I propose to go for a branded airconditioner (VRV technology), the tonnage is about 70 tr. It works on 3phase. I understand that it will not run when the voltage is less than 380v. But in our area at times the voltage is only 220v in 3-phase. How can I overcome this problem.

Call your utility company and have them install 3 phse lines to your house /business or get a smaller A/C cause having them run 3 phase to the building is very $$$expensive$$$