Fix Infinite and NaN flowTransfer in security analysis results (#1367)

Signed-off-by: Damien Jeandemange <damien.jeandemange@artelys.com>

Author: jeandemanged

src/main/java/com/powsybl/openloadflow/network/impl/AbstractImpedantLfBranch.java

@@ -26,6 +26,8 @@
  */
 public abstract class AbstractImpedantLfBranch extends AbstractLfBranch {
 
+    private static final double P_EPSILON_SI = 1e-6; // in MW
+
     protected boolean connectedSide1;
 
     protected boolean connectedSide2;
@@ -520,7 +522,12 @@ protected BranchResult buildBranchResult(LoadFlowModel loadFlowModel, Map<String
 
         double flowTransfer = Double.NaN;
         if (!Double.isNaN(preContingencyBranchP1) && !Double.isNaN(preContingencyBranchOfContingencyP1)) {
-            flowTransfer = (flowP1 - preContingencyBranchP1) / preContingencyBranchOfContingencyP1;
+            double flowChange = flowP1 - preContingencyBranchP1;
+            if (Math.abs(preContingencyBranchOfContingencyP1) > P_EPSILON_SI) {
+                flowTransfer = flowChange / preContingencyBranchOfContingencyP1;
+            } else {
+                flowTransfer = 0.;
+            }
         }
         return new BranchResult(getId(), flowP1, flowQ1, currentI1, flowP2, flowQ2, currentI2, flowTransfer);
     }

src/test/java/com/powsybl/openloadflow/sa/OpenSecurityAnalysisTest.java

@@ -4931,7 +4931,7 @@ void testSaResultsWithZeroImpedanceModeAndT3wt() {
             false, TWO,  0.336
             true,  TWO,  0.333
         """)
-    void testContingencyDisconnectingZeroImpedanteBranchConnectedOneSide(boolean dc, TwoSides side, double expectedL12P1) {
+    void testContingencyDisconnectingZeroImpedanceBranchConnectedOneSide(boolean dc, TwoSides side, double expectedL12P1) {
         Network network = FourBusNetworkFactory.create();
 
         LoadFlowParameters loadFlowParameters = new LoadFlowParameters()
@@ -4952,4 +4952,27 @@ void testContingencyDisconnectingZeroImpedanteBranchConnectedOneSide(boolean dc,
         assertEquals(expectedL12P1, result.getPreContingencyResult().getNetworkResult().getBranchResult("l12").getP1(), DELTA_POWER);
         assertEquals(expectedL12P1, result.getPostContingencyResults().getFirst().getNetworkResult().getBranchResult("l12").getP1(), DELTA_POWER);
     }
+
+    @ParameterizedTest(name = "DC = {0}")
+    @ValueSource(booleans = {false, true})
+    void testZeroFlowTransfer(boolean dc) {
+        Network network = FourBusNetworkFactory.create();
+
+        LoadFlowParameters loadFlowParameters = new LoadFlowParameters()
+                .setDc(dc);
+        OpenLoadFlowParameters.create(loadFlowParameters);
+
+        // disconnect l14 on side 2, used as contingency
+        Line l14 = network.getLine("l14");
+        l14.getTerminal2().disconnect();
+
+        List<Contingency> contingencies = List.of(Contingency.line("l14"));
+        List<StateMonitor> monitors = createAllBranchesMonitors(network);
+
+        SecurityAnalysisResult result = runSecurityAnalysis(network, contingencies, monitors, loadFlowParameters);
+        NetworkResult networkResult = result.getPostContingencyResults().getFirst().getNetworkResult();
+        assertEquals(4, networkResult.getBranchResults().size());
+        networkResult.getBranchResults()
+            .forEach(br -> assertEquals(0., br.getFlowTransfer(), DELTA_POWER));
+    }
 }