No tax on advance received by NHPC against depreciation as it was part of tariff and it would reduce

IT : Where assessee, a public sector company, engaged in selling electricity to State Electricity Boards, received Advance Against Depreciation (AAD) by way of tariff charges which was to be adjusted against future depreciation so as to reduce tariff in future years, amount so received was to be regarded as liability and, thus, not includible in computation of taxable income