Hi All,
Abhaysk, Thanks for the support. Finally i got the hint from dba_waiters joining v$session and v$sql. It was series of update query updating same table, which was blocking all the sessions in application flow. It has been re-written and now the redo generation back to normal. 3 Hrs/switch average. Logminer too shown the same statement which helped me to narrow down to the issue.

Thanks