A new substation, as part of the interstate transmission system (ISTS) network, has been proposed in Assam as an alternative path for interconnection between the northeastern region (NER) and eastern region (ER) grids.
Currently, the Bongaigaon substation is the gateway to the NER grid as all synchronous interconnections to NER originate from this substation. Now, as Bongaigaon is a flood-prone area, the North Eastern Region Load Dispatch Centre (NERLDC), way back in 2020, said that as all ER-NER AC interconnections are solely through the Bongaigaon substation, any mishap at the substation could jeopardize the supply situation to the entire NER.
The Central Transmission Utility of India Ltd (CTUIL), in response to NERLDC’s proposal, has supported the creation of a new 400kV substation at Bornagar in Assam. While the proposed substation will be at 400kV level, there will be a provision to establish 765kV and 220kV voltage levels in future.
The new Bornagar substation, which will be a 400kV ISTS switching station, is proposed to be set up with loop-in, loop-out (LILO) of the existing 400kV double-circuit (quad) Bongaigaon–Balipara line, and establishment of a new 400kV D/C (quad) Alipurduar–Bornagar line by shifting of the existing 400kV D/C (quad) Alipurduar–Bongaigaon line from Bongaigoan substation to the proposed Bornagar substation.
Hence, a major portion of this project, apart from setting up the Borngagar substation itself, will be disconnection of 400kV D/C (quad) Alipurduar-Bongaigaon line from Bongaigaon end and extension of the line for termination at Bornagar substation, so as to form the 400kV D/C (quad) Alipurduar-Bornagar line. The additional section will run around 110 km.
The existing substations at Alipurduar, Balipara and Bongaigaon, along with their connecting lines, are all owned by Power Grid Corporation of India Ltd (PGCIL).
The setting up of the new Bornagar ISTS switching substation, along with the line shifting discussed above and various other ancillary components like switchable line reactors, will be housed under an interstate transmission system (ISTS) scheme called “North Eastern Region Expansion Scheme – XXV” or “NERES-XXV,” expected to cost around Rs.833.24 crore, as estimated by National Committee on Transmission (NCT).
NCT is expected to deliberate on this scheme in its next meeting. The committee will also suggest the mode of implementation — whether TBCB or RTM. As the proposed scheme is expected to cost over Rs.500 crore, concurrence of the Union power ministry will also be needed.
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