smallest transformer

What is about the smallest size (in terms of physical dimensions) that a transformer could be made suitable to step 7200 volts down to 240 volts
in utility grade service, including any cooling parts as might be needed? Assume a very small load is all that needs to be powered, such as 50 VA or less. I'm presuming the necessary primary insulation is going to be the major factor limiting how small this can get. The secondary needs to be grounded, so floating service is not an option (and hence voltage to the enclosing case is an issue).
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I would assume such a transformer would be around the size of a television's horizontal output transformer. A bit bigger and heavier because of the frequency of the power being converted. Only 50VA would not require any special cooling system. You didn't mean 50KVA did you? John


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| I would assume such a transformer would be around the size of a television's | horizontal output transformer. A bit bigger and heavier because of the | frequency of the power being converted. Only 50VA would not require any | special cooling system. You didn't mean 50KVA did you?
No, I did not mean 50kVA, just 50VA ... enough to power a small light.
But a 7200->240 one would be larger than a 120->12 one.
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On 28 Apr 2007 21:06:59 GMT, snipped-for-privacy@ipal.net Gave us:

Actually, things like creepage distances and what not will likely be.
Input leads will need to be fed through teflon tubes or the like.
You could step down your source, then feed your final transformer in a two stage scenario as well. That will reduce problems a bit.
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On Sat, 28 Apr 2007 18:34:49 -0700 SuperM
| On 28 Apr 2007 21:06:59 GMT, snipped-for-privacy@ipal.net Gave us: | |> I'm presuming the necessary primary insulation is going to be |>the major factor limiting how small this can get. | | | Actually, things like creepage distances and what not will likely be. | | Input leads will need to be fed through teflon tubes or the like. | | You could step down your source, then feed your final transformer in a | two stage scenario as well. That will reduce problems a bit.
The combined size would have to be considered in a two stage scenario.
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On 29 Apr 2007 18:15:19 GMT, snipped-for-privacy@ipal.net Gave us:

Of course.
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Look for information on metering PT (potential transformers). They are usually capable of a 100VA or so. As far as I know, they are the smallest commerically available transformers to do what you want. They are solid (no oil) and need no cooling. As for the actual dimensions, I hate to hazard a guess. The bushings are the largest part.
Charles Perry P.E.


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wrote:
| Look for information on metering PT (potential transformers). They are | usually capable of a 100VA or so. As far as I know, they are the smallest | commerically available transformers to do what you want. They are solid (no | oil) and need no cooling. As for the actual dimensions, I hate to hazard a | guess. The bushings are the largest part.
Could the bushings be smaller if the entire transformer case were of some appropriate non-conductive material?
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wrote:

The entire transformer is usually rubber for a 15kV class metering PT.
Charles Perry P.E.
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