DCA REVIEW Industry Trends & Standards
runtime of about 10 minutes will be sufficient to ensure that the ICT equipment has a safe, well-ordered shutdown. If the application must continue running throughout a power outage, the UPS must be provided with extra batteries or, preferably deployed with a back- up generator.
To summarise, we have seen that the UPS’s job is to be always available, providing a level of protection from mains supply failures and events compatible with the nature of the critical load. However, we have also mentioned that in today’s conditions it must achieve this with the best possible energy efficiency and easily-implemented scalability. Modular UPS topology.
The solution lies in both the technology and the topology available in the latest developments in UPSs. Whereas, earlier- design UPSs used a transformer to step up their inverter’s output to the required AC voltage level, advances in power semiconductor technology, particularly the Insulated Gate Bipolar Transistor (IGBT) have allowed the transformer to be eliminated. This has had a number of profound effects on modern UPS design.
Firstly, transformerless UPSs are about 5% more efficient than transformer-based products. Fig.2 shows this, while revealing that efficiency is improved over the entire load spectrum from 100% down to 25%. As a result, substantial reductions in electricity running costs and heating losses are achieved. Additionally, the power factor is improved, while total input current harmonic distortion (THDi) is reduced, bringing further cost savings and improved reliability.
While transformerless technology is extremely important for its energy savings, its 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 significance of this is that it allows UPSs, even in high power installations, to be configured as sets of independent rack- mounted modules. For example, with the PowerWAVE 9500DPA, up five modules, each of 100 kW, can be accommodated within a single UPS frame. A UPS can be scaled to a 100 kW load with a single module, then
Fig.1: Typical UPS block diagram
incremented in 100 kW steps to 500 kW, matching the load as it grows. This flexibility in populating the frame is known as vertical scalability. For loads beyond 500 kW, up to five additional frames can be added, providing horizontal scalability up to 3 MW.
Alternatively, a <400 kW load can be supported by five 100 kW modules. This means that if one module fails, the other four can continue to fully support the load, as they still have 400 kW capacity between them. As one module is redundant, this is known as N+1 redundancy. Modules can be ‘hot-swapped’; a process where a faulty module can be removed, simply by sliding it out of the UPS frame, and replaced with another without interrupting power to the critical load. This also has a positive effect on Mean Time to Repair (MTTR).
Minimised MTTR contributes to increased
availability, with modular UPS systems offering availabilities to 99.9999%. These UPSs are well-equipped to fulfil the critical power protection role expected of them by today’s data centres – and they can do so with a true online efficiency exceeding 96%. The last 30 years of UPS development has without question had a significant effect on IT power security and today, R&D is still responsible for driving sales growth – meaning you can count on further step changes in efficiency in the coming years. So, as the way data centres are used and managed develops over the next decade, UPS manufacturers will undoubtedly continue to invest and innovate, using the latest technological advances to ensure your load is as protected as it ever can be.
For more information about Uninterruptible Power Supplies Ltd and the UPS Systems they offer please visit
www.upspower.co.uk
Fig.2: Transformer-based and transformerless UPS efficiency curves May 2014 I
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