diff --git a/edisgo/flex_opt/costs.py b/edisgo/flex_opt/costs.py
index d1aa910d..2079eb77 100644
--- a/edisgo/flex_opt/costs.py
+++ b/edisgo/flex_opt/costs.py
@@ -108,6 +108,7 @@ def _get_line_costs(lines_added):
     if not equipment_changes.empty:
         transformers = equipment_changes[
             equipment_changes.equipment.str.contains("Transformer")
+            | equipment_changes.equipment.str.contains("transformer")
         ]
         added_transformers = transformers[transformers["change"] == "added"]
         removed_transformers = transformers[transformers["change"] == "removed"]