Re: [TCML] Paralleling differnt 14400 5KVA transformers, Fillament transformer progress.

[Bert Hickman <bert.hickman@xxxxxxxxxx>]

Jim,

Although there are ways to externally compensate for different 
transformer percent impedances (%Z), its simpler to select transformers 
that have the closest faceplate %Z ratings to more evenly share load 
current. When paralleled with a higher %X+Z transformer, a lower %Z 
transformer will supply a higher proportion of the total load current. 
Identical %Z transformers will equally share the load.

You can easily measure the degree of current sharing between pairs of 
transformers by paralleling the HV outputs, connecting individual 
ammeters in series with each LV winding, and then driving the pair 
through a common ballast inductor. From a practical standpoint, even 
moderate (~25%) imbalances should not create a major problem since 
distribution transformers have significant overload capability and you 
have a relatively low duty cycle application.

Because your new PT has a higher (5 kVA) rating than most PT's, it's 
most likely a Control Potential Transformer (CPT). These are sometimes 
used to provide low voltage control power within substations and not for 
voltage metering purposes. Even if it doesn't have a %Z rating on the 
faceplate, you can connect it in parallel with one of your distribution 
transformers (as above) and determine the degree of load sharing for sure.

Bert
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Jim Mora wrote:
> Hi All,
>
> My big coil (22" sono tube) is on the back burner but I am considering my
> various coil projects as a whole. As you all know by now it is hot as hell
> here and very dry! (So Ca) A good time to wind or at least coat water
> soakers... 
>
> I have a really nice, new 5KVA PT @14440. I also have a 5KVA pole pig. Both
> support 240v in. Just adding a second current control slide and stacking a
> 2nd voltage control 1256D will deliver ~14400va from my control cabinet.
>
> This is my ideal voltage/current for charging .2uf (2 ea paralleled, new
> .1uf GA 1000pps caps) to a .5 inch primary. Asrg will run btw 200 and
> 400BPS.
> Do you think this combination of transformers is ok? Otherwise I will need
> yet another 14400v at 10 or 15KVA (I have (3) 14400v 5kva units, one dry,
> one in the pole tank, and one nicely potted PT).
>
> Jim Mora
>
> PS The DIY filament transformer works great! I can deliver 50amps @ 10.4v
> (measured with 2 current clamps and a DVM for voltage) without breaking a
> sweat.
>
> I plan to add a few turn and add a 12v tap. I can tell where I unwound the
> #6awg (was 12v) before I cut it. I'll post a couple of pictures and document
> the turns when its done. My only wish is that I would have joined the France
> E cores before I wound the secondary; as there is almost 2" gap between the
> primary and secondary on the core. I guess I may need a weird tap in the
> future - lots of room! So save you dead 15/60 France Transformers. I bet the
> sign shops have lots with a good primaries for disposal since GFP. BTW the
> primary of the France I had was aluminum under the coating as are my MOTs. I
> bitch to solder if you don't move really fast after cleaning the aluminum.
>
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