Can we have OPC server of the Plant Scada installed on a separate server while the SCADA core application is running on different server?

As Michael mentioned, this is possible. You simply define what machine the OPC Server will run, which can be different from the SCADA core processes (like Trend, IO, Alarm, Report, etc.).

The OPC DA Server becomes an IO Client, and will connect to any local or remote IO Servers to fetch the data requested.

You make this change in Plant SCADA Studio, within the Topology Activity, under Edit > OPC DA Servers, then modify the Network Address to match the machine you want it to run on.

As Michael mentioned, this is possible. You simply define what machine the OPC Server will run, which can be different from the SCADA core processes (like Trend, IO, Alarm, Report, etc.).

The OPC DA Server becomes an IO Client, and will connect to any local or remote IO Servers to fetch the data requested.

You make this change in Plant SCADA Studio, within the Topology Activity, under Edit > OPC DA Servers, then modify the Network Address to match the machine you want it to run on.