Thyristor burnt at power failure

Dear Friends,

we have the 6RA8075-6DV62-0AA0-Z DC Drive. but since installation the drive has failure three times, and every time the thyristor burnt, and this happens at power failure. it happens like machine running well but if there will any power failure than the drive thyristor burnt. three times this had happen. cause is same while power failure than only the thyristor fails.   

we have placed the MCCB, SITOR Fuses, Choke, Power Contactor, in input side, and for output there are also fuses available for and short circuit or other issues, but fuses find healthy at all the time but thyristor burnt at power failure. this happens at any interval.

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Split from Thyristor protection.

Hello,

Could you please provide motor nameplate details? What is the application of DC motor? In lathe or Live tool spindle application? Are you providing SITOR fuses as per Siemens recomandetation? Is their SCVS at supply input side?

Does your machine has main incoming MCCB with U/V coil?

Please check above points.

Hello,

I have also faced this issue twice after electricity interrupt. Although the fuses at the input were blown, they were not aR type so the thyristors damaged. The first time at the upper bridge and the second at the lower, always the two same phases. It is about an extruder so the rotation is always towards one side. Is there any reasonable explanation? A gating problem probably?