I'm very confident that there is a reasoning to swap the poles from DC configuration to AC. The old caternary system used in Kolkata and Mumbai region was brought by British Railway. But we were much more quicker to decide on using AC as primary source than UK itself. So majority of IR tracks of AC configuration poles in them. Like I said that they are swapping old DC poles with the new AC poles is not just an Indian regional thing but it's happening in UK as well. So we just need to find that techinal reason.