Inverter of UPS fails

We have three phase two UPS of 30KVA each in parallel operation. From the last four months inverter fails problem arises in each of UPS. We checked our system thoroughly and finds out nothing. But we checked our output currents and finds out that neutral current (5.7 Amp) is higher than individual currents (4.7 Amp). Our system output neutral is not grounded and it is in floating condition.

Requires technical comments to resolve this issue.