Calculating RC Snubber circuit values

[Abednego Salmane]

I need help on designing/calculation snubber circuit for traction rectifier (3kV DC Substation)

Diode requirements/Rectifier requirements:

total number of diodes/ thyristors :24

number of diodes/ thyristors per arm:2 (in series)

type of diode/ thyristor:Lamina S.A. DB3-4000-45

max. repetitive reverse voltage of diode U RRM:4500V