docs: def extension (network, session, version, scn_extension, start_snapshot, 
                 end_snapshot, **kwargs):
      """
      Function that adds an additional network to the existing network container. 
      The new network can include every PyPSA-component (e.g. buses, lines, links). 
      To connect it to the existing network, transformers are needed. 
          
      All components and its timeseries of the additional scenario need to be inserted in the fitting 'model_draft.ego_grid_pf_hv_extension_' table. 
      The scn_name in the tables have to be labled with 'extension_' + scn_name (e.g. 'extension_nep2035').
  
      Until now, the tables include three additional scenarios:
      'nep2035_confirmed': all new lines and needed transformers planed in the 'Netzentwicklungsplan 2035' (NEP2035) that have been confirmed by the Bundesnetzagentur (BNetzA)
  
      'nep2035_b2': all new lines and needed transformers planned in the NEP 2035 in the scenario 2035 B2
  
      'BE_NO_NEP 2035': DC-lines and transformers to connect the upcomming electrical-neighbours Belgium and Norway 
       Generation, loads and its timeseries in Belgium and Norway for scenario 'NEP 2035'
  
  
       Parameters
       -----
            network : The existing network container (e.g. scenario 'NEP 2035')
            session : session-data
            overlay_scn_name : Name of the additional scenario (WITHOUT 'extension_')
            start_snapshot, end_snapshot: Simulation time
  
      Returns
      ------
            network : Network container including existing and additional network
  
      """
      
      if version is None:
         ormcls_prefix = 'EgoGridPfHvExtension'
      else:
          ormcls_prefix = 'EgoPfHvExtension'
                 
      # Adding overlay-network to existing network
      scenario = NetworkScenario(session,
                                 version = version,
                                 prefix=ormcls_prefix,
                                 method=kwargs.get('method', 'lopf'),
                                 start_snapshot=start_snapshot,
                                 end_snapshot=end_snapshot,
                                 scn_name='extension_' + scn_extension)
  
      network = scenario.build_network(network)
  
      # Allow lossless links to conduct bidirectional
      network.links.loc[network.links.efficiency == 1.0, 'p_min_pu'] = -1
  
      # Set coordinates for new buses
      extension_buses = network.buses[network.buses.scn_name ==
                                      'extension_' + scn_extension]
      for idx, row in extension_buses.iterrows():
              wkt_geom = to_shape(row['geom'])
              network.buses.loc[idx, 'x'] = wkt_geom.x
              network.buses.loc[idx, 'y'] = wkt_geom.y
                 
      return network