allow import from PowerFactory with VSC as slack (#2216)

CHANGELOG.rst

@@ -45,6 +45,7 @@ Change Log
 - [FIXED] avoid attaching elements as duplicates to a group where some of the elements already exist
 - [ADDED] the function :code:`run_contingency` can raise a captured error if parameter :code:`raise_errors` is passed
 - [FIXED] bugfix for tap dependent impedance characteristics so that not all characteristics columns are necessary
+- [FIXED] in function :code:`toolbox.replace_zero_branches_with_switches`, use absolute for the parameters of impedance elements in case they are negative nonzero values
 
 [2.13.1] - 2023-05-12
 -------------------------------

pandapower/toolbox/grid_modification.py

@@ -977,10 +977,11 @@ def replace_zero_branches_with_switches(net, elements=('line', 'impedance'), zer
                                             ].index.tolist())
 
         if elm == 'impedance' and zero_impedance:
-            branch_zero.update(net[elm].loc[(net[elm].rft_pu <= min_rft_pu) &
-                                            (net[elm].xft_pu <= min_xft_pu) &
-                                            (net[elm].rtf_pu <= min_rtf_pu) &
-                                            (net[elm].xtf_pu <= min_xtf_pu)].index.tolist())
+            # using np.abs() here because the impedance parameters can have negative values e.g. after grid reduction:
+            branch_zero.update(net[elm].loc[(np.abs(net[elm].rft_pu) <= min_rft_pu) &
+                                            (np.abs(net[elm].xft_pu) <= min_xft_pu) &
+                                            (np.abs(net[elm].rtf_pu) <= min_rtf_pu) &
+                                            (np.abs(net[elm].xtf_pu) <= min_xtf_pu)].index.tolist())
 
         affected_elements = set()
         for b in branch_zero: