S. 80IA : Industrial undertakings-Enterprises engaged in infrastructure development-Market value-Captive power plant-Power supplied to own units-Rate to be adopted at which assessee supplies surplus power to State Electricity Board-Not determined in normal course of Trade and competition but under statutory contract. [S. 80IA ((4) (iv) 80IA(8), Electricity (Supply) Act, 1948, S. 43, 43A 44]