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Re: Test question

It was written:

>Test 1:
>3.08 VAC on X1 and X2 (input) 120-0 leads
>370 VAC on high voltage bushings (output)
>120:1 ratio approxomatly
>Therefore: 240 VAC in, 28800 out
>
>I know the output current would be reduced, but would the KVA rating 
>be halved?  I'm thinking it would be since you are now using one set 
>of windings on the primary.

Depends on what is really limiting the KVA.  If it is the heat 
dissipation rate of the core - then (ignoring primary winding I^2R 
losses) you would still be permitted the full KVA rating.

If you really wanted to get efficient you could rephase the other 
primary winding in parallel with the first.  That way you could run 
fully efficient 120 to 14400 conversion with minimal copper loss.

BUT - if you are planning on applying 240v to the 120-0 inputs leads - 
be warned this will drive the core into saturation - meaning that it'll 
draw a huge input current w/o a corresponding increase in output 
current.

We have overvolted our 25KVA pig up to about 350 volts on the 240 
terminals, and the currents starts getting huge right around there...

>Test 2:
>3.00 VAC on X1 and X2 (input) 120-120 leads
>neutral being disconnected from output lug and connected together
>180.0 VAC out
>60:1 ratio (this is what I expected)
>Therefore: 240 VAC in, 14400 out
>
>My question is, even though the skematic diagram on the nameplate 
>shows that the two primary leads are connected together to form the 
>X2, why is it that there is no output until the two leads are 
>disconnected from the X2 and left connected together?

You are using a pig of some sort, right?

Both pigs I've had apart have had four input (low voltage) busses 
connecting to two separate primaries.

In my experience the schematic tells the linesman how to connect these 
four internal busses for a given operation.  Our 25KVA pig came with one 
of the low voltage lugs disconnected from the internal windings.  We had 
to reconnect and rephase one of the windings to get it to work on 240V.

So - if you don't connect those two internal primaries in series for 
240v operation - no current can flow hence no output.

I hope I understood your problem correctly!

-Bill


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