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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