MAE-East still no generator

Sun Sep 8 17:44:44 UTC 1996

> That's why the PAIX is wired thusly:
> 
> [ picture ]
> 
> The batteries are sort of the capacitor in a huge DC power supply.  The
> triple AC UPS is so that the electricians can do maintainance on one of
> the UPSes while still leaving two others online.
> 
> Stephen was talking about dual rectifiers and a DC transfer switch but
> I havn't been in that room for a while so I don't know if that happened.

Last I counted there were five rectifiers. The single-line drawing is
back at my office, though, and I don't recall how they're wired.

> It costs a lot of money -- almost as much as connectorizing the cross
> connects -- but the goal is 100% uptime on both the AC and DC.

Yup. The air conditioning is wired into the city and generator power
so that it will run during a power failure, but not drain the UPS'
batteries. 

The UPS (and DC, of course) batteries charge off the generator - since
it takes longer to charge than it took to drain, sometimes you have to
run the generator longer after city power comes back, to make sure
that the batteries have charged enough should the power fail again
(and perhaps again, and again after that) right after you've switched
back to city power.  It's a worst-case scenario, but if your city
power toggles a couple times in a day, you could lose your entire
battery charge in increments, and not have enough to carry you until
your generator kicks in.

Just out of curiosity, does anyone have any personal experience with
losing utility-provided power more than, say, three times in a day?

Stephen
- -----
Stephen Stuart				stuart at pa.dec.com
Network Systems Laboratory
Digital Equipment Corporation