Recommended reading: UPS terminology 101

To understand how uninterruptible power supplies work, you need to know a few things about important concepts and topologies. In a recently launched article series on DatacenterDynamics, Alan Luscombe, director at Uninterruptible Supplies Ltd, shares short explanations of the most relevant UPS teminology.

In the first article he explains why nearly all data centers use online UPS topologies. In the second part of his series Alan explores why static, double-conversion online UPSs today invariably use transformerless technology.

“Its key advantage is efficiency, which increases by around five percent, with improvement across the entire load spectrum. This substantially reduces both electricity and cooling expenditure. Transformerless designs also yield a higher input power factor, which remains near unity with minimal load dependence. Input current magnitudes, and therefore cabling and switchgear sizing, are reduced. This sometimes cuts electricity costs.

In addition, the total input current harmonic distortion (THDi) in three-phase UPSs reduces from around 30 percent to below three percent through transformerless technology. Limiting harmonic emissions contributes considerably to meeting the Energy Networks Association G5/4-1 recommendations concerning satisfactory operation of the electricity supply system with connected equipment, through EMC compatibility.

Transformerless topology also has physical benefits, bringing profound changes to the UPS industry. Eliminating the transformer and the 12-pulse rectifier previously required considerably reduces both size and weight. The total system footprint is more than halved, while weight is cut by about three-quarters. Such reductions mean that UPSs become rack-mounting modules rather than monolithic floor-standing units.”


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