You can find some difference between a Government Polytechnic Institute and a Private Polytechnic Institute. Both will facilitate you to gain diploma in engineering degree.The procedure are same.You are to study four years there to get the degree. But the study cost in govt. polytechnics are less then pvt. polytechnics. In some case you will have a better campus in govt. polytechnics than pvt. institutes. Getting chance to study in pvt. institutions is easier than government institutions. Remember that both will give you a degree but you have to learn by your own and prove it in job interviews that you have ideas what you have gained through that course.It sounds clear after gaining the degree you are on your own and your certificates will be the same as govt. institute even though you get the degree from private institute.