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RE: 1350 KVA Current limiting

Original poster: "Terry Oxandale" <Toxandale@xxxxxxx>

Can you provide some nameplate information from the variac. 10KVA is a
large variac, obviously larger than what many of use consider large -
the Superior 1250 variac, which is only 7.8 KVA.


-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Monday, July 24, 2006 2:26 PM
To: tesla@xxxxxxxxxx
Subject: RE: 1350 KVA Current limiting

Original poster: "David Thomson" <dwt@xxxxxxxxxxxx>

Hi Bert,

Thanks for getting back so quick.

 > Original poster: Bert Hickman <bert.hickman@xxxxxxxxxx>
 > Tesla list wrote:
 > >  I knew the label said the transformers were rated for 450KVA

 > >each, but I thought I must be reading it wrong or a period was
 > >in front of the digits.  But it turns out that they really are
 > >for 450KVA and 5.5KV each.

 > Hi Dave,
 > What is the Staco model number? And, how much does each one
 > I strongly suspect that you actually have transformers rated
 > for 450 VA (0.450 kVA).

You are right.  I looked at the labels too quick.  The
transformers are rated to 450 VA, not KVA.

But my variac definitely says it is rated to 10 KVA.  So where is
my problem?  Why am I popping the fuses on the variac?

The transformers, BTW, are not Staco, but RAYCO.  They are 120V
50/60 Hz input.  I guess I don't understand the output.  The
diagram for the secondary shows one lead in and one lead out, but
the winding diagram has a gap in it.  These are not center tap
secondaries.  Also, the output lead is intended to be fused, but
I have bypassed the fuse since they are $50 each plus $20
shipping.  According to the wiring diagram, the fuse is entirely
in the output lead and not between windings. The label says it is
a 5.5KV transformer, the wiring diagram has "2400 V, 450 VA"
between the output leads.

It's hard to tell what the model number is, because there are so
many numbers on the label.  It does have an military NSN number
on it, as I bought these as military surplus.  The part that
might be the model number is X80-7407.  There is also a CAGE
number, and two more unidentified numbers.

I have all the primaries in parallel and the secondaries in

 > You can limit current to ANY sized transformer by adding
 > inductance in series with the LV side primary. This works
 > irrespective of the actual KVA rating of the transformer(s),
 > and is a simpler, safer, more efficient, and usually much
 > more cost effective way than trying to limit current on the HV

Thanks, I have a suitable ballast I can use.