Graph refiner

A preliminary step is done inside the GraphRefiner class. It performs some preprocessing on the input graph by calling several methods:

• An optional call to Graph.substituteInternalMiddle2wtByEquipmentNodes() to simplify the graph by substituting each internal two-winding transformers (i.e. both ends are in the same voltage level) FeederNode by a EquipmentNode, to avoid unnecessary snake lines;

• A systematic call to GraphRefiner::handleConnectedComponents which ensures that each connected component contains a BusNode: it is adding one if there is none;

• A systematic call to Graph.substituteFictitiousNodesMirroringBusNodes() to simplify the graph by removing FICTITIOUS nodes which are the only adjacent node of a BusNode;

• An optional call to Graph.removeUnnecessaryConnectivityNodes() to simplify the graph by removing redundant FICTITIOUS nodes;

• An optional call to Graph.substituteSingularFictitiousByFeederNode() to simplify the graph by replacing internal nodes with only one neighbor with a fictitious feeder node;

• An optional call to Graph.removeFictitiousSwitchNode() to simplify the graph by removing the fictitious switch nodes;

• A systematic call to Graph.extendBusesConnectedToBuses() to add 2 connectivity nodes between 2 buses that are connected to each other;

• A systematic call to Graph.insertBusConnections to create a connection between a bus node and its adjacent nodes;

• A systematic call to Graph.insertHookNodesAtBuses() to TODO

• A systematic call to Graph.insertHookNodesAtFeeders() to TODO

• A systematic call to Graph.substituteNodesMirroringGroundDisconnectionComponent() to deal with ground disconnector displaying.