Paralleling of Transformer

What is the probability of simultaneous failure of both UPSs?

If a UPS has failed, then isn't it really an IPS?

you need to consider frequency+vector group+voltage rating also for the intended transformers, not only the impedance

Conditions for parellel operation are,
Same voltages at two sides, vector group and impedance ratio is must for parellel operation of transformers.
The load is shared between two transformers according to its kVA
If UPS 1 failed you have UPS2
If UPS1 and 2 failed you have Transformer 1
If UPS1 and 2, Transformer 1 failed you have Transformer 2
So select the transformer size for any failure
If UPS 1&2 and Transformer 1 & 2 failed you have nothing

If he himself failed then ?

In case of Parallel UPS Architecture (Whether for Capacity OR Redundancy); the Automatic Bypass Supply to the Paralleled UPS Output Bus (2X200 KVA in ur case) should be fed from single transformer and not two independent transformers i.e. 200 KVA bypass transformer rating is required if the Paralleing of UPSs is done for Redundancy and 400 KVA bypass transformer rating is required if the paralleling of the UPSs is done for Capacity.

The architecture conceptualized / installed by you is not recommended considering variations in the impedenace of cables/lug-contacts, switchgears etc.

Rgds

Sanjeev

Thanks , Paralleling is done for redundancy purpose only , and transformer connected separately is also to achieve redundancy . ( I.e if one UPS along transformer fails , very very rare occurrence )

Thanks for your reply

Sudhir199,

I understood you will be using this redundant UPS system for extremely critical loads. You didn't provide the detail configuration of the UPS system and I assume each of the bypass transformers is connected to the individual UPS and there is static transfer switch to transfer the load to/from the bypass transformer and both of the UPS systems are synchronized. In case of the both UPS's fail (very rare scenario though but is considered for extremely critical loads such as hospital ICU), the bypass transformers supply the power to the load.

Are both of the bypass transformers fed from same source or different source? The extreme redundant nature of your UPS made me feel they are from different sources. If they are from same source, then you are right – the load will be shared by each transformer depending on their impedances including the cable impedances (if cable length differs significantly). If they are from different sources, then the load will be shared by each transformer depending on their impedances (including cable impedances) and differences of the voltages (though it is very small) of the two sources.

- MS

Thanks for reply ,

2 different sources used for bypass supply.As load connected to UPS systems are veru very critical user would like to go for such type of configuration .