[TCML] Paralleling NSTs

[Ed Phillips]

Hi Phillip,

Unlike distribution transformers, plate transformers, or even MOTS, you 
can indeed parallel NST's since they're sufficiently shunted to prevent 
dangerous levels of circulating currents even when open circuit voltages 
are substantially different. They'll happily play together when phased 
properly. Because there are circulating currents between the 15 kV and 
12 kV NST's, the combined open circuit output voltage of the hybrid 
combination will lie somewhere between that of a 12 kV and a 15 kV NST. 
And, since you'll be clamping the maximum voltage via your gap, this 
should not add any undue stress across the insulation of the 12 kV NST. 
While not as efficient as using NST' of the same voltage, this approach 
will indeed work... with NST's or OBIT's.

Bert"

    I'll add to that.  I've run a 9 kV, 60 ma transformer in parallel 
with a 12 kV, 60 ma and had no problems whatsoever.  When the gap fires 
the voltage across it drops to near zero and the capacitors recharge.  
Current through both transformers will be the same near short circuit 
but, if the gap is set wide enough, in addition to current charging the 
capacitor current will flow from the higher voltage unit into the 
smaller when the voltage exceeds its open circuit value.  So what?  
Everything is current limited [IF you have the safety gap to prevent 
series resonance].

Ed