Original poster: "Gerry Reynolds" <gerryreynolds@xxxxxxxxxxxxx> Hi Ed,This could indeed be the cause. When I was first turning on my SRSG, I ran into ferroresonance. I removed the SRSG and the NST's were only driving the Cp. I scoped the NST output as the variac was being brought up. Everyting stayed sorta linear until I hit 90Vac. At this point, the output snapped to 29KV (about the voltage the MOVs summed up to) and the PF went to 1.0 indicating resonance. It could be that the same is happening with a static gap set for the maximum NST output with full variac input voltage. With the variac at some lower voltage, the output probably doesn't get high enough to fire the gap until ferroresonance occurs. I have never experimented with this with a Cp of 1.6*Cres, only with 2.6*Cres.
Gerry R.
Original poster: Ed Phillips <evp@xxxxxxxxxxx> Hi Gary,I agree to not let our guard down with LTR. I suspect that when the variac is slowly cranked up, transients are still being introduced although they are probably less than when the power is applied all at once.Gerry R"The leakage reactance of the transformer varies with input voltage and hence the flux density in the core and, with the right secondary capacitor, it's possible to get a condition in which a ferroresonance occurs and the voltage soars dramatically, perhaps to breakdown levels.First time I ran into this I blew up a Simpson 260 on the 5 kV scale. Ed