My project have 600v 800V disconnector with neutral,From this disconnector I have 300KVA transformer(600/208,triangle/y),My question is : Do I have to run transformer ground wire to building common grounding system,if I have to ,what is wire size ?

Sounds like homework to me.

Here we go again.

If it is not homework, you should get someone to do the job who knows what they are doing.