The symmetrical bipolar configuration shows a great advantage in modular multilevel converter (MMC) based high-voltage dc-current (HVDC) transmission. In a bipolar MMC-HVDC system. station internal ac grounding faults cause sub-module (SM) capacitors to discharge violently. These faults do great harm to MMCs and require special protection schemes. https://allfixelectricales.shop/product-category/dryer-door-seal/