XC affect on BALLAST current.

["Tesla list" <tesla@xxxxxxxxxx>]

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

Hi All,

This issue has come up recently about the affect Cp has on the 
limiting current of a ballasted PIG.  I just finished my toroid 
ballast and measured its limiting current to be 17 amps (on the 
largest 245 turn tap) with a 280V variace driving it (calculates out 
to 44mh).  It took a much wider gap than expected to get the current 
up to this level but that is another story.  I was thinking I would 
have to reduce the number of turns from 245 to a lower number to get 
the desired 25 amps.  I have three taps on the toroid to get 25, 30, 
and 35 amps.

Tonight, I ran spice to see what effect driving the main Cp had on 
this current limit.  First, I simulated the PIG (turns ratio of 60) 
driving just the Cp (2.9*Cres or 130nf) with no SRSG connected.  This 
raised the current draw to 28.8 amps.  Next, I connected the SRSG 
modeled for 120 BPS with the LTR Cp and the current draw went up to 30 amps.

In the SRSG model, the timing was adjusted for maximum firing voltage 
(24.4KV).  The PIG output (HV side) was modeled with a 16800Vrms 
generator, a 158 h source inductor, and a 700 ohm source 
resistance.  These parameters reflect driving the PIG with 280Vac, 
transfering the ballast inductance to the PIGs HV side, and both the 
LV and HV winding resistance (LV resistance transfered to the HV side).

Based on the simulations, I think it would be prudent to account for 
the reactance of the Cp load (transfered to the LV side) when 
designing your ballast limits.  The extra boost in current, I 
believe, caused by after peak firing of the SRSG appears to not be as 
significant as the Cp load affect.

Gerry R.