Transformer design UPS systems, old and new

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Data Center management
Load balancing
Security
UPS system
a)What are the advantages or disadvantages, if any, of traditional transformer design UPS systems, over the "newer" transformer-less systems. b)Related to the above, would a transfomer UPS in redundant parallel configuration, offer greater protection to the load, over the modular, transformer-less design?

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The newer “transformerless” design UPSes tend to be physically smaller and lighter than transformer-based units.
Many of them also tend to be more efficient when operated under partial load (a UPS in a 2n configuration might only run at around 40% of its rated capacity, for example). That said, there are many good UPS systems available, both with and without transformers, so that should not be (IMHO) the determining factor in selection.

In regard to your second question, eliminate the word “transformer” from the question — there are good modular units both with transformers and without. Properly designed, both conventional redundant parallel configuration and modular n+1 configurations give adequate protection. Modular n+1 configurations tend to cost less than redundant parallel configurations.

Remember that the batteries are the part of the UPS system most likely to cause a load-shed failure. Modern UPSes are extremely reliable, but no so their batteries! Whatever the configuration, be sure you have redundant battery strings — redundant parallel configurations have then by definition, as do some brands of modular designs — or better yet, a battery-free design.

I’m sorry my answer isn’t more specific, but with UPS system design, one size doesn’t fit all! There is a lot of FUD being spread by some salespeople. All the major manufacturers have some excellent products, but what might be the best design for a specific data center may not be the best for another.

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  • Dave mc
    Just some things to consider what ever UPS you select. Most modern UPS system are more than acceptable but you need to ask specific questions to see if it matches your requirements and risk profile/operational needs. As Steven G7 stated every ones needs differs and the varity of alternatives does allow you to select what is suitable. Things to consider as it is an important part of your operations; -Spare parts availability and the time taken to provide to your site – get a guarantee. - Life expectancy and parts availability, as some of the smaller units have a 5 to 8 year life span. -The number of available service personal trained in your particular purchase and are they local or do they have to fly in. – a local sub contractor may not be acceptable if not 100% trained in your box. -Service costs. - Ask where they are made – some in the past acceptable suppliers are making two products that are the same, one in the traditional proven factors and one in a developing country. Constant quality is the issue. -Is your service and repair contract with the manufacturer or is it though a third party. One of the major manufactures is only a supplier of product and I have found that the ability to get prompt service is a lottery and the costs are very high due to margin on margin for both the parts and labor. -Can the maintenance be undertaken without taking your whole system onto maintenance bypass as this may not be acceptable? Note some of the suppliers that quote hot swappable engines is not the case in all situations especially when the static transfer switch is within the same unit or the individual swappable units are of the larger size. -Your configuration design needs to be matched to the UPS you select. In relation to batteries as noted by Steven G7, you need to be careful as to what you buy, In my experience the Gel & Paste types have a lot shorter life span and often fail when needed, use only a quality valve regulated flooded acid battery. You only get what you pay for and it is a lot harder to get more capital for replacement. Ensure you get an acceptable pro-rata warranty and remember the good product sells it’s self careful of the pressure Car type sales man. As one last note you need to purchase the type of UPS to suit your operations & system configuration.. - If the UPS does not have a transformer that acts to remove some of the harmonics and spikes you need to ensure it has a dynamic harmonics filter fitted. - If the system is a single conversion bypass type it also must be fitted with a dynamic harmonics filter. - Also I have seen some systems that have a switch able battery system that saves them the larger battery charging systems (separate system) and improves their energy efficiency figures (because they can leave out the battery charger – they claim separate system) I would not recommend these as they have more things to go wrong and actually have a short break of supply and do not act a s a dampener to remove the very high frequency harmonics.
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  • StevenG7
    Excellent points, Dave mc! Regarding transformer vs. transformerless design UPSes, I reviewed some documents which have been published since my original answer in 2008(!). For anyone interested in the subject, I'm going to recommend a GE white-paper found at: Some of it is vendor specific but there is a section, "UPS technology–separating the wheat from the chaff", which has the best discussion of the transformer vs. transformerless design issues I've seen yet. Well worth reading. (Disclaimer: I have no connection with GE or any other UPS supplier)
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  • StevenG7
    For some reason the "link" feature in the editor this website uses didn't include the link, so here it is: http://www.gedigitalenergy.com/products/applications/PowerQuality/The%20Digital%20World%20and%20Electric%20Power%20Supply%20-%20A%20Hypersensitive%20Imbalance.pdf
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