Dave,
Wow those commercial saturable reactors are beasts! I wonder if it would be
possible to build in current limiting into the pole pig itself (much like
an NST)? You could you add shims into the cores of the pig itself (of
course you loose real time adjustments on a running system). Or perhaps by
removing the pig's core and transplanting into a different case that had an
adjustment knob/wheel/lever to raise and lower the core would be better.
~Dan
On Wed, Jun 6, 2018 at 8:28 AM, Dave Leddon <dave@xxxxxxxxxx> wrote:
> I purchased an inexpensive arc welder from Sears which had a retractable
> transformer core to adjust the current. With the welder output shorted I
> could adjust the pole pig current from 18 to 60 amps.
>
> Dave
>
> At 07:21 PM 6/5/2018, you wrote:
>
>> Content-Transfer-Encoding: base64Dan,
>>
>> A shorted welding transformer stores energy in an expanding magnetic
>> field which is then returned to the power circuit as the sine wave of the
>> input power waveform decays, kinda like compressing a spring. When you
>> relieve the pressure on the spring, the spring pushes the energy back into
>> your system.
>>
>> If you use a resistor, the resistor converts the energy to heat, which is
>> lost, and not returned to the system. This is much less efficient. It
>> would provide ballasting, at the expense of a lot of waste heat. Any
>> resistance in the ballast components will generate waste heat, so you want
>> to minimize that as much as possible.
>>
>> If you want an easily and infinitely adjustable ballast, you would use a
>> saturable reactor. This is a special transformer which would perform the
>> same function as a shorted welder, but in which the permitted current is
>> controllable by a small low voltage DC current applied to a special set of
>> control windings.
>>
>> Saturable reactors provide nice control for TC systems, but ones big
>> enough to effectively control a pole pig can easily weigh half a ton, and
>> are usually very expensive, unless you can find a surplus unit for cheap.
>>
>> Last spring, I bought an assembly nearly identical to the following one
>> for $130 for the copper scrap value, but it cost me $580 in shipping fees
>> to get it to my friend's factory shipping dock. "Some day" I hope to build
>> a coil big enough to put it to effective use.
>>
>> https://www.ebay.com/itm/40-KVA-20-AMP-460-VOLT-HUNTERDON-SA
>> TURABLE-CORE-REACTOR-TRANSFORMER-S-1207-1/292572873068
>>
>> The reactor that was in it looks just like the following one, but is mine
>> "only" 52 KVA rated. I think there is a typo in the listing. The rating
>> should be more like 60 KVA, not 600. I would speculate that a 600 KVA core
>> would likely weigh several tons.
>>
>> https://www.ebay.com/itm/NEW-Hunterdon-Saturable-Core-Reacto
>> r-Transformer-600KVA-60Hz-WE-1097-R-C98R2/282780054079
>>
>> (I have no connection to either seller.)
>>
>> You can buy a lot of welders to short out for $4,800 plus shipping.
>>
>> To understand saturable reactors, look up "magnetic amplifiers" in
>> Wikipedia.
>>
>> Dave
>>
>>
>> On 6/5/2018 11:22 AM, Daniel Kunkel wrote:
>>
>>> As already pointed out, for a current limiting ballast transformer, the
>>> secondary coil will be shorted out, and the primary will be in series
>>> with
>>>
>> HØY‚€£â†÷vWfW"Â’†fR&VVâvöæFW ing what would happen if you put a (variable)
>>
>>> resistor on the secondary side of the ballast transformer (instead of a
>>> dead short). I wonder if this would give you some degree of variable
>>>
>> Ý\œ™[ [Z][™Âg&öÒÆÂ×’&VF ng, it seems like the best current
>> [Z][™È\Ù\È“Õ@nductance and resistance...so I wonder if resistance
>> Àcated in this location would work.
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