I would like to design a transient protection solution for HVDC_pulse_unit.
HVDC voltage = 3500V , current > 40kA.
D1 flyback diode survives(50kA surge forward current).
MOVs section did not trigger (1200j, Varistor voltage = 5400V).
D4 12x low power serial diodes (300mA, 16kV each) rated 192kV burned.
EDIT:D4 is placed wrongly on the circuit. It protects the rectifier bridge of the charger inside the pulse unit. It was mentioned to acknowledge the magnitude of the voltage spike. Please ignore it.
Op1 - Using RC Snubber method for 3kA pulses (picture below), R C values where computed. The problem is voltage rating for C1. If D4, rated at 192kV failed how would a snubber capacitor survive?
Op2 - Would "normal" 1500W peak power TVS diodes survive until the varistors start to conduct? A small inductor in series with the TVS diode in order to limit the current rate of change?
Are the two solutions viable? If so, which one is better? I have no formal schooling in electronics, so all kind of errors might plague this post. Thank you.
EDIT: I did a few tests (below 10kA) using TVS, 10 bidirectional 1.5KE400CA in series. Breakdown voltage 400V per diode. Still got 8kV voltage spikes (picture below, x100000 attenuation)