Current Limiting

From:  Esondrmn-at-aol-dot-com [SMTP:Esondrmn-at-aol-dot-com]
Sent:  Friday, January 30, 1998 1:08 PM
To:  tesla-at-pupman-dot-com
Subject:  Re: Current Limiting

In a message dated 98-01-30 00:59:54 EST, you write:

 I was thinking this morning about current limiting.. [I still dream of 
 the day I can get that Pig... and want to be ready] I thought of
 something that is a) very simple, and b) probably does not work.
 So someone tell me why please :)
 Since I am mostly a software kinda guy, with a smattering of digital
 design, dealing with this high-power AC stuff always confuses me.
 If I understand it correctly - the idea behind reactive or resistive
 loads is to place an IR drop in series with the pig, such that when
 the current reaches a certain point, the IR loss prevents it from
 rising further [I know, the wording sucks, but the idea is 
 clear, I hope]
 So.. based on this idea.. and the fact that lightbulbs don't exactly
 short things out, why not use lightbulbs as resistive ballast?
 I am not exactly sure what the VA rating for a bulb is.. but for
 grins sake, assume a 100W bulb is 100VA, paralleling 2 bulbs gives
 you total power flow of 200VA, 3.. etc. [ for 220, use 2 110V bulbs in 
 Power control is two fold: Voltage via variac, and current by switching
 in more or less bulbs in series. 
- snip -


Your approach will certainly work as well as using heater cores, oven elements
and other resistive elements.  However, it is not an ideal solution.  Resitive
ballast will drop quite a bit of voltage across it and lower the voltage
available to the primary of the HV transformer.  Using reactive ballast such
as a variable inductor will also drop some voltage across it because if its
internal resistance but not nearly as much as a resistive ballast.

Ed Sonderman