Voltage monitoring

Contents

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

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 VoltageMonitoringResult run(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 = ...
VoltageMonitoringResult voltageMonitoringResult = new VoltageMonitoring(crac, network, raoResult).run("OpenLoadFlow", loadFlowParameters, 2);

The voltage monitoring result

The VoltageMonitoringResult object contains all the relevant results of the voltage monitoring algorithm.

JSON import & export

The VoltageMonitoringResult can be written to and read from a JSON file.
Example:

// Export
VoltageMonitoringResult voltageMonitoringResult = ...
OutputStream os = ...
new VoltageMonitoringResultExporter().export(voltageMonitoringResult, os);

// Import
InputStream is = ...
Crac crac = ...
VoltageMonitoringResult voltageMonitoringResult2 = new VoltageMonitoringResultImporter().importVoltageMonitoringResult(is, crac);

The VoltageMonitoringResult object contains the results of the voltage monitoring algorithm.

Status

The VoltageMonitoringResult has methods describing the security status of the network in regard to the voltage constraints defined in the CRAC:

SECURE: the network is secure; no voltage thresholds are violated
HIGH_VOLTAGE_CONSTRAINT: the network is not secure; at least one voltage CNEC has a voltage value higher than its threshold
LOW_VOLTAGE_CONSTRAINT: the network is not secure; at least one voltage CNEC has a voltage value lower than its threshold
HIGH_AND_LOW_VOLTAGE_CONSTRAINTS: the network is not secure; at least one voltage CNEC has a voltage value higher than its threshold, and at least one voltage CNEC has a voltage value lower than its threshold

// get the overall status (one of 4 values above)
public Status getStatus()

This information is not directly accessible in the JSON file.

Voltage values

The following methods return information about the voltage values for voltage CNECs.

// get VoltageCnecs that have a voltage overshoot
public Set<VoltageCnec> getConstrainedElements()

// get the minimum voltage value among all elements of a voltage CNEC, using the VoltageCnec object or its ID in the CRAC, in KILOVOLTS
public Double getMinVoltage(VoltageCnec voltageCnec)
public Double getMinVoltage(String voltageCnecId)

// get the maximum voltage value among all elements of a voltage CNEC, using the VoltageCnec object or its ID in the CRAC, in KILOVOLTS
public Double getMaxVoltage(VoltageCnec voltageCnec)
public Double getMaxVoltage(String voltageCnecId)

// get min/max voltage values for all voltage CNECs (ExtremeVoltageValues contain one min and one max value in KILOVOLTS)
public Map<VoltageCnec, ExtremeVoltageValues> getExtremeVoltageValues()

Example:

  "extreme-voltage-values-in-kilovolts" : [ {
    "cnec-id" : "VL45",
    "min" : 144.383355903481,
    "max" : 148.4102909359121
  }, {
    "cnec-id" : "VL46",
    "min" : 143.0995761393377,
    "max" : 147.66000723838806
  } ]

Printing the result

You can get a human-readable report of the voltage monitoring algorithm, using the following method of the VoltageMonitoringResult object:

public List<String> printConstraints()

Complete JSON example

{
  "type" : "VOLTAGE_MONITORING_RESULT",
  "extreme-voltage-values-in-kilovolts" : [ {
    "cnec-id" : "VL45",
    "min" : 144.383355903481,
    "max" : 148.4102909359121
  }, {
    "cnec-id" : "VL46",
    "min" : 143.0995761393377,
    "max" : 147.66000723838806
  } ]
}

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
From the CRAC, get the set of states on which VoltageCnecs exist
For each of these states, monitor voltages:
- Use a new copy of the network
- If the state is not preventive,
  - apply the contingency on the network
  - from the RaoResult, apply on the network the optimal remedial actions decided by the RAO (automatic and curative)
- Compute load-flow and fetch voltage values for all voltage CNECs
  - If the load-flow diverges move on to the next state
- Compare the voltages to their thresholds to report security status
  - SECURE: the network is secure; no voltage thresholds are violated
  - HIGH_VOLTAGE_CONSTRAINT: the network is not secure; at least one voltage CNEC has a voltage value higher than its threshold
  - LOW_VOLTAGE_CONSTRAINT: the network is not secure; at least one voltage CNEC has a voltage value lower than its threshold
  - HIGH_AND_LOW_VOLTAGE_CONSTRAINTS: the network is not secure; at least one voltage CNEC has a voltage value higher than its threshold, and at least one voltage CNEC has a voltage value lower than its threshold
- Create a [VoltageMonitoringResult]{#result} containing voltage values and security status
Assemble all the state-specific VoltageMonitoringResult in one overall VoltageMonitoringResult

Voltage monitoring algorithm