we are in cane sugar plant, have 08 no. AC drive of ABB type ACS800-07 (1.2 MW, 1 MW & 630 KW). these are installed in 02 in 2006, 04 in 2008 & 02 installed in 2010. when we restart the drives after 8 month shutdown, the drive which are installed in 2006 & 2008, goes to fault INV SC. we check out in detail. all IGBT (FS450R12KE3/AGDR-71C) of all Out put Module are faulty. the problem is in Driver card (AGDR-62C & AGDR-71CS). the power Module is OK. any one help us? what is the case of fault and in future how we can take preventive actions?