Let’s discuss the copper

Data center owners are opting for even larger servers, adding even more copper.
By Joe Guentert, Owner, Power Distrubtion Systems June 20, 2012

Last week, we discussed the differences in construction costs and copper requirements between the competing approaches of locating medium-voltage transformations outdoors, and connecting the secondary loads via large underground duct banks, versus moving the transformations indoors, in close proximity to the loads.

Image of multiple duct banks with 12 4'' conduits. Courtesy: Joe Guentert 

The differences between the two approaches are becoming more pronounced recently, as more and more data center owners are opting for 230 V servers, and are distributing large critical power at 415 Y/240 V. That necessitates a full-size (and sometimes, an OVERSIZED) neutral, which adds at least another third to the tonnage and the cost of the copper in secondary feeders. I have seen some very large data center designs on the boards recently that will have more than 4 million lbs of copper in underground duct banks or cable tray, just to get 600, 480, or 415 V utility power and generator power into the low-voltage main distribution switchgear lineups, before the power is even distributed to any loads.

Some large data center owners who are moving to modular containers in their centers also have moved to switchgear containers and skid-mounted unit substations outdoors, close-coupling the transformations to the secondary switchgear. That removes all the copper between the transformer and the switchgear, but then adds back even MORE copper on the distribution feeders from the switchgear into the loads.

           

I’ve seen “modular” projects recently where the secondary switchgear was located outdoors, close-coupled to substation transformers, eliminating the need for a 4000 A or so secondary duct banks into the building. But those 4000 A trunk feeders were then replaced by branch distribution feeders in duct banks or cable tray having a total aggregate ampacity of 10,000 A or more, to distribute to the loads.

Image of multiple duct banks with 16 4'' conduits. Courtesy: Joe Guentert

I think that this pronounced trend of load growth cries out more loudly than ever before in history for a real and true “loadcenter” approach, with the transformations located right down in the center of the loads, where little 4000 A braided flex links like these, connecting a transformer to its secondary switchgear, can replace all those duct banks and hundred of tons of copper.

Image of 4000 A braided flex links, connecting a transformer to its secondary switchgear. Courtesy: Joe Guentert

If you can accept that this makes sense, what are the options? Until fairly recently, almost all of the loadcenter substation transformers that went inside data centers since 1995 were either VPI dry-type or epoxy cast coil construction.