Lighting in Mining Area

Dear Sir, As per Indian Electricity rule surface mining area and open cast mining area power supply for the lighting shall not be exceed 250 V (L-L) and neutral point shall be solidly earthed. I have 415 V, 3 Phase supply, to fulfill the above requirement I have to use 415/240 V (L-L) 3 Phase transformer. Why this is required? what are advantages of this system. Instead of above can I use 415/415 V lighting transformer? In that case lighting supply will be 240 v (L-N). Thanks