page_title: Availability-based tariff
section_title: ABT drawbacks
hierarchical_section_title: Availability-based tariff / ABT drawbacks
context_page_description: Availability Based Tariff is a frequency based pricing mechanism applicable in India for unscheduled electric power transactions. The ABT falls under electricity market mechanisms to charge and regulate power to achieve short term and long term network stability as well as incentives and dis-incentives to grid participants against deviations in committed supplies as the case may be.
context_section_description: As per DSM / UI procedure, the incentives and penalty to the grid participants are charged based on the average grid frequency in a time block of 15 minutes duration. During a time block, it is normal that frequency goes above rated 50 Hz frequency and comes down below rated frequency as the number of frequency excursions above 50 Hz are more than 100 in a day. Thus the average frequency in a time block remains close to the 50 Hz without giving much benefit in the applicable UI tariff for a Discom who is consuming the surplus power available in the grid or generators with valid scheduling who is reducing the generation when frequency is above 50 Hz. Similarly, the generators and Discoms who are not adhering to grid discipline are not penalised with UI tariff in excess of normal tariff when average grid frequency in a time block is used for fixing UI/DSM charges. Each time block is further needs to be separated into two parts for application of UI charges. One for the duration the frequency is more than 50 Hz whose average frequency is considered for fixing UI/ DSM charges to consume the excess power in the grid or reduce excess power generation. Another for the duration the frequency is less than 50 Hz whose average frequency is considered for fixing UI/DSM charges to reduce over drawl and encourage additional power generation.
  Whenever distribution feeders from a substation are switched on after a break down or scheduled power cut, it should be done only when grid frequency is above 50 Hz such that it does not lead to steep drop in the frequency . The total numbers of feeders switching on, in a day are substantial at national level to cause load (≥ 500 MW) increase on the grid to cause wide fluctuations.
  The incentives and disincentives are prefixed  (annually/periodically) by the electricity regulator (CERC) for the variation in the grid frequency which may not reflect the actual situation temporally and spatially on day-to-day basis. There is a need to decide the electricity tariff by the grid participants (generators, discoms, transcos & final consumers) on day-to-day basis for achieving further fine tuning. To correct these anomalies, CERC has proposed 100% sale and purchase of power produced in day ahead market.
  The ABT mechanism aims to maintain grid frequency at 50 Hz but does not permit the grid participants to decide the optimum frequency within the permitted frequency band (say 49.20 to 50.80 Hz) on day-to-day basis. This is required not to impose additional load shedding/power cuts when frequency is within the safe variation limits.
  Transmission system operator (TSO) is obliged to provide non-discriminatory transmission access to electricity generators and consumers in order to promote competition. ABT mechanism does not bring at par all the grid participants whether in private or central sector or state sector ownership.  ABT mechanism does not encourage to install the generating units at advantageous locations to offer least cost electricity to the final electricity consumers. ABT mechanism is suitable in an electricity grid suffering from perennial power shortages to prevent overdrwals but it is not suitable for the grid with surplus electricity generation with non-discriminatory responsibility. CERC regulation on ancillary services operations, are permitting only inter state power generating stations to provide these services which are discriminatory by not allowing rest of electricity generators.
  Every state is conducting independently load management to avoid overdrawal from other states by using mix of generation sources (ex: hydro power or peaking power plants) to adhere to their power drawal commitments on 15 minutes period basis in ABT mechanism. Thus hydro power stations are ending up to cater base load instead of peak load in non-monsoon months also (ex: Kerala, Karnataka, Telangana, HP, J&K, Uttarakhand, etc.). TSO is responsible to ensure the provision of reserves  (including spinning reserve for base load power plants by operating in frequency follow mode with upper & lower generation caps) tha
caption: An idealized representation of the four kinds of reserve power and the time intervals after an unexpected failure that they are in use.[23]
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