Section 2(1)(f) in The Delhi Electricity Regulatory Commission (Terms and Conditions for Determination of Transmission Tariff) Regulations, 2011
(f)"Availability" in relation to a transmission system for a given period means the time in hours during that period in which the transmission system is capable to transmit electricity at its Rated Voltage and shall be expressed in percentage of total hours in the given period, and shall be calculated as directed by the Commission;