thank u sir for your answer..
Actually i compared the  results i got from Ansys simulation with
Intellisuite and some analytical formulas from some papers for simple beam
structures. For deflection the  results were in in good aggrement. But
when I took single comb drive my results are not matcing witheither
coventer or intellisuite, even with an analytical formula given in a
paper. So in this case i used 3D air meshing around the comb but
result(capacitance) is too high..  If you can get any clue please let me
know..
Thanking you once again..

Regards,
Satish. Goravar