I have a 6KVA sandpoxy-filled transformer I'm digging out right now (thread on the excavation) and much to my surprise when I finally unearthed the transformer, it has 2 cores.
It's a Square D model # 6T2F, 480V Delta input, 208/120V Wye output according to the generic info I can find online. The data plate was worn off mine so I didn't notice the odd connection diagram; here's what it would look like though (not my picture):
It says "Type ST" on the label, there's 2 cores, and the connection diagram seems to confirm a Scott T transformer, for which the only purpose I was aware of, is to generate archaic 2-phase power from a 3-phase supply. But everything I can find online says it's a general purpose 3-phase transformer (to quote the page linked above: "General Purpose - Intended for power, heating and lighting applications").
I pulled this out of a dumpster years ago at a place I worked. I was an Electrical Maintenance Tech there, and I was familiar with nearly all of the equipment on site. There were absolutely no 2-phase machines on site that I am aware of. I am 99% sure that this transformer was never used to generate 2-phase. If memory serves, I believe I was told that it was a spare for an old industrial trash compacter that was scrapped.
I went searching for answers as to why anyone would use a Scott T transformer for uses other than generating 2-phase, and found this:
It's a Square D model # 6T2F, 480V Delta input, 208/120V Wye output according to the generic info I can find online. The data plate was worn off mine so I didn't notice the odd connection diagram; here's what it would look like though (not my picture):
It says "Type ST" on the label, there's 2 cores, and the connection diagram seems to confirm a Scott T transformer, for which the only purpose I was aware of, is to generate archaic 2-phase power from a 3-phase supply. But everything I can find online says it's a general purpose 3-phase transformer (to quote the page linked above: "General Purpose - Intended for power, heating and lighting applications").
I pulled this out of a dumpster years ago at a place I worked. I was an Electrical Maintenance Tech there, and I was familiar with nearly all of the equipment on site. There were absolutely no 2-phase machines on site that I am aware of. I am 99% sure that this transformer was never used to generate 2-phase. If memory serves, I believe I was told that it was a spare for an old industrial trash compacter that was scrapped.
I went searching for answers as to why anyone would use a Scott T transformer for uses other than generating 2-phase, and found this:
It seems like this Scott-T transformer should be an odd duck, hard to find, expensive, and used only in a very small, specific niche of applications. But when I search for transformers with a 208Y/120 secondary, half of them are Scott-T types. Why is that? Why are people buying these transformers? Is there an advantage to them that my reference failed to note?The Advantages of the Scott T configuration:
1. If desired, a three phase, two phase, or single phase load may be supplied simultaneously
2. The neutral points can be available for grounding or loading purposes
The Disadvantages when used for 3 Phase Loading:
1. This type of asymmetrical connection (3 phases, 2 coils), reconstructs three phases from 2 windings. This can cause unequal voltage drops in the windings, resulting in potentially unbalanced voltages to be applied to the load.
2. The transformation ratio of the coils and the voltage obtained may be slightly unbalanced due to manufacturing variances of the interconnected coils.
3. This design’s neutral has to be solidly grounded. If it is not grounded solidly, the secondary voltages could become unstable.
4. Since this design will have a low impedance, special care will have to be taken on the primary protection fault current capacity. This could be an issue if the system was designed for a Delta-Wye connection.
5. The inherent single phase construction and characteristics of this connection produces a comparatively bulky and heavier transformer when compared with a normal three phase transformer of the same rating.
7. In a comparative analysis of the published weights of the one commercially available Scott T transformer (only one manufacturer still constructs a dry-type Scott T) and a number of Delta-Wye transformer manufacturers you will find that Scott T’s are, in most instances, lighter than the similar kVA copper DeltaWye units. This goes against the mathematical principals and the sizing requirements stated by “Auten Stigant & Franklin”. It suggests that the Scott T transformers do not meet and are not equivalent to their Delta-Wye equivalent kVAs.
[...]
The Scott T would not be recommended as a connection for 3 phase to 3 phase applications for the following reasons:
• The loads of modern buildings and office buildings are inherently unbalanced and contain equipment that can be sensitive to potential voltage fluctuations that may be caused by the Scott T design.
• A properly sized Scott T transformer will have to be a minimum of 7.75% larger than the equivalent Delta-Wye transformer. Properly sized, it would be a bulkier and heavier option and should not be considered a less expensive solution. Applications requiring 3 phase to 3 phase configuration are best served by a Delta–Wye configuration. This configuration is the smallest and best suited for the unbalanced loads and sensitive equipment of today’s applications that could be affected by voltage fluctuations.