While Transmitting the high voltages from Grid stations the voltage is kept very high and current is kept Low. Doesn't it negates the Ohm's Law V=IR

To avoid impedence losses(i2x) in long transmission lines, current is reduced, which is only possible by increasing the transmission voltage.(power being constant). This is done by using a transformer, which provides an efficiency of around98%.  Ohms law is not applicable for Transformers.

because we transmute KVA in high distance transmission line , so we use start up transformer to up voltage to keep ampere too low to reduce lost in cable ,

the main good is reduce lost in transmission cable so we decrees ampere and increase line cross section 

 Transformers do not obey ohms law........the input power in a transformer is equal to the output power, that's why when we step up voltage current is decreased.

Ohms law is applicable in case of purely resistive loads (R). The transformer constructed with windings on primary and secondary sides are inductive in nature. Hence Ohms law is not applicable to transformers.