The Tamil Nadu Electricity Regulatory Commission (TNERC) has notified the Tamil Nadu Electricity Grid Code, 2026, to address increasing renewable penetration and enhance grid stability.

The new Code will come into force from the date of its publication in the Tamil Nadu Government Gazette.

The Code applies to the State Load Despatch Centre (SLDC), State Transmission Utility (STU), transmission licensees, distribution licensees, generating companies, open access consumers, and all other users connected to or using the intra-state transmission and distribution systems.

TNERC clarified that the procedures for scheduling and dispatch of power will henceforth be governed strictly by this new Code.

The SLDC has been tasked with ensuring integrated grid operation, supervision, and compliance monitoring, and users are mandated to comply with directions issued for maintaining grid security and efficiency.

Requirements for Solar and Wind Generators

SLDC will make every effort to evacuate available solar and wind power and treat them as must-run stations. However, SLDC may instruct the solar or wind generator to reduce generation to ensure grid security or to prevent endangerment of equipment or personnel, and the solar or wind generator must comply.

The commercial operation date for units of renewable generating stations of 5 MW and above will be the date declared by the generating station after a successful trial run and submission of the declaration, subject to the fulfillment of any other conditions, if any, as per the Power Purchase Agreement (PPA).

Reactive Power and Voltage Support

Renewable generators, particularly wind and solar plants connected at Extra High Voltage (EHV) levels, will be subject to reactive power management obligations. The Code requires the operation of voltage control systems and mandates compliance with the Central Electricity Authority (CEA) technical standards.

Commercial Operation

The Code lays down detailed provisions for the drawal of start-up power and the injection of firm power during the commissioning stage of generating stations.

A generating unit that has been granted connectivity to the intra-state transmission system may interchange power with the grid during commissioning, including testing and full-load trials, only with prior permission of the SLDC and subject to grid security considerations.

The drawal of start-up power has been permitted up to 15 months prior to first synchronization and up to one year thereafter.

Injection of infirm power has been permitted for up to one year from first synchronization for non-renewable generating stations, while renewable energy generating stations and Energy Storage Systems (ESS), except pumped hydro storage project ESS, are allowed infirm power injection only up to 45 days from first energisation and integration approval.

Grid Operation

The Code emphasizes strict operational discipline for critical grid elements. SLDC, in consultation with SRLDC and users, will prepare a list of important elements essential for grid security. These elements cannot be taken out of service without prior SLDC approval, except in emergencies.

Any switching off or tripping of such elements must be immediately reported, along with reasons and estimated restoration time, and restoration must be supervised in coordination with SRLDC and the National Load Despatch Center.

Generating units are required to maintain automatic voltage regulators (AVRs), power system stabilizers, and related voltage control systems in operation in accordance with CEA Connectivity Standards. If a generating unit above 100 MW operates without an AVR or voltage controller, it must inform SLDC and obtain permission.

The Code also provides that important grid elements critical to state grid operation cannot be taken out of service without prior SLDC approval. The provision is particularly relevant in renewable-rich corridors where transmission outages could affect renewable energy evacuation.

Frequency and Voltage Management

The Code mandates coordinated action by all users to maintain system stability. The rated frequency is fixed at 50 Hz, with normal operation within 49.9–50.05 Hz. SLDC must measure frequency with high precision and archive data at 1-second intervals.

In the event of falling frequency, SLDC may issue dispatch instructions to generators or direct DISCOMs to manually reduce load or implement automatic load shedding. During a frequency rise, SLDC coordinates with generators and DISCOMs to restore frequency and, if required, lift load shedding.

Boundaries Between Systems

The Code clearly defines electrical and jurisdictional boundaries between generating stations, transmission systems, distribution systems, captive generators, HV consumers, and interstate systems.

The boundary between a generating station and the transmission system is the line isolator of the feeder injecting power into the transmission system. Similarly, boundaries between transmission and distribution systems are defined at specific isolators or transformer points.

For interstate transmission links, boundaries are determined through mutual agreement between the Central Transmission Utility (CTU) and STU, with such agreements submitted to the Regional Power Committee.

Reporting and Monitoring

According to the Grid Code, SLDC must prepare daily and monthly reports on grid performance and publish them on its website. Monthly reports must include frequency profiles, voltage profiles, major generation and transmission outages, transmission constraints, non-compliance instances, and grid security events leading to curtailment.

Quarterly reports must detail system constraints, security standard deviations, and user actions, and must be submitted to the Commission within one week of issuance.

Metering Code

The Code provides extensive provisions on metering standards, ownership, testing, inspection, calibration, sealing, and dispute resolution.

It sets minimum technical requirements for current transformers and voltage transformers, prescribes data collection systems, and establishes procedures for assessing consumption in the event of defective meters.

In 2024, TNERC unveiled the Forecasting, Scheduling, and Deviation Settlement and Related Matters for Wind and Solar Generation Regulations. The regulations were designed to support the integration of wind and solar energy into the Tamil Nadu grid, ensuring stability and security in accordance with the state grid code and relevant legislation.

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