Big Data, as its name suggests, concerns large volumes of complex data that if correctly processed can be a powerful tool for many enterprise; however providing the processing capacity required can call for tens, hundreds or even thousands of servers. This impacts data centre operators who must provide UPS protection of sufficient capacity and flexibility for these new challenges.
In this article, Kenny Green, Technical Support Manager at Uninterruptible Power Supplies Ltd, a Kohler company, looks at how operators can benefit from today’s modular UPS technology in implementing systems that can meet these challenges.
Big Data is a concept and a term which has been widely accepted since around 2012. It refers to collections of data sets that become difficult to process using traditional database management tools, not only because of their size but also through their complexity. These data sets are growing in size because they are being gathered by increasingly ubiquitous information-sensing devices, in addition to the ever-increasing traffic arising from human interaction with smartphones, computers and other user interface devices.
The data sets can become powerful tools and create new opportunities for enterprises seeking to spot business trends or characterize other ‘big picture’ scenarios. However this type of data can require massively parallel software running on tens, hundreds or even thousands of servers.
Data centre operators’ strategies for these new realities must cater not only for the data’s size, but also for the fact that this size is a constantly moving target, and can be volatile. These considerations extend to UPS installations, as these are now essential to any data centre’s infrastructure. Operators will be seeking UPS systems that are large and flexible enough to meet these challenges, while maintaining or improving upon the availability and green energy-efficient performance now considered essential for modern critical data centre loads.
Modular UPS technology
Fortunately, today’s data centres can meet four critical UPS criteria – capacity, scalability, availability and energy efficiency – together with minimal total cost of ownership, through using modern, modular UPS technology. We can show how this is possible by taking a closer look at the underlying UPS modules and how they can be deployed into a system suitable for Big Data loads.
When they originally appeared in the mid-seventies, UPS systems needed transformers to step up their output AC voltage. However advances in power semiconductor technology since then have created a move to transformerless UPS systems. The power electronics within these allow them to reach the required output AC voltage level without needing a step-up transformer as previously. As we shall see, these changes, together with the modular topology that they enable, allow UPSs to meet the challenges imposed by Big Data processing centres.
Efficiency and running cost savings
The most immediate benefits of transformerless operation are improved electrical efficiency, with reduced electrical losses and cooling costs and, just as importantly in today’s political and social climate, a greener mode of operation. As Fig. 1 shows, eliminating the transformer improves the UPS’s overall efficiency by around 5%, while providing an efficiency curve that remains flat from full loading right down to 25% of load. By contrast, transformer-based system efficiency reduces significantly as the load drops away from 100%.
Fig.1: Overall UPS efficiency curve
UPSs using transformerless technology impose a power factor much closer to unity, which reduces input current and sometimes electricity running costs. Total input current harmonic distortion (THDi) is also reduced, virtually eliminating harmonic pollution of the mains supply, saving unnecessary oversizing of gen-sets, cabling and circuit breakers, avoiding extra heating of input transformers and extending the overall lifetime of all input components.
Scalability and availability
While the energy savings allowed by transformerless technology are extremely important, the reductions in size and weight also have far-reaching effects. These reductions result from eliminating both the transformer and the phase controlled rectifier. A transformer-based 120 kVA UPS, for example, weighs 1200 kg and has a footprint of 1.32 m2. By contrast, a transformerless 120 kVA UPS weighs just 310 kg, with a footprint of 0.64 m2.
The factors of reduced size and weight have had a profound effect on the development of the UPS and the entire power protection culture. They allow a UPS system to be implemented as a set of relatively small, independent, maneuverable rack-mounting modules rather than single large unit. This topology offers previously unavailable levels of flexibility, scalability and availability, even on very high power systems.
Today, these rack-mounting UPS modules can be rated at up to 100 kW each. The installation is scalable because a UPS frame can accommodate up to five modules to share the total UPS load. A new UPS system, for example, could be installed to supply a 100 kW load, achieved with a single 100 kW module slotted into the UPS frame. The frame can then be populated incrementally until it reaches its full complement of five modules, delivering up to 500 kW in total. Incrementally populating the UPS frame like this is known as vertical scaling. If further capacity then becomes necessary, additional UPS racks can be installed, allowing total loads of megawatts rather than hundreds of kilowatts to be supported. Paralleling frames to add capacity is known as horizontal scaling.
This ability to start at 100 KW or less, and scale on demand right up to MW levels, allows data centre UPSs to handle Big Data loads, even when their size grows rapidly.
Achieving the highest possible power availability is essential to any UPS installation – ultimately, it’s the only reason for investing in a UPS at all. Today, UPSs of all sizes can deliver an availability of 99.9999% (Six Nines) by minimising the mean time to repair (MTTR). For example, suppose that the UPS has to support a 400 kW load. A UPS frame could achieve this with five 100 kW modules, which share the 400 kW load during normal operation. If any single module fails, the remaining four can continue to fully support the load. Known as N+1 redundancy, this arrangement can improve the system availability. Modern, modular UPS systems can also offer ‘hot swap’ capability. This means that if a module does fail, it can be removed and replaced without the need to power down the UPS. MTTR is minimised, availability is maximised, and power to the load continues without interruption.