[TCML] DC resonant charging coil, rectifier protection

[Tuomas Koivurova <tkoivuro@xxxxxxxxx>]

Hello all.

I have 10kW (yes, kW, not kVA) DC spark gapper and so far i have
destroyed my rectifier twice.

First time i had DC feed wires running under RF grounded metal mesh
ang that mesh got hit by huge ground strike -> arc between mesh and
feed wire -> blown rectifier.

After this i added center tapped sagety gap to the coil end HV+ -> <-
RF ground -> <- HV-

This time i got few bangs and pops from the safety gap before my
rectifier failed again. First rectifier was 24kV 750mA and second one
was 50kV 6A. Im using 3 phase 10kVAC transformer so there should be
plenty of headroom.

My best guess is that both times this failure happened because of
common mode RF overvoltage getting back to my rectifier/transformer
(transformer case was tied to house ground). I have 30H charging
reactor in series with positive DC rail right next to rectifier at
transformer end of the transmission line. Both times it has been the
negative side diodes that got shorted.

For 3rd rectifier im planning to ground the negative side of HV DC
line to transformer case through 100nF-1µF capacitor and also have
similar capacitor between HV+ and HV-. Does this make sense? I tried
searching but there is not whole lot regarding DC coils.

Anyone got better ideas?
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