What is the Inter State Transmission System (ISTS)

Aug. 7, 2025

About 26 gigawatt of renewable energy (RE) projects are expected to be impacted with the end of waiver on inter-State transmission system (ISTS) charges provided for solar and wind projects, according to Crisil Ratings.

About Inter State Transmission System (ISTS):

  • It is a high-voltage power transmission network that enables electricity to flow seamlessly across state borders in India.
  • It connects power-rich regions with energy-deficient areas.
  • This ensures a balanced and efficient distribution of electricity.
  • It is managed by the Central Transmission Utility of India Limited (CTUIL), a 100% subsidiary of Power Grid Corporation of India Limited (POWERGRID) under the Ministry of Power.
  • ISTS operates at voltages above 132 kV and reduces transmission losses and enhances grid stability.
  • This system allows solar and wind power to be transmitted nationwide and plays a crucial role in large-scale ISTS renewable energy projects.
  • ISTS eliminates state-wise transmission restrictions and creates a unified energy market where electricity can be supplied based on demand.
  • Overcoming geographical constraints, ISTS makes the power sector more reliable and efficient.
  • Working:
    • Power Generation: Electricity is generated from various sources, including solar farms, wind parks, hydro plants, and thermal stations.
    • Grid Connection: The generated power is transmitted to ISTS substations, which are high-voltage facilities managed by the Central Transmission Utility (CTU). These substations step up the voltage to reduce transmission losses.
    • High-Voltage Transmission: The electricity is transported through a network of 132 kV and above transmission lines that span multiple states, ensuring minimal energy loss over long distances.
    • Load Management: The Regional Load Dispatch Centers (RLDCs) and the National Load Dispatch Center (NLDC) monitor and regulate electricity flow, ensuring supply matches demand.
    • Distribution to Consumers: Power is stepped down at state-level substations and supplied to industries, businesses, and residential areas via the State Transmission Utility (STU) and local distribution networks.

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