Throw exception if the slack node is not directly conected to a transformer.

CHANGELOG.md

@@ -43,6 +43,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Create `CITATION.cff` [#1035](https://github.com/ie3-institute/simona/issues/1035)
 - Introduce ThermalDemandWrapper [#1049](https://github.com/ie3-institute/simona/issues/1049)
 - Added Marius Staudt to list of reviewers [#1057](https://github.com/ie3-institute/simona/issues/1057)
+- Throw exception if the slack node is not directly conected to a transformer. [#525](https://github.com/ie3-institute/simona/issues/525)
 
 ### Changed
 - Adapted to changed data source in PSDM [#435](https://github.com/ie3-institute/simona/issues/435)

src/main/scala/edu/ie3/simona/io/grid/GridProvider.scala

@@ -7,6 +7,7 @@
 package edu.ie3.simona.io.grid
 
 import com.typesafe.scalalogging.LazyLogging
+import edu.ie3.datamodel.exceptions.{InvalidGridException, SourceException}
 import edu.ie3.datamodel.io.naming.FileNamingStrategy
 import edu.ie3.datamodel.io.source.csv.{
   CsvJointGridContainerSource,
@@ -51,6 +52,27 @@ object GridProvider extends LazyLogging {
             // checks the grid container and throws exception if there is an error
             ValidationUtils.check(jointGridContainer)
 
+            // check slack node location
+            val slackSubGrid = jointGridContainer.getSubGridTopologyGraph
+              .vertexSet()
+              .asScala
+              .filter(_.getRawGrid.getNodes.asScala.exists(_.isSlack))
+              .maxByOption(
+                _.getPredominantVoltageLevel.getNominalVoltage.getValue
+                  .doubleValue()
+              )
+              .getOrElse(
+                throw new InvalidGridException(
+                  "There is no slack node present in the grid."
+                )
+              )
+
+            if (slackSubGrid.getRawGrid.getNodes.size() > 1) {
+              throw new SourceException(
+                "There are too many nodes in the slack grid. This is currently not support."
+              )
+            }
+
             jointGridContainer
           case None =>
             throw new RuntimeException(