[Beowulf] Re: UPS & power supply instability

[David Mathog]

> 
> > I liked Jim's idea of trying a 
> > balanced, large resistive load on the lines.  A heater, an electric
> > range.
> 
> I want to say (but am not sure at the moment) that the instabilities
show up 
> at around 140kW.  I don't have 140kW of resistors available easily, let 
> alone a full-power load of 350kW. 

Sure, but if things are really, really, badly screwed up one
might see a largish neutral current, percentage wise, no
matter what size the resistive load.  Try three matched
space heaters (one per phase) and see if the neutral current
is zero.  If it isn't then you (or your electrician) can
diagnose at least part of this problem without having to plug
in a full load. 

For the experts out there: could a huge iron pipe, or a lot
of iron rebar, produce this much of an inductive load if these were
located just below the floor, say 6 inches from the power
lines running to the racks?  The lab in question is on
the bottom floor of the building so there could conceivably 
be something like that underneath it.  I'm thinking not, but
then I've never worked with the kinds of currents that are present
here.

Regards,

David Mathog
mathog at caltech.edu
Manager, Sequence Analysis Facility, Biology Division, Caltech