DC bus overvoltage

[Anonymous user]

Hi,

we are using several UPS SRT6KRMXLI connected to a transformer taking power from a 25KV AC  monophase power source. 

We are facing an error "DC bus overvoltage"  as described in the log registry of the events that require a manual reset of the UPS. Manual imply an physical intervention on the machine that is normally abandoned on a "difficult to reach" location.

After this problem occurs several times a 118 error that required a first replacement of the unit oblige us to replace the unit.

APC agree to replace the unit under warranty because after having back the device they detected a damage to the internal "Uninterruptible Power Supply Unit" in other words they are convinced it is a defective unit.

Now after replacement we have the same problem again and thinking that it could be related to voltage peaks in the primary power line transferred to the secondary 220V line by the transformer.

Our question is:  What could cause the above mentioned "DC bus overvoltage 118  error" ?

We think this answer could give us a clue on how to protect the UPS

Many thanks,

Gianluca