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Re: current limiting on pole transformers


From: 	Bert Hickman[SMTP:bert.hickman-at-aquila-dot-com]
Reply To: 	bert.hickman-at-aquila-dot-com
Sent: 	Thursday, July 24, 1997 8:58 AM
To: 	Tesla List
Subject: 	Re: current limiting on pole transformers

Tesla List wrote:
> 
> From:   Rodney Stapivic[SMTP:rstapivic-at-sprynet-dot-com]
> Reply To:       rstapivic-at-sprynet-dot-com
> Sent:   Wednesday, July 23, 1997 6:57 PM
> To:     tesla-at-pupman-dot-com
> Subject:        current limiting on pole transformers
> 
> I have recently purchased a 14.4kv, 10kva single phase pole transformer for
> a good price. I understand current-limiting due to working with high power
> radar systems for a defense contractor, but my question is why under-
> saturate the 240v side? the transformer I bought is rated  at 42 amps max
> on the 240v side if used as an input. According to the specs from the
> manufacturer this is the max current it will draw when fully saterated. If
> I hook this one up to a 60 amp service and somewhere get a 50 amp or more
> 240v variac (does anyone have one for sale or a source?) I should not have
> a problem I would think. I'm trying to get away from welders, convection
> ovens, and I really don't want to use neon sign transformers. Any help is
> appreciated
> 
> thanks
> Rodney

Rodney,

Transformer core saturation does NOT limit primary current - quite the
opposite! Once you saturate the transformer, your primary current rises
dramatically, irrespective of the secondary load. If you don't have some
type of external current limiting in series with the primary, it can
easily draw more current than the total rated electrical service can
supply to your house. BTW, a similar thing will occur when you short
circuit the secondary with a spark gap - running with no ballast will
result in you drawing HUGE amounts of primary current - you could
literally "take down the neighborhood" with one of these if your supply
mains circuit breakers failed to open quickly enough! If you're gonna'
run a pig, you NEED a ballast of some sort. 

-- Bert --