Master guard UPS . Inverter Backpower Alarm. 1

[noshad]

Hi friends.

We have 1 UPS which has following details.

Make : Master guard (Emerson) Series "E"
Rating: 6KVA
Single phase input/output 230VAC. 50 Hz

Today one alarm came "INVERTER BACKFEED" on display of UPS and UPS gone to Bypass mode. We reset the fault and again make it online . It work for 6 hours and same alarm came "INVERTER BACKFEED" and Ups gone to bypass mode. Reset the fault and UPS working normal again.
after reset follwing Measurements coming on UPS Display.
Input voltage : 237 V
Input Frequency : 49.9 Hz
Output Voltage : 230 V
Output Frequency : 49.9 Hz
Output Load : 33 percent
Output Current : 5 Amp
Output Watt : 1391 W
Output VA : 1468 VA
Batt Volt : 273 V
Batt Cap : 100 Percent
Backup : 39 min 47 sec
Positive DC bus : 361 V
Negative DC bus : 361 V

I tried to search at google regarding this fault but cannot find any information.

what is " Inverter Backfeed" Alarm? and what is the remedy for this type of alarm.

Advance Thanks.
I am working in a petrochemical plant. And this UPS is used for control power (PLC, and other control equipments)

 

[ScottyUK]

Not knowing that specific UPS model, I think the fault is that the inverter is delivering power back through the static bypass switch and/or maintenance bypass.

A similar alarm from the GE Sitepro which I do know quite well:

"Back-feed Protection
All SitePro UPS's are equipped with an automatic system for the protection against voltage back feeding towards Utility, through the bypass (Applied Standard IEC 62040-1).
This protection works automatically by opening contactor K6 (in series with the thyristors of the static switch) and eventually K7, and acts in case of internal defects of the system, or due to wrong manipulations on the maintenance bypass Q2."