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FACILITIES power+cooling


UPSs present a full-load input power factor which is much closer to unity and remains load-independent.


Total Harmonic Distortion (THDi) is reduced from around 30% to around 3%, virtually eliminating harmonic pollution of the incoming mains supply. Overall, the magnitude of the input currents is reduced, which in turn minimises the sizes of the cabling and switchgear, and in some circumstances reduces electricity running costs.


Transformerless technology’s contribution to energy saving is matched by the substantial saving in size and weight it provides. This is because transformerless systems not only eliminate the transformer, but also operate with a much smaller rectifier.


example, ‘W’ equates approximately to ‘VA’ as the UPS power factor is close to unity.


Fig. 1: UPS ac-ac efficiency curves for transformerless and transformer-based topologies


For example a 120 kVA transformer-based UPS has a footprint of 1.32 m2 and weighs 1200 kg, while its 120 kVA transformerless alternative has a footprint of 0.64 m2 and weighs just 310 kg.These physical factors have had a profound effect on UPS development, as they are sufficient to allow UPS units of up to 100 kVA to be implemented as rack-mounting modules instead of cumbersome standalone systems. This brings major benefits in terms of parallel redundancy, right sizing and extensive scalability. These are in addition to the efficiency, energy saving and reduced cooling costs provided by the underlying transformerless topology.


Modular scalability benefits – a practical example Uninterruptible Power Supplies Ltd, a Kohler company, has recently introduced their latest modular three-phase UPS system – The PowerWAVE 9500DPA. This exhibits all the benefits of modular topology on a system that scales from 100 kW to 3 MW, taking users up into megawatt power levels when their circumstances demand it. In this


PowerWAVE 9500DPA starts with a single frame which can accept up to five UPS modules, each rated at 100 kW. Therefore the UPS could be populated with one module to support a 100 kW load, then more modules can be added, incrementing the UPS capacity in 100 kW steps to keep pace with its growing critical load. This process is known as ‘Vertical Scalability’. If the load then grows beyond 500 kW, up to six frames can be paralleled to achieve a total capacity of 3 MW. This second dimension of expansion is known as ‘Horizontal Scalability’.


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. The PowerWAVE 9500DPA delivers an availability of 99.9999% (Six Nines) by minimise the mean time to repair (MTTR).


For example that the UPS has to support a 400 kW load. When fully populated, a single PowerWAVE 9500DPA frame has 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.


If a module does fail, the PowerWAVE 9500DPA’s ‘Hot Swap’ capability allows the faulty module to be removed and replaced, without need to power down the UPS. MTTR is minimised, availability is maximised, and power to the load continues without interruption.


PowerWAVE 9500DPA – megawatt-level power with high availability and high efficiency


The PowerWAVE 9500DPA UPS is ideally suited to megawatt-level critical loads, because it offers the availability levels essential to such installations, while also addressing their need to minimise energy and cooling costs. Its true online efficiency is 96%, which can be increased to 99% in Eco-mode operation. Capital expenditure and space requirements are also minimised, as its power capacity can be closely matched to the critical load size, even if this changes.


For more information about Uninterruptible Power Supplies Ltd and the PowerWave services they offer visit www.upspower.co.uk


February 2015 I www.dcsuk.info 41


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