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To: hmaly who wrote (164384)	7/9/2005 9:02:50 PM
From: TGPTNDR	Read Replies (3) \| Respond to of 275872

Harry, Re: which makes big devices,(it used to be rows of capacitors, I believe), now they are like magnets, which store electricity, in coils, just for such an event. He said they were used as back up in hospitals though, for what it is worth,however I assume something similar would be used there.> It sounds to me like those THINGS were used to take/provide high instantaneous loads. Like when you turn on a heavy air conditioner or big motor and the lights dim for 1/4 second or so. I'd GUESS that when a MRI machine(as an example) was powered up it would take substantial overcurrent before it got to steady state. Capacitors and BIG magnets are good for storing that kind of power. It's why Capacitor Start motors can generate high initial starting torque. I worked in a datacenter. Nowhere near as important for uninterupted power on the micro level as I would imagine for a fab. We used a room full of lead-acid cells, just like car batteries, but much bigger linked for primary failover.(The power busses and cables were truly impressive. Copper busses ~1/2 inch thick and ~6 inches wide.) Secondary was 5 Turbo Generators but they took 30 seconds or so to get to power. So those batteries had to keep the critical circuits going for those ~30 seconds. When there was an actual commercial power failure we'd lose everything -- on an instantaneous basis -- for most things but the main computers. Lights flicker, local computer screens shrink, etc. (As you do at home when a minor failure causes a drop of a couple of cycles.) But the main computers were fed directly from the batteries via inverters. They'd never see a ripple. After a couple of cycles ( Call it 1/30th of a second )the next most important stuff would stabilize as the batteries picked up that load, lighting and local programmers computers. Then you'd hear the turbines start. Around 30 seconds later the heat, air conditioning, and everything else would be back on the turbines. During the summer months the power company would ask us to go 'off line' when they were having capacity problems. On those occasions you'd hear the turbines start, ramp speed, then take power but there was no flicker at all as they went to backup and cut primary power. (Or maybe we were selling power back to the power company.) Folks who are better versed can chime in. This is all remembered STUFF from a building tour back in 1985 and working in the place 'till Y2K. What is current practice? -tgp

To: hmaly who wrote (164384)	7/10/2005 12:36:18 PM
From: Joe Senesac	Respond to of 275872

I know quite a bit about this due to my work over the past 13 years in biotech manufacturing. The same sorts of designs for the cleanroom backup power are in place for biotech relative to fabs. You generally have 4 major elements: 1) large diesel generator or generators for supply to all key power outlets in building 2) very fast switchgear to rapidly change from incoming utility supply to generator 3) "building UPS unit" which is very large battery unit to cover the initial 50-100 ms period during switchover, and then provide smoothing of the supply during the rest of the period while the generator is getting up to full run. This is a very large unit, think of a pallet sized UPS about 5 feet tall 4) local UPS units to provide conditioned power to any equipment that is still fussy about switchover The switchover time period is the key - for some pieces of equipment, dealing with a 50 ms interruption of power is not a problem, for others it might as well have been completely switched off. Essentially is subject to a complete "reboot", whatever that means for a given equipment, which can be disastrous if in the middle of a production run. Therefore, the building "UPS" unit is a key part of the design. We learned about how important this is after the facility was already operational and had to retrofit a building UPS into the design. The local UPS units can still be important, to help further condition the electrical signal during periods of noise - such as brownouts or these switchover events. Not an electrical engineer, but a biologist/chemist. Was a biotech facilities manager for about a year. Joe