Settings of connection timeout for Oracle database
There is no client setting that would cause a connection to be dropped leading to an ORA-03113 error after some time. And there is no setting on the database server that would cause a connection to be timed out leading to an ORA-03113 error.
The server can enable dead connection detection (DCD) by setting the sqlnet.expire_time setting in the server's sqlnet.ora. That will cause the server to periodically send a probe packet to verify that the client is still up.
Oracle will never drop a connection due to inactivity with an ORA-03113 error. It is possible to configure Oracle to drop idle connections but that would generate a different error. If you are getting an ORA-03113 error, either the firewall is causing the connection to be dropped or there is some other hiccup in the network between the client machine and the server.