Voltage monitoring

Contents

Introduction
The Java API
The voltage monitoring result
The voltage monitoring algorithm
The output logs

Introduction #

In the FARAO CRAC, the user can define voltage constraints on network elements.
These are constraints that monitor that the voltage values on given network elements do not exceed a given threshold.
FARAO allows modelling these constraints in VoltageCnec objects.
However, modelling the impact of remedial actions on voltage values is highly complex and non-linear. This is why CASTOR does not inherently support voltage constraints.
The VoltageMonitoring package allows monitoring voltage values after a RAO has been run.

Voltage monitoring

The Java API #

You can easily call the voltage monitoring module using the JAVA API:

Build a VoltageMonitoring object using:
```
public VoltageMonitoring(Crac crac, Network network, RaoResult raoResult)
```
With:
- crac: the CRAC object used for the RAO, and containing VoltageCnecs to be monitored.
- network: the network to be monitored.
- raoResult: the RaoResult object containing selected remedial actions (that shall be applied on the network before monitoring voltage values)
Run the monitoring algorithm using the constructed object’s following method:
```
public RaoResult runAndUpdateRaoResult(String loadFlowProvider, LoadFlowParameters loadFlowParameters, int numberOfLoadFlowsInParallel)
```
With:
- loadFlowProvider: the name of the load-flow computer to use. This should refer to a PowSyBl load flow provider implementation
- loadFlowParameters: the PowSyBl LoadFlowParameters object to configure load-flow computation.
- numberOfLoadFlowsInParallel: the number of contingencies to monitor in parallel, allowing a maximum utilization of your computing resources (set it to your number of available CPUs).

Here is a complete example:

Crac crac = ...
Network network = ...
RaoResult raoResult = Rao.find(...).run(...)
LoadFlowParameters loadFlowParameters = ...
RaoResult raoResultWithVoltageMonitoring = new VoltageMonitoring(crac, network, raoResult).runAndUpdateRaoResult("OpenLoadFlow", loadFlowParameters, 2);

The voltage monitoring result #

The method presented above generates a new RAO result object, which is equivalent to the initial one, augmented by the relevant results of the angle monitoring algorithm :

The computation status of the RAO is updated
The voltage & margin values for voltage CNECs are updated
The activated network actions are updated

The voltage monitoring algorithm #

Here is a detailed description of how the voltage monitoring algorithm operates:

Apply optimal preventive remedial actions from RaoResult on the network
For each of these states, monitor voltages:
From the CRAC, get the set of states on which VoltageCnecs exist
(A) For each of these states, generate a state-specific VoltageMonitoringResult:
- If one of these states is the preventive state, deal with it before handling any of the contingency states. Directly work on the input network. That way, applied voltage preventive remedial actions will be taken into account in the contingency states. Go to (B)
- Else, for all contingency states :
  - Use a new variant of the network
  - apply the contingency on the network
  - From the RaoResult, apply on the network the optimal remedial actions decided by the RAO (ARA+CRA, given PRAs have already been applied). Go to (B).
- (B) Compute the LoadFlow
  - If it diverges, return a VoltageMonitoringResult with the following content for this state, then move on to the next state:
    - the voltages of the VoltageCnecs equal to NaN
    - no applied remedial actions
    - security status UNKNOWN
- Compute the voltages for all VoltageCnecs (computeVoltages method)
- Compare the voltages to their thresholds. For the VoltageCnecs that have a voltage overshoot, get the associated remedial actions (with an OnVoltageConstraint usage rule containing the VoltageCnec and the state’s instant)
  - If the VoltageCnec has no associated RA, log a warning that the voltage constraint cannot be remedied, and move on to the next VoltageCnec.
  - For every RA:
    - If the remedial action is not a network action, do not apply it and log a warning. Then move on to the next RA.
    - If the RA is a network action, apply it on the network
- If you applied any RA, recompute the LoadFlow
  - If it diverges, return a VoltageMonitoringResult with the following content for this state, then move on to the next state:
    - the voltages of the VoltageCnecs equal to what was computed before RA application
    - no applied remedial actions
    - security UNSECURE (variant of HIGH/LOW_VOLTAGE_CONSTRAINT)
- Re-compute all voltage values
- Create a state-specific voltage monitoring result with voltages, list of applied remedial actions , and secure flag set to SECURE if there is no more overshoot (after re-verifying thresholds)
- Move on to next state (Go to (A)).
Assemble all the state-specific results in one overall result, and update the RAO result object

Voltage monitoring algorithm

The output logs #

In the logs, the start and end of different steps are logged:

Start and end of the voltage monitoring algorithm
Start and end of the monitoring of each state (preventive or post-contingency)
Start and end of each load-flow computation

Also, the following information is logged:

Applied remedial actions to relieve voltage constraints
At the end of each state monitoring, the list of remaining voltage constraints
At the end of the monitoring algorithm, the list of remaining voltage constraints

Example 1:
In this example, a constraint exists in preventive (it cannot be solved because FARAO cannot implement PRAs to solve voltage constraints), and another one in curative (but implementing the CRA does not solve it).

INFO  c.f.f.commons.logs.RaoBusinessLogs - ----- Voltage monitoring [start]
INFO  c.f.f.commons.logs.RaoBusinessLogs - -- Monitoring voltages at state "preventive" [start]
INFO  c.f.farao.commons.logs.TechnicalLogs - Load-flow computation [start]
INFO  c.f.farao.commons.logs.TechnicalLogs - Load-flow computation [end]
WARN  c.f.f.commons.logs.RaoBusinessWarns - VoltageCnec vcPrev is constrained in preventive state, it cannot be secured.
INFO  c.f.f.commons.logs.RaoBusinessLogs - Some voltage CNECs are not secure:
INFO  c.f.f.commons.logs.RaoBusinessLogs - Network element VL1 at state preventive has a voltage of 400 - 400 kV.
INFO  c.f.f.commons.logs.RaoBusinessLogs - -- Monitoring voltages at state "preventive" [end]
INFO  c.f.farao.commons.logs.TechnicalLogs - Using base network 'phaseShifter' on variant 'InitialState'
INFO  c.f.f.commons.logs.RaoBusinessLogs - -- Monitoring voltages at state "co - curative" [start]
INFO  c.f.farao.commons.logs.TechnicalLogs - Load-flow computation [start]
INFO  c.f.farao.commons.logs.TechnicalLogs - Load-flow computation [end]
INFO  c.f.f.commons.logs.RaoBusinessLogs - Applying the following remedial action(s) in order to reduce constraints on CNEC "vc": Open L1 - 2
INFO  c.f.farao.commons.logs.TechnicalLogs - Load-flow computation [start]
INFO  c.f.farao.commons.logs.TechnicalLogs - Load-flow computation [end]
INFO  c.f.f.commons.logs.RaoBusinessLogs - Some voltage CNECs are not secure:
INFO  c.f.f.commons.logs.RaoBusinessLogs - Network element VL1 at state co - curative has a voltage of 400 - 400 kV.
INFO  c.f.f.commons.logs.RaoBusinessLogs - -- Monitoring voltages at state "co - curative" [end]
INFO  c.f.f.commons.logs.RaoBusinessLogs - Some voltage CNECs are not secure:
INFO  c.f.f.commons.logs.RaoBusinessLogs - Network element VL1 at state co - curative has a voltage of 400 - 400 kV.
INFO  c.f.f.commons.logs.RaoBusinessLogs - Network element VL1 at state preventive has a voltage of 400 - 400 kV.
INFO  c.f.f.commons.logs.RaoBusinessLogs - ----- Voltage monitoring [end]

Example 2:
In this example, a curative constraint (after contingency “co”) is solved by a CRA.

INFO  c.f.f.commons.logs.RaoBusinessLogs - ----- Voltage monitoring [start]
INFO  c.f.farao.commons.logs.TechnicalLogs - Using base network 'phaseShifter' on variant 'InitialState'
INFO  c.f.f.commons.logs.RaoBusinessLogs - -- Monitoring voltages at state "co - curative" [start]
INFO  c.f.farao.commons.logs.TechnicalLogs - Load-flow computation [start]
INFO  c.f.farao.commons.logs.TechnicalLogs - Load-flow computation [end]
INFO  c.f.f.commons.logs.RaoBusinessLogs - Applying the following remedial action(s) in order to reduce constraints on CNEC "vc": Close L1 - 1
INFO  c.f.farao.commons.logs.TechnicalLogs - Load-flow computation [start]
INFO  c.f.farao.commons.logs.TechnicalLogs - Load-flow computation [end]
INFO  c.f.f.commons.logs.RaoBusinessLogs - All voltage CNECs are secure.
INFO  c.f.f.commons.logs.RaoBusinessLogs - -- Monitoring voltages at state "co - curative" [end]
INFO  c.f.f.commons.logs.RaoBusinessLogs - All voltage CNECs are secure.
INFO  c.f.f.commons.logs.RaoBusinessLogs - ----- Voltage monitoring [end]