Is it time to consider medium voltage UPS systems in large scale data centers?
ABB
A short ABB article arguing that very large data centers close to strong transmission networks may be better served by industrial single-conversion UPS than by double conversion.
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Overview
The article's argument rests on grid character: very large data centers connected close to strong transmission networks mostly see short sags and micro-interruptions. On such a grid, instead of isolating the load with continuous double conversion, a single-conversion (offline/line-interactive style) industrial UPS at low or medium voltage can give adequate protection.
Three advantages of industrial UPS are listed. First, higher overload ratings, which ease protection selectivity. Second, efficiency above 99%. Third, compatibility with lead-acid, lithium-ion and supercapacitor storage, with lead-acid giving the lowest capex. Single-conversion industrial UPS units are available up to 6 MVA at 208-480 V and in MV. The timing constraint is firm: the UPS must bridge until generators reach speed, and the generator must typically take load within about 10 s, which fire and life-safety mandates in many countries also require. UPS ride-through must therefore exceed generator start plus transfer time with margin.
The 2014 article is brief and does not quantify the cost of reduced conditioning (the chance that voltage and frequency disturbances reach the load) against the efficiency gain. The conclusion holds only for sites with a strong grid and loads tolerant of disturbance; on a weak grid double conversion is still needed.
Key points
- Generator must typically take load within ~10 s (fire/life-safety mandates in many countries)
- Industrial single-conversion UPS ratings up to 6 MVA, 208-480 V and MV
- Single-conversion efficiency >99%
- Storage options: lead-acid (lowest capex), Li-ion, supercapacitors
- Higher overload rating eases protection selectivity
Using it in design
- Add "single-conversion / industrial (VI)" to the UPS topology picker for hyperscale sites with a strong grid, showing efficiency (>99%) beside reduced conditioning.
- Default generator start-to-load time to 10 s.
- Set minimum UPS ride-through above generator start plus transfer time, with margin.
- In storage selection compare lead-acid for capex against Li-ion and supercapacitors.
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Who should read it
Electrical designers choosing UPS topology for hyperscale sites on strong grids.
Related standards
- IEC 62040-3
- NFPA 110 (Type 10)
- IEC 60364
Publication details
- Authors
- ABB
- Publisher
- ABB
- Year
- 2014
- Document number
- 9AKK106103A5938
- Document language
- English
- Source type
- Manufacturer
- Access
- Free to read
- Licence
- Copyright retained; citation only — the publisher’s terms apply to the original document
Citation
ABB (2014). Is it time to consider medium voltage UPS systems in large scale data centers?. ABB. 9AKK106103A5938. https://library.e.abb.com/public/5f8a9d16f3ad6aa785257ce6004806e3/medium%20voltage%20ups%20systems%20in%20large%20scale%20data%20centers_rev3.pdf
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