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


Why parallel transformers? We're talking about pigs here; they will do 10x
their name plate for several minutes with even getting warm. How much total
power are you going to run?


On Tue, Sep 1, 2009 at 8:59 AM, Bert Hickman <bert.hickman@xxxxxxxxxx>wrote:

> 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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