is inter state supply need sapperate registration under GST like casual person????

As per Section 22 Of The ACT Reads As 'Every Supplier Shall Be Liable To Be Registered Under This Act In The State Or Union Territory, Other Than Special Category States, From Where He Makes A Taxable Supply Of Goods Or Services Or Both, If His Aggregate Turnover In A Financial Year Exceeds Twenty Lakh Rupees,

PLEASE NOTE FROM WHERE....MEANS WHERE HE IS REGISTERED"

Hence the state in which you registered can make supply to any where in the country

no you are not required but you are required to issue igst bill instead of sgst and cgst

(if I am registered in Kerala 
I wanted supply for Tamil Nadu ...(inter state supply )


If You will supply from Kerala to Tamilnadu (or any of the State / Country) then no need to take Registration under Tamilnadu.

But, In case You will supply from (in) Tamilnadu then Registration is required.