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Old 09-27-2006, 04:56 AM
Zitibake Zitibake is offline
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Default diesel UPS/rotational power supply?

Can anyone comment on the use of a "constant power supply" or "rotational power supply" or "diesel UPS":

http://www.hitzinger.co.uk/dieselups.htm
http://www.hitecelectric.com/en/diesel_ups/

Hitec sells them down to 25kva, but searching around, I've seen datacenters using a half-dozen or more of the 1.8mva or larger units. Do datacenters use these in lieu of battery UPSes? Or use it to back-up just the A-side or B-side power, keeping one side on traditional battery UPSes + gen-set? Or just keep using traditional batteries, but use the "diesel UPS" as an additional layer of UPS?

Any comments on how they're priced, compared to a traditional gen-set plus several UPSes?

It looks like to do maintenance, you'd have to bypass the whole gen-set; if you didn't run the power through another UPS, you might have to run on unfiltered power during the flywheel's yearly maintenance (?).
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Old 10-07-2006, 02:09 PM
Zitibake Zitibake is offline
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Caterpillar sells a gen-set/flywheel combo, which they bill as a "kinetic UPS". It appears that you can take the flywheel off-line for maintenance without bypassing the whole unit. It doesn't appear to be too much different from using a diesel gen-set, with a standard UPS backed-up by a bunch of Pentadyne flywheel cabinets (except the Caterpillar flywheel is claimed at 300kva per cabinet, while Pentadyne's is claimed at 190kva per cabinet). If you use a full UPS+flywheels, you get double-conversion, while the Caterpillar design is line-interactive.

It may be nice (cheaper?) to have the whole gen-set + UPS installed by Cat, rather than designing your own arrangement of transfer switches, etc. On the other hand, there are more electricians to bid-out than Cat resellers.

Google seems to show more datacenters listing the Hitec unit than anything else.
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Old 10-08-2006, 03:49 PM
Zitibake Zitibake is offline
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It looks like Caterpillar is rebranding Active Power's 1200kva line-interactive UPS. It's interesting that PowerWare is selling a double-conversion UPS using the same Active Power flywheel, so if you want the Active Power flywheel with an extra power conversion, there's an option.

The Active Power flywheel system scales larger per cabinet (500kva) than the Pentadyne (190kva), but the cabinets area heavier per kva.
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Old 10-09-2006, 10:06 PM
gallant gallant is offline
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Default Static and Rotary UPS

Just to clarify things a little;
There basically three types of UPS;
• Static UPS. This you basic chemical battery based UPS with no moving parts. Energy is stored as chemical energy in a wide variety of battery types. There are a variety of architectures within this type of UPS. These architectures include:
o On line, double conversion (MGE, Powerware, Liebert etc…)
o Delta conversion (APC)
o Line interactive (Too many to mention, usually less than 5000VA)
o Standby (Too many to mention, usually less than 5000VA)
o Ferro-resonant (Best, Sola)
• Rotary UPS. This type of UPS stores energy as rotational mechanical energy instead of chemical energy. There are two main types of Rotary UPS
o Motor generator. (Hi-Tec, Pillar)
o Flywheel. (Active Power)
• Hybrids. For example; chemical batteries that are backed up or ‘hardened’ by using a flywheel.
Years ago, most UPS equipment was of the rotary, motor-generator type. As the economics of solid state electronics and transistorized components became more appealing than the motor generator sets, static UPS equipment began to become more common. Prices for static UPS components continued to drop and their reliability, efficiency and performance characteristics improved. Eventually, the static UPS became much more prevalent than rotary. However, the rotary UPS never really went away.
For some users, UPS loads were so big that the economics of the static UPS did not make sense. The batteries required to support a 1.8MW load are extremely expensive in terms of initial cost, maintenance costs and replacement costs. The ROI for motor generator type UPS systems gets very appealing as systems gets larger. By the time you get to a UPS system load of 5MW, rotary UPS equipment is the only way to go. Most static UPS manufacturers don’t build systems larger than 5MW and don’t build UPS modules any larger than 1MW
These days (with the trend towards cloud computing and other market drivers), massive data centers with motor generator UPS systems are becoming more common on mission critical drawing boards.
The other type of rotary, the flywheel, is simply an alternative to a battery. In many cases, your static UPS can be retrofitted with a flywheel energy storage system. That’s why you see Active Power flywheels used in tandem with all types of static UPS manufacturers like Caterpillar and Powerware. The problem with flywheels is that, compared to batteries, they don’t store that much energy. But, if you have generator you typically only need 10 seconds or less anyway. These flywheels also are a very good way to extend the life of your battery system. By applying both a flywheel and a battery plant, you can prevent small outages and power fluctuations from causing battery discharges. Fewer discharges equals longer battery life.
As far as maintenance on the motor generator UPS goes, you design in redundancy. If you have the money to buy these big systems, buy a redundant (N+1) unit. Or better yet, a redundant system (2N). Sometimes people forget that the reason for redundancy is not only to save you in the event of an equipment failure, but also to allow you to perform preventive maintenance without compromising your availability.
As far as maintenance on the flywheel UPS goes, in most cases you can isolate the flywheel from the rest of the UPS for maintenance in precisely the same way you can open a battery breaker on a static system. Simply open the breaker. As always, redundancy works.
I hope this information helps,
ericgallant
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