add 3ph to rx min max for ext grid

Author: heckstrahler

pandapower/network_schema/ext_grid.py

@@ -42,15 +42,15 @@
         nullable=True,
         required=False,
         description="maxium R/X ratio of short-circuit impedance",
-        metadata={"sc": True},
+        metadata={"sc": True, "3ph": True},
     ),
     "rx_min": pa.Column(
         float,
         pa.Check.ge(0),
         nullable=True,
         required=False,
         description="minimum R/X ratio of short-circuit impedance",
-        metadata={"sc": True},
+        metadata={"sc": True, "3ph": True},
     ),
     "r0x0_max": pa.Column(
         float,