Minimum clearance will be defined by the Std in force where the installations will be built. Where are you working? In Canada for example we mostly use IEC standards with some adjustments for local conditions like snow cover reducing clearance to ground in winter. In some locations it is not clear which std is in force and for such cases, I will try to implement the safest one. You will also have to consider usage like drive path for vehicles that might add some additional clearance (ex: trucks moving inside a substation between a building and live lines will require some more clearance).