Thanks for your interesting question. Could you be more explicit on your application? Anyway, I will try to bring answer for MV/LV transformer application in buildings.
Paralleling two or more transformers can be done for two main reasons: To increase the power delivered to LV system or to Increase availability of the supply of LV system (redundancy)
For a given load of a low voltage installation supplied by MV grid there are several possible architectures
- Using several smaller separate MV/LV transformers supplying several sub-systems in LV
- Using one MV/LV transformer covering all needs supplying one LV system
- Using two (or more) smaller MV/LV transformers in parallel supplying one LV system
- Using two (or more) transformers able to supply all the LV system each
I will leave aside first case. But why should we prefer one big transformer or two smaller in parallel? For example, if a building has a maximum power demand estimated around 1450kVA is it better to have one 1600kVA MV/LV transformer or two 800kVA in Parallel?
Benefits of two transformers solution:
Full redundancy is possible but in that case each transformer shall have the full power capability and in that case we lose the previous benefits. And it will rise some other questions (Active or passive redundancy, selectivity …)
Paralleling transformers requires some attention on the transformers : same winding arrangement and vector group, same transformation ratio same impedance drop. Rated power of each can be different. for detail see Schneider Electric - Square D technical note on paraleling transformers
Power System Expert - Schneider Electric
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