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Re: New Coil

Original poster: "Gerald  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Mike,

There is still a way to get excessive voltages even at 3x resonance. If the timing of the SRSG is too late after peak, the firing could stop and the NST could ferroresonate with Cp. The NST saturates and the current limiting inductance decreases. This in tern raises the resonant frequency back toward 60 Hz and saturates the NST more (unstable situation). End result is an NST that resonates with the Cp at 60Hz and voltages go sky rocketing unless something limits the rise (terry's filter with MOV's or a properly set safety gap).

Another possiblility, I'm wondering, is if the failure is peak current related. Since you have only one cap, it must take all the current in the primary. If you have the primary inductance value (like from JAVATC or some other program) you could calculate the peak current:

Imax = Vmax / sqrt(Lp/Cp)

Gerry R

Original poster: "Mike" <mike.marcum@xxxxxxxxxxxx>

It was a single 15/60 with a sync rotary (spacing between stationary and moving electrodes was close to 1/16" on each side (minus the play in the motor) and 120v in from a 0-120 variac. It was a single cap, so it was almost 3x resonant value (going by the geek group chart at the time). I have a 2nd one that failed in single mode (can't remember if I was using a 15 kv nst or a tougher 14.4 kV PT as this was a couple years ago), that simply cracked the case instead of guts and oil all over, but I'll be dissecting it this weekend.