I work in a company that specializes in 3-phase power converters. Our assembly line electrical test stations need to be able to test our 480V and 208V units, both at 100 A. However, the current reduction at the end of the circuit is only about 5 A. In order to try to save money and electricity, we reroute the remaining 95A back into the test circuit. This means that our power usage for one of these test stations should average maybe just above 5 A multiplied by the test voltage.
Okay. So, the main voltage we run throughout our facility for tests is 480V. We really do not want to run an additional line in order to test our 208V units, or have to run even more lines to test 380V or 400V units as they are developed. Recycling the 480V power is very easy because it can junction directly into the main line. But, we need a transformer to test our 208V units, and as a result we must develop a custom solution to recycle this power while still achieving isolation of the unit under test. That is something I forgot to mention - we need a transformer at each test station in order to ensure all units being tested are isolated from the rest of the building.
Anyway, we have developed a plan to recycle the 208V power in a very unconventional way. We desire to have a custom transformer produced with 480V primary and 480V secondary, as well as 208V taps on both the primary and secondary windings. What we plan on doing for our 208V tests is having 480V power initially enter with relatively high current into the transformer. It would then be transformed into 208V, 100A, and pass through our test unit and test equipment. Once it has passed through all of these, it returns to the input side of the transformer enters the primary winding via the 208V tap. Once the current is steady at 95A entering the primary winding (recall 5A current loss in system), then only a few Amps will be required to sustain the system, entering in the 480V input.
So basically, at t=0:
Then, at t=inf:
Now, the only way this could work is by using Wye connection types on both the primary and the secondary. This would permit two inputs for the transformer, because current and voltage vectors align. This would not be possible for a delta-wye or delta-delta transformer.
So, specs look something like this:
Primary: 480V Wye
Secondary: 480V Wye
Taps: 208V Wye on both primary and secondary
Temp Rise: 150
The main issue that we have is that no one is willing to make it for us. We have tried many custom transformer companies, and received answers ranging from, "it's not safe," to, "you don't have enough volume."
Is this in fact an unsafe design? If it is unsafe, why? If it's not unsafe, why won't anyone produce it?
Thanks for the help in advance!!!