CEA committee finds no significant damage from thermal plants operating at 55% MTL

A committee constituted by the Central Electricity Authority (CEA) to assess the wear and tear, operation and maintenance (O&M) requirements and plant lifespan implications of flexible and two-shift operation of thermal power plants has concluded that no significant damage can be attributed to operation at 55% Minimum Technical Load (MTL) with conservative ramp rates. The committee, chaired by Shri B.C. Mallick, Principal Chief Engineer-II, CEA, was constituted following a meeting chaired by the Secretary (Power) on May 27, 2025, where NTPC raised concerns over two-shift operation and 40% load flexing and their potential impact on unit health.

The committee examined operational data provided by NTPC for Farakka Unit-2 and Jhajjar Unit-3, both rated at 210 MW. Farakka Unit-2 is 39 years old, while Jhajjar Unit-3 is 13 years old. The analysis found that neither unit operated below 55% MTL under normal conditions and that their ramp rates generally remained conservative, at less than 0.5% per minute.

Operational impact

Based on the available data and empirical evidence, the committee concluded that approximately 70% of the observed issues were not attributable to flexible operation. Instead, the issues were linked to ageing, poor coal quality, operational disturbances, start-up and shutdown procedures, and human or procedural errors.

The committee also cautioned against averaging failures across the entire thermal fleet, stating that such an approach is not scientifically valid because individual units differ in age, operating history, maintenance standards and coal quality. Units operating beyond their design life naturally experience higher failure rates, a pattern represented by the “bathtub curve”.

BHEL, the original equipment manufacturer (OEM) representative, submitted that flexible operation results in greater life consumption than baseload operation, but said these impacts can be effectively controlled and mitigated where generating units are suitably upgraded through advanced control and retrofit solutions. BHEL identified three components of damage associated with flexible operation: damage resulting from historical operating profiles, damage arising from grid balancing requirements and additional damage from the current flexible operating regime.

BHEL further noted that frequent load cycling under grid-stabilising mechanisms such as Automatic Generation Control (AGC) and Security Constrained Economic Dispatch (SCED), including V-type, W-type and M-type ramping patterns, is more detrimental to equipment than steady operation at low load. However, utilities continue to undertake such load changes because they are compensated for them, without fully accounting for their potential damage to equipment.

Key findings

The committee found that frequent, high-magnitude ramping, rather than minimum load levels, is responsible for severe wear and tear in coal-based power plants. Consecutive load ramps without stabilisation periods create additional system disturbances and increase stress on critical components, while operation at 40% load is operationally less damaging than repeated Reserve Shutdown (RSD) cycles.

The concept of 40% MTL was first initiated by a Task Force Committee in 2017 headed by the then Director (Operations) of NTPC. The committee had recommended implementation of 50% MTL within two months and 40% MTL within six to 12 months. The report was subsequently accepted by the Ministry of Power.

The CEA’s Flexible Operation Regulations, 2023, which mandate a phase-wise reduction to 40% MTL by 2030, were based on successful countrywide pilot studies conducted since 2018 in association with international partners and OEMs.

Two-shift operation

The committee said pilot studies for two-shift operation are essential given the present grid scenario and large-scale curtailment of renewable generation. The CEA has already identified 151 coal-based generating units with a combined capacity of 34.5 GW and an age of 35 years or more for two-shift operation by 2030. Since the capital costs of these units have been fully depreciated, the committee considers them economically well placed to provide peaking power.

Data from the 5×210 MW Tuticorin Thermal Power Station, which is already operating in two-shift mode, showed that the tariff would increase by approximately 62-80 paise/kWh depending on capex requirements. The renewable integration cost was estimated at Rs. 1.46-1.60 per kWh. By comparison, equivalent battery energy storage capacity of 24 GW would cost approximately Rs. 1,88,496 crore, while retrofitting the 151 identified units for two-shift operation is estimated to cost Rs. 30,200 crore.

The committee noted, however, that NTPC has consistently declined to nominate any unit for two-shift operation pilot studies despite multiple written requests and directions from CERC. NTPC sought exemption from participating in the pilots, citing technical and operational constraints and reliability concerns. It also argued that the impacts on plant life and forced outages would emerge only after two to three years, making data generated from a trial unreliable.

Recommendations

The committee recommended avoiding consecutive ramp-up and ramp-down operations on the same units and instead distributing flexible duties fairly among all suitable units. Ramping schedules should be rotated among a pool of units rather than being allocated strictly according to merit order.

It proposed that a set of plants ramp down to MTL in the morning, operate at minimum load during solar hours and ramp up in the evening, with sufficient stabilisation time provided before the direction of ramping is reversed. The committee also recommended introducing a “ramping block” concept under which the target load is achieved at the end of the block, with generation at approximately 50% of scheduled generation. It proposed multiplying 0.5 with schedule generation during ramping to avoid DSM penalties.

Stable-load stabilisation blocks should be introduced between ramping blocks to allow units to stabilise. The committee further recommended that fine grid balancing be undertaken using hydro, gas, pumped storage and battery energy storage systems (BESS), rather than relying primarily on the thermal fleet.

The existing CERC compensation mechanism for operation at 55% MTL should be expanded to cover incremental O&M costs of up to a maximum of 5% arising from low-load operation, in addition to compensation for auxiliary power consumption (APC), specific heat rate (SHR) and oil consumption degradation.

The committee also recommended that State Load Despatch Centres (SLDCs) and Regional Load Despatch Centres (RLDCs) optimise dispatch based on available operating margins, with final optimisation undertaken by the National Load Despatch Centre (NLDC) for cross-regional renewable energy absorption. Online, real-time intelligent monitoring systems for thermal stress and Below Technical Load (BTL) prediction may also be implemented across generating units.

OEMs, meanwhile, should declare unit capabilities relating to ramp rates and parameter deviations as stipulated in contract specifications.

For the 151 identified units, the committee recommended suitable retrofitting measures following feasibility studies. It said these measures could enable an additional 12-15 years of operation and provide the grid with an equivalent 27 GW of virtual storage.

The committee also recommended an exemption from Flue Gas Desulphurisation (FGD) compliance for old Category A and B units operating in two-shift mode. It said their daily average SO₂ and other emissions would be substantially reduced because of an eight-hour daily shutdown during solar hours.

NTPC dissent

NTPC submitted a dissent note to the draft report, arguing that the analysis was based on data from only two units and could not be extrapolated to the entire thermal fleet. NTPC reiterated that a uniform 55% MTL should be specified for all thermal stations and that intra-state and regional Independent Power Producer (IPP) stations should be brought under SCUC, SCED and Ancillary Services.

NTPC also emphasised that the cost of BESS is declining sharply and that storage solutions are expected to play a critical role in balancing the grid. According to NTPC, this could reduce the need for deep flexible operation or two-shift operation of thermal power plants.

The featured photograph is for representation only.