While writing an selinium test I came across an problem while adding text to the ckEditor instance thorugh the test. And after a long search and research I got the below solution.

Command works is runscript() :
Usage : runscript(script);
Example :
runScript(CKEDITOR.instances["edit-body"].setData('<p>testContent</p>'); );

where "edit-body", is the instance name of the loaded ckdeditor.

Hope this helps someone. :)