGE_NOT_ALIGNED.

This simple bahavior might be changed in the futur is required. But it does not make sens from a métier point of view as the afrr concept exists.

With simple shifts

Another alternative for inner exchanges alignment is the use of a network shift, as done for the Italy North capacity calculation region.

In the Italy North region, the target is defined on the global Italian import from the four countries to the north. two input documents (NTC annual and NTC reductions) define how to split the generation increase among the four countries: they define splitting factors (between 0 and 1, with their sum equal to 1) to fix the share of each country (NB: Germany is included in the share of Switzerland).

Several iterations of shifts are run in order to reach the targeted Italian import value to take into account the losses (an increase of X MW of the generation in a given area does not mean that the exports from the area increase by exactly the same value).

The code calls a method called shiftNetwork from the external class LinearScaler: its inputs are the targeted value of Italian import (positive when Italy imports, opposite to the Italian net position) from the reference network, whereas the NTC values used for the computation are the ones from the market-based network.

HVDC AC modeling environment

If you need to transform your HVDC equivalent model to HVDC, we provide an environment.
When we enter the environment, the HVDC equivalent models are turned into HVDC.
Then a specified aligner is called (for example aligning exchanges).
Then the HVDC are turned into their equivalent models.
We do not keep HVDC in the network to be able to compute their PTDF.

Warning, if you have HVDC in DC mode, this environment might reset their set point !

Pipeline example

Here is an example of a pipeline

CracAligner cracAligner = new CracAligner(crac);
HvdcAligner hvdcAligner = new HvdcAligner();
PstAligner pstAligner = new PstAligner();
DanglingLineAligner danglingLineAligner = new DanglingLineAligner();
ExchangeAligner exchangeAligner = new ExchangeAligner(balanceComputationParameters, loadFlowRunner, computationManager, marketBasedScalable);
HvdcAcModelingEnvironment hvdcAcModelingEnvironment = new HvdcAcModelingEnvironment(creationParametersSet, exchangeAligner);
OperationalConditionAligner operationalConditionAligner = new OperationalConditionAlignerPipeline(cracAligner,
        hvdcAligner,
        pstAligner,
        danglingLineAligner,
        hvdcAcModelingEnvironment);

Flow extraction

For all selected lines, we can extract:

  • $P_{A,CC}(i)$ the AC power flow of line $i$ in the aligned market-based network
  • $P_{RT}(i)$ the AC power flow of line $i$ in the real time snapshot network

By default, we use the terminal 1 flow as power flow.

Sensitivity computation

For all selected lines, we can compute $PTDF(i)$ the zonal PTDF in the real time snapshot network with an AC sensitivity computation.

By default, we use the terminal 1 during the sensitivity analysis.

The HVDC are modeled with their equivalent model to be able to compute their zonal PTDF.

Therefore, HVDC saturations are ignored.

Uncertainties computation

The uncertainty of a given line $i$ is

$$UN(i)=\frac{P_{A,CC}(i)-P_{RT}(i)}{PTDF(i)}$$