States Escape CERC Rap for Power Overdrawal with Warning to Ensure Grid Stability

SRLDC claims the grid frequency dropped below the prescribed limit, reaching as low as 49.4 Hz

September 14, 2023


The Central Electricity Regulatory Commission (CERC), in response to a petition filed by the Southern Regional Load Despatch Centre (SRLDC) regarding critical operational challenges of the grid in South India, has directed the states to provide quarterly progress reports to SRLDC on action taken to ensure grid stability.

However, CERC refrained from imposing any penalties on the states for now but directed SRLDC to approach the Commission if it encounters issues with action plan implementation or non-compliance with directives.


SRLDC filed a petition regarding critical operational challenges faced by the electricity grid in South India from February 1, 2022, to April 20, 2022.

During this period, the grid’s frequency dropped below the prescribed limit of 49.90 Hz, reaching as low as 49.4 to 49.7 Hz, posing a significant risk to grid stability. The frequency remained below 49.90 Hz for a cumulative duration of 290 hours during this period.

Factors contributing to these challenges include high irrigation load, rising temperatures, increased electricity demand, supply-side constraints like low fuel supply, reduced hydro reservoir levels, planned outages, and low reserve capacity.

SRLDC claimed massive overdrawal from the grid exacerbated the situation, leading to prolonged periods of low-frequency operation. Any tripping or incident during these conditions could have resulted in a major disruption or disturbance in the grid.

An example cited occurred on April 20, 2022, at 15:47 hours when a loss of 1,300 MW of thermal generation at SEIL – P2 (in the Southern Region) caused the grid frequency to fall from 49.72 Hz to 49.61 Hz, a significant drop of 0.11 Hz.

SRLDC sought penalties on the states for non-compliance, ensuring generation adequacy and adequate reserves.

It also wanted proper forecasting of demand and renewables, implementing an action plan for operationalizing the revised Advanced Distribution Management System and Physical Regulation, enhancing coordination among hydro generation, agriculture load segregation, and load-side ramp-up/down limits, and augmenting intrastate transmission systems.

State-wise Figures

Andhra Pradesh consistently overdrew power from the grid, with overdrawal levels ranging from 400 MW to 1,200 MW during various time blocks. This overdrawal occurred even when the grid frequency fell below the permissible limit of 49.90 Hz.

Andhra Pradesh has been drawing electricity from the grid in excess of its scheduled or allocated amount. This overdrawal ranges from 0.3% to 5.4% of its daily energy consumption. On a daily basis, this overdrawn energy can vary between 1 to 9 MUs. In addition to overdrawal from the grid, Andhra Pradesh also meets a significant portion of its electricity needs by purchasing power from various segments of the short-term electricity market.

From February 1, 2022, to April 20, 2022, SRLDC issued Andhra Pradesh 313 warning messages pertaining to alerts, 291 related emergencies, and 244 for non-compliance.

Karnataka overdrew electricity in the range of 0.5 MUs to 6.3 MUs per day during the considered period. The state met 0.2% to 2.3% of its daily energy requirement through grid overdrawal.

Karnataka also sold in the range of 2% to 48% of its schedule, i.e., 4 to 31 MU per day in the short-term market. This short-term sale by Karnataka in the range of 0.03 to 4.3 MUs was made in the same period in which Karnataka was significantly overdrawing, and the grid frequency was persisting below the lower limit of the IEGC specified band.

Karnataka was issued 248 warning messages pertaining to alerts, 208  about emergencies, and 182 were issued for non-compliance.

Tamil Nadu overdrew electricity in the range of 2 to 9 Mus and met approximately 16% to 37% of its schedule by buying electricity from the short-term market segments, which include STOA-bilateral, day-ahead market (DAM), and real-time market (RTM).

The state met a significant portion of its schedule by purchasing electricity from various segments of the short-term electricity market.

Tamil Nadu received 132 warning messages pertaining to alerts, 175 emergencies, and 144 non-compliances.

Ineffectiveness of Automatic Demand Management Scheme

ADMS was implemented to alarm when the grid frequency fell to 49.9 Hz or below, indicating overdrawal above 250 MW (150 MW for Kerala) for 10 minutes.

Automatic tripping of identified feeders through ADMS occurs when the grid frequency drops to 49.85 Hz or below, indicating overdrawal above 250 MW (150 MW for Kerala) for 15 minutes.

The implementation of ADMS proved to be ineffective. From January 1, 2021, to April 20, 2022, there were 246 instances of ADMS activation. However, load relief was observed only in 145 instances (approximately 59%), with an average relief of about 43 MW. This means that ADMS did not provide the desired relief in most cases.

Actions Taken by SRLDC

The revised ADMS has been proposed in response to the inadequacy of the existing program in managing overdrawals. The revised ADMS introduces different stages of load disconnection, and each is triggered based on specific conditions related to grid frequency and overdrawal magnitude.

Each state in the Southern Region is required to identify specific groups of load feeders for use in Stage 1, Stage 2, and Stage 3 of the ADMS. These feeders are designated for load disconnection in response to overdrawal events.

SRLDC has proposed and advised constituents to implement the revised ADMS starting April 17, 2022.

SELDC also proposed a three-stage emergency control measure to manage overdrawals where grid frequency drops sharply, typically during low-frequency conditions.

Proposed Measures to Avoid Recurrence

The petition outlines several important recommendations and actions that need to be taken by the states and relevant authorities to address the issues related to grid stability and over-drawal:

  • Avoiding Heavy Reliance on Day-Ahead and Real-Time Markets (DAM & RTM): States should avoid relying heavily on the DAM and RTM to meet their rising peak power demands. Heavy reliance on these markets can lead to high prices and make state utilities resort to over-drawing from the grid, jeopardizing grid stability.
  • Demand Estimation and Management: States must improve their demand estimation processes for different time horizons as specified in the Indian Electricity Grid Code (IEGC). Timely implementation of demand management measures, such as the ADMS and Load Trimming programs, is crucial to avoid over-drawal during real-time grid operation.
  • Better Coordination for Ramp Management: Mismatches in generation and load ramps, particularly in renewable energy-rich states, can lead to grid instability. Properly coordinating hydro unit operations and load staggering plans during ramping hours is essential to avoid significant deviations from scheduled power flows.
  • Improved Renewable Energy Forecasting and Scheduling: States should enhance their forecasting infrastructure to predict demand and renewable energy generation better. Dedicated Renewable Energy Management Centres can be vital in improving coordination with renewable power stations to enhance forecasting accuracy.
  • Addressing Generation Adequacy: States must ensure generation adequacy based on their forecasted demand by reviving generating units out of operation for economic reasons. SLDCs should also ensure the availability of reserves through periodic unit commitments.
  • Fuel Security and Adequacy Statements: States should periodically review supply-side issues and work with appropriate agencies to ensure fuel security for their generators. Preparing quarterly generation adequacy statements can help address deficit scenarios in advance.
  • Augmenting Intra-State Transmission Systems: States need to plan and augment their internal networks to handle scenarios caused by low internal generation and heavy over-drawal. States should also declare and monitor available transfer capacity and total transfer capacity violations on their websites.
  • Reserves and Ancillary Services at State Level: States should maintain necessary spinning reserves through periodic unit commitments. They should also implement the recommendations outlined in the ‘SANTULAN’ report, which provides modalities for a framework for intra-state reserves and ancillary services.
  • Utilizing Pumped Hydro Power Stations: Pumped hydro storage units can provide peaking and ramping reserves to manage imbalances. Non-operational units in pump mode should be made operational as soon as possible.

Karnataka State Load Despatch Centre (KPTCL) has provided information regarding the resource adequacy and peak demand requirements from April 1, 2022, to March 31, 2023. According to their data, the ex-bus availability of power (without Short-Term Open Access or STOA) for April 2022 was 14,608 MW. This exceeded the ex-Bus unrestricted requirement of 14,583 MW, resulting in a surplus of 25 MW for April 2022.

KPTCL emphasized that the state of Karnataka relies heavily on Long-Term Power Purchase Agreements (PPAs) with power generators to meet its electricity demand. This indicates that a significant portion of Karnataka’s power supply is contracted through long-term agreements with power producers.

KPTCL explained that their ADMS tripping is configured according to recommendations from the State Load Despatch Centre (SLDC) in Karnataka. It operates in a round-robin manner for tripping 11 kV feeders, as per the list provided by Electricity Supply Companies (ESCOMs). They also mentioned an expected relief of 2,362 MW when the ADMS system is activated.

Tamil Nadu Transmission Corporation (TANTRANSCO) has outlined the settings for its ADMS related to frequency and quantum (amount of power).

TANTRANSCO has reported that during the period from February 1, 2022, to April 20, 2022, there were no Low Voltage Ride Through (LVRT) or High Voltage Ride Through (HVRT) events related to tripping due to renewable energy sources (RE).

Transmission Corporation of Andhra Pradesh (APTRANSCO) has reported the evening peak demand for electricity in Andhra Pradesh during different months. In February 2022, the demand varied from 7,400 MW to 8,400 MW; in March 2022, it ranged from 9,000 MW to 9,500 MW; and in April 2022, it varied from 8,500 MW to 9,000 MW. These figures reflect the fluctuating electricity demand during peak hours.

APTRANSCO noted that during the mentioned period, power availability from state thermal plants did not align with the forecasted availability due to factors such as coal quality and availability. To meet the state grid demand, APTRANSCO had to rely on power exchanges in both the Day-Ahead-Market (DAM) and Real-Time-Market (RTM).

In February 2022, the distribution companies of Andhra Pradesh (APDISCOMs) were temporarily barred from trading in the power exchange due to non-maintenance of credit margin. Subsequently, in March 2022 and April 2022, APDISCOMs procured power amounting to 521 MU and 546 MU, respectively, through the DEEP (Discovery of Efficient Electricity Price) e-bidding portal.

APTRANSCO pointed out that there has been a significant increase in economic activity post the COVID-19 pandemic, leading to a surge in electricity demand beyond what was anticipated. Due to these challenges, APTRANSCO had to implement load relief measures across the state during February, March, and April 2022, amounting to 71.23 MU, 64.645 MU, and 366.49 MU, respectively.

Tamil Nadu State Load Despatch Centre (TNSLDC) explained that, due to the formation of the ONE GRID in India, the grid frequency is common for all states and regions in India. It noted instances where they had overdrawn more than 250 MW when the frequency was less than 49.90 Hz. In contrast, they also had instances where they had underdrawn less than 0 MW under similar frequency conditions.

TNSLDC explained that they use the Kadamparai Hydro Pumped Storage Station in both generator and pump modes to provide peaking and ramping reserves.

Karnataka Power Transmission Corporation (KPTCL) highlighted several key points. It emphasized Karnataka’s significant renewable energy capacity, comprising solar, wind, and other sources, accounting for 51% of the total generation capacity. KPTCL mentioned challenges in managing RE variability and the need to keep thermal generators on standby to balance the grid.

It argued against allegations of selling power during shortfalls and pointed out the complexity of forecasting RE generation accurately. KPTCL presented data on grid frequency profiles, noting both overdrawal and underdrawal situations, which they argued were critical for a comprehensive grid assessment. The submission discussed issues related to hydel generation during irrigation periods, limited primary and secondary response capabilities, and fluctuations in block-wise deviations.

Commission’s Analysis

The Commission noted that during a specific period, certain states, including Tamil Nadu, Karnataka, and Andhra Pradesh, continuously overdraw electricity from the grid. This led to the issuance of numerous alert, emergency, and non-compliance messages by the SRLDC. Continuous overdrawal can strain the grid and pose a risk to its security and reliability.

The states provided several reasons for the overdrawal, including variations in renewable energy generation, deviations in generation and demand forecasts, increased energy consumption, coal shortages affecting power generation, non-availability of power at power exchanges, and other operational challenges.

In response to the overdrawal issue, the SRLDC convened meetings with the SLDCs and finalized an action plan. This action plan included measures related to demand estimation, generation resource adequacy, fuel security, demand management, and more. SLDCs were directed to take specific actions to ensure compliance with the regulations.

The communication between RLDCs and SLDCs includes alert, emergency, and non-compliance messages. It was noted that the non-compliance messages lacked clarity in specifying which activities or directions were not being followed. The Commission noted that clear and specific communication is essential for addressing grid issues effectively.

The message formats used for communication between RLDCs and SLDCs did not include the prevailing grid frequency, suggesting that grid frequency be included in messages to convey the severity of the situation.

Despite the continuous overdrawal issue, the Commission decided not to levy penalties. Instead, it directed the states to adhere to the action plan and submit quarterly reports on its implementation. If issues persist, the petitioner is encouraged to approach the regulatory authority.

In February, CERC issued guidelines to supplement the Deviation Settlement Mechanism (DSM) Regulations 2022 to maintain grid security. The Commission has added a new category of wind-solar generators and introduced charges for DSM. Further, it has also hiked monetary incentives for both generators and procurers to maintain the grid frequency between the safe range of 49.95-50.05 Hz.

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