Big Data, as its name suggests, concerns large volumes of complex data that if correctly processed can be a powerful tool for many enterprises. 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, a Kohler company, looks at how modern modular UPS systems can help operators meet the challenges of ‘Big Data’
The term ‘Big Data’ refers to collections of data sets that become difficult to process using traditional database management tools, due to both size and complexity. These data sets are growing because they are being gathered by increasingly ubiquitous information-sensing devices of all types, in addition to the ever-increasing traffic generated by 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, determine quality of research or characterise other ‘big picture’ scenarios. However, this type of data can require 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 its possible rapid growth. These considerations extend to UPS systems, which are now essential to any data centre’s infrastructure. Operators are seeking UPS systems large and flexible enough to meet these challenges, while maintaining or improving upon the availability and efficiency performance 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 modern, modular UPS technology. We can show how this is possible by looking at the underlying UPS modules and how they are deployed within a system to create a Big Data solution.
During the mid-seventies, on-line double-conversion UPSs became widely adopted, especially in the highest power applications for the time. These systems used transformers to step up the UPS inverter output to match the incoming mains supply voltage level. More recently, advances in semiconductor technology, the development of the Insulated Gate Bipolar Transistor (IGBT) device and improved methods of Pulse Width Modulation (PWM) waveform generation within these systems has driven a move to transformerless UPS systems.
Within transformerless systems, the earlier phase-controlled rectifier has been replaced by a significantly more compact fixed rectifier followed by a DC-DC booster. This elevates the DC level fed to the UPS inverter, allowing it to reach the required output AC voltage level without needing a step-up transformer. As we shall see, these changes, together with the modular topology that they enable, allow UPS systems 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%.
A transformerless system’s power factor is also much closer to unity than that of a transformer-based system. This reduces the input supply current magnitude and therefore the sizing of associated cables and switchgear.
Total input current harmonic distortion (THDi) is also significantly reduced. This virtually eliminates harmonic pollution of the mains supply, saves unnecessary oversizing of gen-sets, cabling and circuit breakers, avoids extra heating of input transformers and extends 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-mounted modules rather than single large unit. This topology offers previously unavailable levels of flexibility, scalability and availability, even on very high power systems.
Uninterruptible Power Supplies’ (UPS Ltd) latest high power UPS product, the PowerWAVE 9500DPA, provides the best available demonstration of how users can now benefit from modular UPS technology, even at megawatt levels. The system is based on rack-mounting UPS modules rated at 100 kW each. It is scalable because its frame can accommodate up to five modules to share the total UPS load. A PowerWAVE 9500DPA 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 with up to five modules, delivering up to 500 kW in total. 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.
UPS systems based on modular topology have an extremely low mean time to repair (MTTR); this allows very high levels of UPS availability. MTTR is low because if a module fails, it can be removed from the UPS frame quickly, by simply sliding it out; a replacement can be fitted similarly. The entire operation is performed without interruption of mains power to the load and MTTR has been cut to an absolute minimum.
For an example of redundancy in a UPS system, consider a 400 kW load being shared equally by a set of five 100 kW modules. If one module should fail, the remaining modules can continue supporting the load without interruption as they still have the required 400 kW capacity. During normal operation one module is effectively redundant; a mode known as N+1 redundancy.
Suitability for Big Data scenarios
Modular UPS systems can achieve up ‘six nines’ availability – that is, up to 99.9999%. Overall, modular technology provides data centre operators with the right UPS tools to meet many Big Data scenarios. By using vertical and parallel scaling, megawatt UPS capacity can be provided, together with rapid scaling to meet fast-changing data capacity demands. These power levels are available with efficiency levels better than 96%, or even 99% if eco-mode operation is used, while availability is also at the level demanded by Big Data and most other loads today.