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Achieving cost-effective, scalable UPS solutions at the megawatt level Rapidly growing demand for data capacity means that data centre power


requirements are increasingly reaching megawatt rather than kilowatt levels. In this article, Kenny Green, Technical Support Manager at Uninterruptible Power Supplies Ltd, a Kohler company, looks at how UPS providers can respond to this challenge while maintaining the availability and energy efficiency standards enjoyed by lower power installations.


DATA CENTRES are getting larger, sometimes dramatically so. In Langfang, China, construction is under way at the Range International Information Hub. When completed in 2016, this commercial data centre will become probably the largest in the world; covering 6.3 Million square feet, it will be nearly the same size as the Pentagon. Other data centres of a million square feet or more are already in existence across the US and other parts of the world.


Although these extremes are unusual, they reflect the growing trend for larger-scale processing facilities for enterprises of all types and sizes. We all increasingly rely on our Smart devices and computers for our transactions, searches for information and socialising, while the last two or three years have also seen rapid growth in machine to machine (M2M) communications. According to a market research report published by MarketsandMarkets, the automotive and transportation data communication sector has the highest projected growth, with a CAGR of 33.5% from 2012 to 2017.


As enterprises gear their data centres to accommodate the capacity demand generated by these factors, they find that their power demand is increasingly being reckoned in megawatts rather than tens or hundreds of kilowatts. As these larger facilities come on line, their users have an even greater need for energy efficiency, green operation, availability and flexible scalability than smaller operations do; the consequences of underperformance or failure grow as the data processing load grows.


40 www.dcsuk.info I February 2015


Uninterruptible power supply (UPS) vendors are increasingly able to meet these larger requirements, by scaling their technology as required. One powerful approach is based on transformerless modular UPSs; while kilowatt-level modular systems have been widely established for many years, megawatt implementations have now become possible.


We can see how UPS installations of all sizes can achieve the benefits they need by taking a closer look at the technology now available across all levels of power requirement.


Significantly increased energy efficiency – and significantly reduced size and weight When on line UPSs first became popular in the Seventies, their design used an internal step-up transformer. These have remained popular for many years, especially for larger systems. However the industry has more recently moved towards transformerless technology because, as we shall see, doing so offers many advantages.


Transformerless topology has become viable through advances in power semiconductors and the appearance of the Insulated Gate Bipolar Transistor (IGBT). This has allowed UPS designs in which the DC level supplied to the output inverter is boosted; the AC output from the inverter is correspondingly higher, eliminating the need for the step-up output transformer that previously followed the inverter.


Eliminating the transformer has a significant impact on the UPS’s overall efficiency; as Fig. 1 shows, this increases by around 5% to yield a substantial reduction in energy running costs and heat losses. We can also see that the transformerless efficiency curve remains flat for loads from 25% to 100%, while transformer-based UPS efficiency drops away steadily as loading decreases from 100%.


Further efficiency savings arise due to power factor improvements. The transformer-based systems present a lagging power factor to the incoming supply, which is well below unity at full load, and decreases further with decreasing load. By contrast, transformerless


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