Nimesh Katariya CTU (Central Transmission Utility) is PGCIL operating India's national high-voltage transmission grid. STU (State Transmission Utility) operates each state's high-voltage transmission. Both involved in utility-scale solar grid connection.
Key Takeaways
- CTU = central transmission utility (PGCIL).
- STU = state-level transmission utility.
- Both involved in utility-scale solar interconnection.
- CTU handles inter-state ≥ 220 kV; STU intra-state.
- Distinct from DISCOMs (distribution).
CTU vs. STU: How the Split Works
The dividing line between the two is voltage class and geography, not project size alone. STUs, bodies like GETCO in Gujarat, own and operate each state’s transmission network up to the point where a line would need to cross state borders or step up to the highest voltage tiers. Once a solar plant’s interconnection voltage reaches roughly 220 kV, or its power needs to flow into another state’s grid, the CTU (PGCIL) takes over as the counter-party, and the project moves under CEA Connectivity Regulations rather than purely state-level rules.
A worked example: a 150 MW ground-mount plant in Gujarat that evacuates power entirely within the state at 132 kV would apply to GETCO as the STU and follow state-level connectivity procedures. A larger plant selling power to a buyer in a different state, or one whose evacuation line is sized at 220 kV and above, would instead route its connectivity application through the CTU and CEA’s inter-state transmission framework. Either way, the electrical safety approval from CEIG still runs as a separate, parallel process before energization, CTU/STU sign-off on the grid connection and CEIG sign-off on installation safety are not substitutes for each other.
Related Reading
Utility-scale ground-mount projects are exactly the kind of installation where the CTU/STU distinction matters, smaller rooftop and commercial systems interconnect through the local DISCOM and rarely touch either transmission utility, a contrast covered in more state-level permitting detail in our guide to solar permits across India. For teams designing the plant itself, Heaven Designs’ EPC affiliate has documented ground-mount execution in practice on its ground-mount solar park EPC page, which is useful context for how transmission-level interconnection fits into the broader project timeline.
Frequently Asked Questions
6 commonly searched questions about CTU / STU.
What's the difference between CTU and STU?
Which utility-scale solar projects fall under CTU vs. STU?
Is CTU the same as PGCIL?
Who is the STU for my state?
Are CTU and STU the same as a DISCOM?
Do rooftop or small commercial solar systems deal with CTU or STU?
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