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Q: Can you point us to any documentation on what sorts of requirements we should be asking for in terms of selecting the exact transformer to use? This application will be single-sourced HPC systems, so we'll expect fairly high loading on the transformer most of the time. We need to understand the characteristics/attributes that we want and find them in a USA supplier or justify why we need them and that no USA supplier offers them. Thanks for any pointers you may have.
A: The DOE 2016 requirement for low-voltage distribution transformer efficiency is specified at 35% load, which is probably a good assumption for a commercial building, but a bad one for a data center striving to make the best use of limited power distribution resources. That standard requires no less than 98.83% efficiency (again, at 35% load). Overall transformer losses are the total of a fixed no-load loss and a load loss that scales with the square of the load, thus the DOE standard numbers are dominated by the no-load loss and the high loads that you are striving for will be dominated by the load loss and there are trade-offs in transformer design between the two.
I'd suggest getting the efficiency curve from Powersmiths for their ESAVER-50H (optimized for high loading) and use that to specify the efficiency requirement at e.g. 75% load, which is a standard rating point. Other parameters, especially impedance, need to be managed to optimize inrush current, fault level, and arc-flash to make sure it will integrate with the existing installation. We learned this the hard way at FLEXLAB. Hope this helps!