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://www.roneverhart.com/HGST-Ultrastar-7K6000-HUS726040ALS214-4TB-7-2K-RPM-SAS-12Gb-s-512n-128MB-3-5-SE-Hard-Drive/