Addressing Intermittent Over Current Faults in Dual UPS System

[jtweedie@atdesk.com]

I have two UPSs, UPSA & UPSB, and two static transfer switches, STSA & STSB. UPSA feeds Source1 on STSA (preferred) and Source1 on STSB. UPSB feeds Source2 on STSA and Source2 on STSB (preferred). Each UPS has approxiamately a balanced 15KW load. Each UPS has 4 downstream transformers.

Question: IF i fail source1 on UPSA, STSA will will transfer from source1 to source2. BUT UPSB's inverter will fault on over current. The same thing will happen if i fail the preferred source of UPSB. This problem is also intermittent on both UPSs

There is more info but i would like to see what questions are generated so i will hold off. This is the core problem.

Any ideas

 

[anorlunda]

Question: IF i fail source1 on UPSA, STSA will will transfer from source1 to source2. BUT UPSB's inverter will fault on over current.

This seems to make no sense. If B will trip on over current, then B is not adequately sized to carry both loads. No switching arrangement will cure that. You must have two UPS systems, each rated to supply A+B loads.