Hi Sagarsama,
So, you're requesting the same register over some period of time, and it never errors but the value is usually what you would expect for the kWh and occasionally what you expect for the instantaneous voltage? That's bizarre. I would set up a Mango reading that register for a while to be sure that is what is going on (you make it sounds as though you are using Modbus4J in your own application), but that sounds like an issue with the PLC. If you're requesting the same range of values and it is spontaneously changing those values, that is its issue.