NSA's electrical power problems

[Mike O'Dell]

Put all those highly-reactive loads as lumped constants
attached to very very long bussbars and you have a 
pathological combination.  The Pentagon does its 
distribution on buss bars ("buss-way") but the loads
there are nothing like a big data center. The more expensive
but correct way to solve the problem is lots of home-runs
back to PDUs in a star arrangement (and the PDUs home-run
back as well). that way the buss bars and the reactive
power supplies don't form a transmission line of 
resonant circuits at switching power supply frequencies 
and make lots of volts that are quite unexpected by
power engineers not member of the Big Data Center Guild.

Note that power supplies must be power-factor-corrected
to be CE-marked and hence are much less likely to provoke
the gods.

Doing 400VDC distribution is another way to attack the problem, 
and it works well with big UPSes, but stars are still better than
long long bussbars. and with 400VDC distribution, there
are often electrical code and/or union issues that arise,
not to mention the need for special powersupplies in all
the kit. and if you are willing to do that, just get
PF-corrected supplies. 

a couple of us know the chap who built what was for 
quite some time the largest multi-tenant data center
in the world - 350 East Cermak in Chicago. I asked him
about the story and he related the prolonged argument
he had with the electrical contractor who kept insisting
that buss-bars would not be a problem and would save a lot
of money (not to mention had much higher margin than the
man-hour-intensive home-runs). he knew better from previous 
(painful) experience and finally said "My project, my money, 
so it's my way, period." 

he suggested that if they in fact did buss bars (almost
certainly what the lowest bidder would have used),
they are in a *world* of hurt and it's gonna be
a huge amount of work and even a bigger amount of money
to fix it right.

   You Tax Dollars At Work!
       -mo

There is a *huge* difference between "inexpensive" and "cheap".