using ATS on output of UPS for bypass

[eddie11]

I am wondering what the opinions are out there of people who do this more for a living. I know a service provider that needs high availability. Because some site are unattended, they protect against UPS failure by putting an open transition, standard mechanical-transfer ATS on the output side of the UPS. The critical load is a data center floor with lots of servers.

It seems to me that this replaces the single point of failure of the UPS with a non-maintainable single point of failure. I don't think this is a good idea.

does anyone else believe in doing this?

 

[ScottyUK]

Hi Eddie,

Many of the larger commercially-available systems have a static transfer switch (STS) to provide a no-break transfer from inverter to a bypass source. They may have an additional manual bypass in parallel with the STS to allow the unit to be shut down while continuing to provide power to the load, although clearly in this mode there is no UPS backup should the mains fail. All the preceding transfers do not need to cause interruption of power to the load.

There are installations which provide a 'disaster recovery' capability by which the entire UPS and transfer switch can be disconnected and power re-routed directly to the load. This can be done without interruption provided that the unit is already in its internal bypass mode. We provided this facility at our plant to allow supplies to be restored in the event of a total loss of our redundant UPS through, say, a fire within the UPS room. The switchgear is in a separate room.





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[alehman]

An open transition transfer switch is typically too slow to allow uniterrupted operation of the servers. You could use a closed transition ATS. I agree with your comment about the ATS being non-maintainable and another possible single point of failure.