There are five principle UPS system design configurations that distribute power from the utility source of a building to the critical loads of a data center. The selection of the appropriate configuration or combination thereof for a particular application is determined by the availability needs, risk tolerance, types of loads in the data center, budgets, and existing infrastructure. This paper will focus on these five configurations; the advantages and disadvantages of each are discussed. The impact on availability is addressed for each configuration and guidelines are provided for choosing the appropriate design.
Over time, many design engineers have tried to create the perfect UPS solution for supporting critical loads, and these designs often have names that do not necessarily indicate where they fall in the spectrum of availability. “Parallel redundant”, “isolated redundant”, “distributed redundant”, “hot tie”, “hot synch”, “multiple parallel bus”, “system plus system”, “catcher systems, and “isolated parallel” are names that have been given to different UPS configurations by the engineers who designed them or by the manufacturers who created them. The problems with these terms are that they can mean different things to different people, and can be interpreted in different ways. Although UPS configurations found in the market today are many and varied, there are five that are most commonly applied. These five include: (1) capacity, (2) isolated redundant, (3) parallel redundant, (4) distributed redundant and (5) system plus system. We now describe each of these.Capacity or “N”
A Capacity or “N” system, is comprised of a single UPS module, or a paralleled set of modules whose capacity is matched to the critical load projection. This type of system is by far the most common of the configurations in the UPS industry. The small UPS under an office desk is an N configuration. Likewise, are large computer room with a design capacity of 400 kW is an N configuration whether it has a single 400 kW UPS, or two 200 kW UPS paralleled onto a common bus. An N configuration can be looked at as the minimum requirement to provide protection for the critical load. Most “N” system configurations, especially under 100 kW, are placed in buildings with no particular concern for the configuration of the overall electrical systems in the building. In general, buildings’ electrical systems are designed with an “N” configuration, so an “N” UPS configuration requires nothing more than that to feed it.