IGBTs explosion in simovert multiparallel inverter

Dear Sir

We have two inverters units installed in Mecca dredger since 2004 with the following data:
• Multiparallel Simovert Master Drive, 700 V line voltage, 50 Hz, 3.4 MW
• 4-panel AFE rectifier and 4-panel Inverter
• Total installed IGBT are 96 units/unit (12 per panel),
• IGBT type FZ1200R16KF4S1
• Part number 6SE7038-6WK86-3DE0
6SE7038-6WK86-4DE0

These inverters drive two dredge pumps. The Mecca DPs drives frequent faults, which appears random and sometimes end without a clear reasons identifications, for example:

1. Some faults appeared in a certain panel and after fixing the fault, the same fault appeared again in another panel.
2. The IGBTs exploded without operation of the power protection fuses and the controller protection system.

The IGBTs explosions destroy the IGDs cards attached to the exploding IGBTs. Also, the snubber cards (if it found), the wide and the flat resistances may be burnt. The IGBTs explosions are increased noticeably (2011). The frequent faults lead to the following results:

1. Stop the DPs for several hours and sometimes days so, the dredger production decreased.
2. Consuming a lot of spare parts including electronic cards, IGBTs, flat and wide resistances. Sometimes some of these spare parts were changed and it was OK.

Kindely, can anybody give help about the reason of this explosion

i read some posts about increasing the igbts rate to FZ 1600..
or it may be from optical fiber or humidity, please i need help i have full report about this problem
if anyone need more information

dr alaa abozaid
suez canal authority