Finance, Property, Contracts
Unless Parliament provides otherwise, a state cannot tax electricity consumed/sold to the Government of India, or consumed/sold for railway construction/maintenance/operation - and any state tax on electricity sales must ensure the Government of India (or a railway company) pays less than what's charged to other large consumers.
This protects the Union government and railway operations from state electricity taxes, and specifically requires that even where such taxation exists for private use, government/railway consumption gets a discounted rate compared to ordinary large consumers.
This is why electricity consumed for railway operations across India generally isn't subject to the same state electricity taxes that apply to ordinary large industrial or commercial electricity consumers.