i gave one snubber across the coil of contactor.

Where do you have snubber across the output or input of contactor what's the contactor volage ratings for input and output? If the coil is AC and the output is AC do remember to put a snubber across the input coil of contactor as well as across the output of contactor.

I do not use supervisor ic for micro.

That's is one of the biggest mistake people do. Always use a good supervisor for professional designs in case of inustrial process control it is even more critical. DS1232, ADM1232 is easily available here in India. If you don't want to use extrernal watchdog and want to inhibit ALE for EMI reduction you can use MAX812 availbale throug RS.
Hi Haribabu,


out of three phase supply, one phase is given for
contactor coil through relay ( 24V optocoupler used )
and another phase for smps.

Be carefull with the PCB track routing around the optocoupler never make the mistake of running track under the opto. Always keep all the output and input signal to opto totally separate and far away from each other. Never route them close to each other.

but yet the problem is not solved.

What snubber are you using what's the configuration. I mean value and ratings of R and C.

Although nothing dowith your problem but will you please tell me what regulator are using for 3.3V.

Regards,
Prahlad Purohit