Accounting and Settlement of Secondary Reserve Ancillary Services in Indian Power System

Automatic Generation Control (AGC) plays a crucial role in maintaining the balance between electricity generation and demand in the power system. Pan India, 24x7 AGC implementation started on 21st July, 2021, and presently includes 70 power plants, with a total installed capacity of 67,337 MW. To ensure the proper functioning of AGC, energy accounting, performance assessment, and incentive calculation are essential. The end-to-end aspects of implementing AGC in India were explained in the paper presented at the CIGRE 2022 Kyoto Symposium [1], titled “Infrastructure and Setup for Automatic Generation Control in the Indian Power System.” In continuation, the present paper provides in-depth details on AGC accounting and settlement building on the continuous operation experience of AGC on a large scale.

Energy accounting involves tracking the AGC Up (MWh) and AGC Down (MWh) regulation dispatched for secondary frequency control. As of 29th October, 2023, a total of 5628 GWh of AGC Up and 10821 GWh of AGC Down have been dispatched. These values represent the amount of additional energy generated or backed down by the regulating resources under AGC to maintain system frequency and tie line flows within acceptable limits, by utilizing the available power reserves.

Performance assessment is another crucial aspect of AGC accounting. It involves evaluating the performance of AGC providers based on the input signal command and the response of the AGC Provider. A simple and transparent method has been adopted to subsume the effect of various parameters such as response time, accuracy, and deviation from the set point, that are typically considered in evaluating performance of a power plant. AGC providers are eligible to receive incentives up to ₹0.5/kWh based on their performance. AGC providers in India have earned ₹721 crore Indian rupees as incentives, for the services offered towards secondary frequency control.

Central Electricity Regulating Commission (CERC) notified CERC (Ancillary Services) Regulations in January 2022, and the concept of AGC was adopted as SRAS (Secondary Reserve Ancillary Services). Following the CERC Regulations, the National Load Despatch Centre (NLDC) developed a detailed procedure for SRAS implementation in December 2022 [2],[3]. Under this procedure, SRAS energy accounting, performance assessment, and incentive calculation are performed on a weekly basis using SCADA data. Indian Electricity Grid Code 2023, included secondary and tertiary reserve ancillary services, and operationalized the same through approved detailed procedures after stakeholder consultation [4][5]. Any new power plant is allowed to operate under AGC 24x7, only after the accounting process at plant end is streamlined and the data generated during open loop testing is verified.

The accounting and performance evaluation process includes the following salient activities - Signal exchange, archival, retrieval, data verification by a customized accounting software, energy accounting, performance evaluation, incentive calculation, disqualification, and requalification. The end-to-end process of AGC accounting and settlement in the Indian power system, as well as the rationale behind each of the method or the process adopted, is explained in detail in the paper. The accounting process is guided by clear regulations from CERC, and detailed procedures are documented and transparently placed in the public domain by NLDC. Resilience and sustainability have been ensured in the accounting process adopted. Some practical problems encountered during the AGC accounting process are presented as case-studies in the paper. Factors that contribute to the resilience of the SRAS accounting process viz., low financial risk, self-sustained pool account, seamless addition of the participants in the ancillary services, transparency, cybersecurity, competition, documented rules and regulations are also suitably explained in this paper.